Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts

Pathways through the Avebury Landscape – MSc dissertation

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Pathways through the Avebury Landscape

A study of spatial relationships associated with

the Beckhampton Avenue, Avebury, Wilts.

A dissertation submitted in partial fulfilment of the requirements for MSc (Archaeological Computing) by

instructional course

September 2001.


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Table of contents. INTRODUCTION; .................................................................................................................. 1

Historical background – Avebury Region. ...................................................................... 1 Theoretical Background – moving and experiencing; ..................................................... 4 Technological Background – GIS and three-dimensional reconstruction; ...................... 5

Geographic Information Systems; ............................................................................... 6 Three-dimensional Reconstructive technologies;........................................................ 6

Methodological background – analysing and visualizing;............................................... 8 AIMS AND OBJECTIVES ..................................................................................................... 12

General aims; ................................................................................................................. 12 Dynamic spatial relationships;....................................................................................... 13 Specific hypotheses; ...................................................................................................... 14

METHODOLOGY ................................................................................................................ 16 The three-dimensional reconstruction; .......................................................................... 16 The GIS;......................................................................................................................... 20 Linking the two;............................................................................................................. 22 Presentation of results;................................................................................................... 24

RESULTS ............................................................................................................................ 26 Results of the viewshed analyses;.................................................................................. 26 Results from the three-dimensional reconstruction; ...................................................... 28

DISCUSSION OF RESULTS .................................................................................................. 30 CRITIQUE OF THE METHODOLOGIES EMPLOYED ........................................................... 33

Implementing the GIS; .................................................................................................. 33 Constructing a three-dimensional reconstruction; ......................................................... 37 Using scripts to provide a dynamic link; ....................................................................... 38 Presentation of results;................................................................................................... 39

CONCLUSIONS ................................................................................................................... 40 BIBLIOGRAPHY ................................................................................................................. 43

Books, papers and journals; ........................................................................................... 43 World-wide-web references;.......................................................................................... 45

APPENDICES ...................................................................................................................... 47 Appendix I: Elevation model images............................................................................. 47 Appendix II: Cumulative viewsheds.............................................................................. 48 Appendix III: Frames from the Avenue viewshed animation........................................ 50 Appendix IV: Viewsheds calculated from locations around the study region............... 64 Appendix V: Rendered images from the three-dimensional reconstruction.................. 70 Appendix VI: Maps used in the project ......................................................................... 73


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Appendix VII: The “GoScript” Java program source code ........................................... 74 Appendix VIII: the VRML code designed to house GoScript....................................... 78 Appendix IX: the customised Avenue viewshed script ................................................. 78

ACKNOWLEDGEMENTS..................................................................................................... 79

List of illustrations

FIGURE 1: PLAN OF LONGSTONES FIELD ................................................................................... 2 FIGURE 2: STUKELEY'S 1723 SKETCH OF THE WESTERN TERMINUS OF THE BECKHAMPTON

AVENUE ............................................................................................................................ 3 FIGURE 3: TENTATIVE INTERPRETATION OF THE STONE SETTINGS AT THE COVE (GILLINGS ET

AL. 2000)........................................................................................................................... 3 FIGURE 4; THREE-DIMENSIONAL RECONSTRUCTION OF ONE OF THE WEST KENNET AVENUE

STONES, FROM THE NEGOTIATING AVEBURY PROJECT ....................................................... 7 FIGURE 5; STUKELEY'S SKETCH OF THE BECKHAMPTON AVENUE, 1723 ................................ 15 FIGURE 6; SIMPLIFIED REPRESENTATION OF A RASTER DEM SHOWING POSITIVE AND

NEGATIVE LOS VECTORS................................................................................................ 34 FIGURE 7; THE EFFECTS OF DEM RESOLUTION ON LOS VECTORS.......................................... 35 FIGURE 8: THE SAME SCENE VIEWED IN DIFFERENT BROWSERS TO SHOW INCONSISTENCIES

(GOODRICK, 1997) .......................................................................................................... 38 FIGURE 9: ELEVATION MAP OF THE 'FINAL STUDY REGION'.................................................... 47 FIGURE 10: CUMULATIVE VIEWSHED OF POINTS ALONG THE BECKHAMPTON AVENUE......... 48 FIGURE 11: CUMULATIVE VIEWSHED, AS FIG.2, POST APPLICATION OF SMOOTHING ............. 49 FIGURE 12: AVENUE VIEWSHED ANIMATION - FRAME 1 ......................................................... 50 FIGURE 13: AVENUE VIEWSHED ANIMATION - FRAME 2 ......................................................... 50 FIGURE 14: AVENUE VIEWSHED ANIMATION - FRAME 3 ......................................................... 51 FIGURE 15: AVENUE VIEWSHED ANIMATION - FRAME 4 ........................................................ 51 FIGURE 16: AVENUE VIEWSHED ANIMATION - FRAME 5 ......................................................... 52 FIGURE 17: AVENUE VIEWSHED ANIMATION - FRAME 6 ......................................................... 52 FIGURE 18: AVENUE VIEWSHED ANIMATION - FRAME 7 ......................................................... 53 FIGURE 19: AVENUE VIEWSHED ANIMATION - FRAME 8 ......................................................... 53 FIGURE 20: AVENUE VIEWSHED ANIMATION - FRAME 9 ......................................................... 54 FIGURE 21: AVENUE VIEWSHED ANIMATION - FRAME 10 ....................................................... 54 FIGURE 22: AVENUE VIEWSHED ANIMATION - FRAME 11 ....................................................... 55 FIGURE 23: AVENUE VIEWSHED ANIMATION - FRAME 12 ....................................................... 55 FIGURE 24: AVENUE VIEWSHED ANIMATION - FRAME 13 ....................................................... 56 FIGURE 25: AVENUE VIEWSHED ANIMATION - FRAME 14 ....................................................... 56 FIGURE 26: AVENUE VIEWSHED ANIMATION - FRAME 15 ....................................................... 57 FIGURE 27: AVENUE VIEWSHED ANIMATION - FRAME 16 ....................................................... 57


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FIGURE 28: AVENUE VIEWSHED ANIMATION - FRAME 17 ....................................................... 58 FIGURE 29: AVENUE VIEWSHED ANIMATION - FRAME 18 ....................................................... 58 FIGURE 30: AVENUE VIEWSHED ANIMATION - FRAME 19 ....................................................... 59 FIGURE 31: AVENUE VIEWSHED ANIMATION - FRAME 20 ....................................................... 59 FIGURE 32: AVENUE VIEWSHED ANIMATION - FRAME 21 ....................................................... 60 FIGURE 33: AVENUE VIEWSHED ANIMATION - FRAME 22 ....................................................... 60 FIGURE 34: AVENUE VIEWSHED ANIMATION - FRAME 23 ...................................................... 61 FIGURE 35: AVENUE VIEWSHED ANIMATION - FRAME 24 ....................................................... 61 FIGURE 36: AVENUE VIEWSHED ANIMATION - FRAME 25 ....................................................... 62 FIGURE 37: AVENUE VIEWSHED ANIMATION - FRAME 26 ....................................................... 62 FIGURE 38: AVENUE VIEWSHED ANIMATION - FRAME 27 ....................................................... 63 FIGURE 39: AVENUE VIEWSHED ANIMATION - FRAME 28 ....................................................... 63 FIGURE 40: VIEWSHED CALCULATED FROM THE HYPOTHESISED WESTERN END OF THE

AVENUE .......................................................................................................................... 64 FIGURE 41: VIEWSHED CALCULATED FROM THE WESTERN HENGE ENTRANCE, THE EASTERN

END OF THE AVENUE....................................................................................................... 65 FIGURE 42: VIEWSHED CALCULATED FROM THE COVE, LONGSTONES FIELD ........................ 66 FIGURE 43: VIEWSHED CALCULATED FROM LONGSTONES LONGBARROW............................. 67 FIGURE 44: VIEWSHED CALCULATED FROM SILBURY HILL.................................................... 68 FIGURE 45: VIEWSHED CALCULATED FROM THE SOUTHERN BANK OF WINDMILL HILL ........ 69 FIGURE 46: THE ENCLOSURE IN LONSGTONES FIELD.............................................................. 70 FIGURE 47: THE AVENUE AND COVE, LONGSTONES FIELD .................................................... 70 FIGURE 48: THE SECOND PHASE OF THE COVE, LONGSTONES FIELD...................................... 71 FIGURE 49: THE HYPOTHESISED EXTENSION TO THE AVENUE BEYOND THE COVE,

LONGSTONES FIELD ........................................................................................................ 71 FIGURE 50: VIEW FROM ATOP SILBURY HILL LOOKING TOWARDS LONGSTONES LONG-

BARROW .......................................................................................................................... 72 FIGURE 51: VIEW FROM WINDMILL HILL TOWARDS LONGSTONES FIELD.............................. 72 FIGURE 52: HISTORIC OS MAPS OF THE AREA ......................................................................... 73 FIGURE 53: MODERN OS MAPS OF THE REGION ...................................................................... 73


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Introduction;

This project is an investigation into the spatial relationships associated with the

Beckhampton Avenue, Avebury, Wilts. through the Neolithic period; The study

region comprises the Beckhampton avenue and its environs. Notably, the study will

attempt to investigate dynamic spatial relationships, i.e. those associated with moving

around/through a landscape rather than from static viewpoints, as a means to shed

light on the position and development of the Beckhampton Avenue, which can be

seen as a formalised route, influencing movement. These relationships are to be

investigated by means of the concept of intervisibility using both the analytical

approach afforded by GIS techniques and a more subjective, reflexive approach

facilitated by an interactive three-dimensional model †.

Historical background – Avebury Region.

The Avebury complex comprises a substantial number of archaeological

monuments dating from the Early Neolithic through to the Early Bronze Age. The

earlier monuments comprised mainly long-barrows, including South Street and the

chambered tombs at West Kennet and East Kennet; there were also ditched enclosures

on Windmill Hill and in Longstones Field and the first phase of a henge at Avebury

itself as well as the first phase of activity at the Sanctuary on Overton Hill (see

Appendix I: Fig.9.). As the Neolithic progressed, the number of monuments increased

as the complex grew; apparent routes between monuments were formalised with stone

avenues, at West Kennet and Beckhampton, and older monuments were demolished,

replaced, added to or otherwise changed, as happened in Longstones Field and at the

henge itself. By the end of the Neolithic, a network of spatial relationships had been

defined by the monuments that had been placed within the landscape so that both

movement and vision were influenced.

† The term ‘three-dimensional reconstruction’ will be used in preference to any derivative of the

term ‘virtual-reality’ due to the problematic nature of the latter term (Gillings. 1997), especially in an

analytical context such as this project.


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Figure 1: Plan of Longstones Field

In Longstones field, a series of developments took place during the Neolithic. In

sight of both South Street and Longstones long barrows, the first phase of

development consisted of an oval, ditched enclosure with an entrance at one end,

roughly contemporary with the initial development at the henge itself. This enclosure

was relatively short-lived, with no evidence for re-cutting and only a thin turf line

having formed before the ditch was backfilled (Gillings, et. al. 2000. p13). This act of

backfilling may well have left a noticeable rise along the path of the ditches for some

time after the event (Wheatley, pers. comm.). Once the enclosure had been removed

from the landscape, at least in its original form, the initial phase of construction

involving megaliths began with a stone setting being erected at the Cove and the

Avenue; this initial setting was subsequently remodelled to form a rectilinear stone

setting, as shown in Fig.3. It is hypothesised that the avenue may have either ended at

the Cove or continued west towards the Beckhampton Road long barrow; Stukeley

hypothesised that the western terminus of the Avenue was near to the barrows at Fox

Culvert.


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Figure 2: Stukeley's 1723 sketch of the western terminus of the Beckhampton Avenue

The Beckhampton Avenue may well have continued beyond the Cove, as Stukeley

came to think, despite the lack of any recent evidence from excavation or field survey:

As well as Stukeley’s testimony, a sarsen burial pit was found on the projected line of

the Avenue by the modern day Calne Road (Gillings et al. 2000. 14).

Figure 3: tentative interpretation of the stone settings at the Cove (Gillings et al. 2000).


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Theoretical Background – moving and experiencing;

Movement is something humans do all the time and while we do we experience.

As Thomas argues: “The identification of locations as the ‘place of’ something

demonstrates the relational character of place. Human lives thread their way through

spaces and in the process our memories of having been are localised” (Thomas, 1996.

89). As such, movement plays a key role in forming society. It has recently been

argued that double-entrance henges are in some way associated with movement; i.e.

passage through the monument (Loveday, 1998. 17). Although Avebury is not a

double-entrance henge, the multiple entrances and the two avenues would suggest that

the concept of movement was involved in the design of the henge. If we assume,

therefore, that the avenues are associated with the movement of people through the

Avebury complex, we can start to investigate how this movement provides a

particular perception of the region. Loveday also noticed an association between the

alignments of double-entrance henges and much later route-ways where there can

have been no significant archaeological relationship between them; the inference

being that both the henge alignments and the later road alignments are related to

notions of thoroughfare (ibid.). Loveday also notes that the modern concept of a path

is not necessarily applicable to ancient route-ways (ibid. p24-5); rather than being

clearly defined, ancient routes were braided and very much interpretative, whereby

users were free to pick their way along a general path, guided by their surroundings.

Indeed, Ingold suggests that to primarily mobile populations (and there is scant

evidence for large-scale settlements from the study period in Wessex) the notion of

paths and places is more applicable than borders and territories (Ingold, 1980). In the

Early Neolithic Avebury region, the patterns of intervisibility associated with long

barrows suggests that each barrow was placed in a discreet visibility envelope

(Wheatley, 1996); as such, each barrow was revealed in turn as one passed through

the landscape. This suggests that the barrows were placed deliberately to be viewed

not from any one significant point, but as a sequence, revealed to the observer as

he/she moves through the area.

Barnatt (1998) argues that “Where people moved around the land, pathways

between places would be emphasised, and monuments sited beside them. Given the

scale of many Neolithic monuments, they may also have been placed at locales where

groups were in closer proximity at certain times of the year. At such times and places


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there was an increased propensity for both social tension and cooperation; monuments

may have been designed to both resolve and take advantage of these non-everyday

situations” (ibid. 93). In this way, the Avenues, can be seen to be the formalisation of

significant routes, routes which may have pre-dated the majority of the complex; the

other monuments can be seen to have located with respect to these routes, as Barnatt

advocates. Further to this, Thomas (1999. 202) argues that Windmill Hill causewayed

enclosure was a place used to control the transfer of people and things in and out of

the Wessex area from the Thames Valley to the north and further afield, suggesting

that the movement through the region may well have not been restricted to a small,

local population but perhaps to a much wider group of users.

Existing theory therefore suggests that through the Neolithic, we are dealing with

an experiential Avebury landscape, one in which there are special places and ways of

moving between and around them which are themselves being constantly

renegotiated; it is these ideas which are evident in the megalithic structures, other

monuments and relationships between monuments and/or their surroundings.

“Monuments played a fundamental role in the organisation of the prehistoric

landscape, helping to mark and characterise important places in the perceived scheme

of things. They were key elements in ‘sacred geographies’: Landscapes charged with

meaning” (Ruggles, 1998. 208).

Technological Background – GIS and three-dimensional

reconstruction;

Archaeologists often make use of scientific methods in order to test archaeological

hypotheses. Various forms of statistics are often employed and there is generally a

spatial attribute to archaeological data. For many years, this spatial element was

reduced to a representational tool, whereby aspects of the data could be visualized

arranged using the spatial attribute of the data. This resulted in methodologies

primarily based around the subjective interpretation of maps produced to demonstrate

particular aspects of a given dataset. On one level, applications of GIS and VR can be

seen to be a new way of representing spatial data in two and three dimensions

respectively; a continuation of the traditional way of dealing with spatial data. On

another level, three-dimensional reconstructions and GIS can be used as analytic tools

in order to devise and test hypotheses rather than simply basing hypotheses on a


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cursory visual inspection of the data: The ability to perform computationally

expensive tasks within an acceptable time span has made complex interrogation of the

spatial dataset, and calculation using the results possible.

Geographic Information Systems;

Geographic Information Systems are not a technology invented specifically for/by

archaeologists, rather they are another example of a set of tools borrowed from

another discipline. As well as being an excellent means of managing and presenting

spatial data, they include a range of analytical functions which can be informative to

archaeological investigations. It is now widely accepted that for representational or

data management purposes, in the field of cultural resource management for example,

GIS is extremely useful, but more analytic approaches, such as viewshed analyses

have received criticism for lacking any underpinning archaeological theory (e.g.

Aldenderfer, 1996). More recently, there has been a trend towards critical analyses of

the methodologies associated with using such procedures, and reflexive thought

regarding the input and output of the GIS (e.g. Fisher, 1991&1996; Gillings &

Goodrick, 1996).

This process has resulted in novel solutions to some of the criticisms levelled at the

analytic use of GIS. Of particular relevance to this project is the development of so-

called probabilistic or ‘fuzzy’ viewsheds (Fisher, 1992; Nackaerts et al. 1997),

whereby the resultant GIS output represents the probability of a particular cell falling

within the viewshed rather than a simple binary option. Issues such as this will be

dealt with in the critical evaluation section of this project.

Having said this, there are many examples of the use of GIS to inform

archaeological thought, and the continual process of developing and refining the tools

available within the GIS advances apace.

Three-dimensional Reconstructive technologies;

Again, three-dimensional modelling and visualization was not invented specifically

for/by archaeologists. The origins of three-dimensional modelling and visualization

techniques come from a range of sources including the disciplines of graphic design,

film-making, and architecture. Often used to reconstruct sites and monuments for

presentation to the public, as ubiquitously seen on Channel4’s ‘Time-Team’


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programme, three-dimensional reconstructions are often presented as an accurate

depiction of times past, with little discussion of how the reconstruction relates to the

evidence, the project aims or more abstract factors such as the budget or available

computational power. Such investigations often produce visually attractive results, but

whose archaeological integrity is perhaps questionable.

Three-dimensional reconstruction has also been used as an analytical tool to

investigate specific hypotheses. Recent work in this field has included Jennifer

Garofalini’s work on the Sanctuary, Overton Hill, Wilts., which allowed a number of

different hypotheses regarding the phases and development of the site to be

investigated. Another good example of this is the work by Wheatley, Gillings and

Goodrick on the Negotiating Avebury project, which includes a three-dimensional

reconstruction of the Henge and West Kennet Avenue. The model allows different

hypotheses regarding the position of the stones, the configuration of the entrance and

the alignment of the last section of the avenue to be investigated.

Figure 4; Three-dimensional reconstruction of one of the West Kennet Avenue stones, from the Negotiating Avebury project


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Methodological background – analysing and visualizing;

This project aims to use a combination of GIS and three-dimensional

reconstruction to elucidate the development of the Beckhampton Avenue. As such,

this project can be seen to be more closely related to analytical and theoretical uses of

such technologies rather than more representational based studies: Therefore, this

related studies section will focus on those studies which have had a direct bearing on

this investigation by using a combination of GIS or three-dimensional reconstructions

in an analytical way, particularly in conjunction with other supporting technologies,

rather than try to summarise the extensive corpus of work which makes use of GIS or

three-dimensional reconstructive techniques in general. Of particular note are the

range of studies which have attempted to use such technologies to investigate three-

dimensional spatial relationships in terms of visibility. Studies regarding the

phenomenological approach to the understanding of the development of

archaeological monuments are also relevant, as human perception and the subjectivity

of an observer must be taken into account.

The concept of visibility and intervisibility has been demonstrated to be a useful

concept for archaeologists ever since the first antiquarians travelled the country

drawing the vistas they saw. In recent years, the growth of computing has allowed

visibility studies to be performed using a range of computerised techniques, usually

adopted for the purpose. Studies which make use of the analytical qualities of GIS

systems include different types of visibility study: The ease with which computers can

calculate vast numbers of line-of-sight vectors greatly facilitates the formulation of

more advanced methodologies.

A good example of a viewshed based investigation which produced interesting

results was Wheatley’s (1996) investigation of the Early Neolithic Long Barrows of

the Avebury region. This investigation used viewsheds calculated from each barrow

in turn to show how each barrow was placed in its own distinct visibility envelope,

exposed in turn as the observer moved around the landscape.

A similar study of the Tall al-Umayri region, Jordan (Christopherson & Guertin,

1996), also used binary viewsheds calculated from points in the region to investigate

the intervisibility of the watchtowers present in the landscape. The investigation used

the observer height attribute of the viewshed calculation to represent the height of the


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walls and watchtowers, where the observer would most likely have been observing

from. This study demonstrated that although the visible area from the settlements

locations themselves were incredibly small, when each settlements network of

watchtowers was taken into account, each settlement showed a good level of control

over its respective territory, in terms of the area within the viewshed.

The calculation of viewsheds followed by their interpretation in terms of areas

visible is one of the most intuitive ways of using the GIS, but is by no means the only

way. The Tall al-Umayri investigation went further: The results from the preliminary

investigation were used to produce cumulative viewsheds over a long temporal range

for the study region. These viewsheds were used to test whether the number of

intervisible sites was statistically significant for each temporal zone compared to a

randomly generated set of sites and viewsheds.

While GIS based viewshed data can be interpreted both by visual inspection or

rigorous statistical association tests, it is often useful to further test the relationships

further; in the GIS this is not straightforward as the spatial dataset does not record

three-dimensional relationships, rather the system uses two-dimensions for recording

location with the elevation data being stored as another spatial attribute in the same

way as soil type or vegetation cover. Three-dimensional GIS is currently entering the

marketplace and is still firmly in development. This has resulted in the use of

supporting technologies which are capable of supporting corollary datasets or using

the same dataset in alternative ways, allowing the archaeologist to further test

potential relationships by whatever means.

An example of this is Gimblett et al.’s (1996) work on agent simulation, which has

attempted to use intelligent agents in three-dimensional simulated worlds derived

from GIS data to go further than would be possible using the GIS alone. The use of

intelligent agents dynamically interpreting GIS data, in order that the agents can make

decisions based on that data, has the potential to inform the archaeologist more than

evaluation of the GIS data alone.

Another good example of this is Bell’s (1998) study of the Whitby area where the

possibility of a Roman watchtower on a long eroded and disappeared section of coast

was confirmed using a combination of viewshed analyses and a CAD model of the

region. In this study, the model was used to approximate possible heights for the


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watchtower which could then be used as the observer height for further GIS viewshed

analysis. In Bell’s study, the model is not designed to reconstruct what was actually

there, but to augment the study by means of providing initial hypotheses to be tested

using the GIS: It is along these lines that this investigation of the Beckhampton

Avenue will progress, whereby the reconstruction will be used to test hypotheses

based on the results of the GIS analyses and vice-versa in a reflexive manner.

Methodologically speaking, this project can be seen to be strongly related to Earl’s

(1996) investigation of Danebury hill-fort. Earl’s methodology involved the creation

of landscape surfaces using the GRASS GIS and various modelling stages in

AutoCAD and 3D StudioMax. Unlike most reconstructions, where the modelled

structure is placed on an empty, flat plane, this methodology allows the effect of

topography to be taken into account, a factor which may prove highly significant in

the investigation of what is thought to be a formalised route-way, perhaps with far

more ancient origins.

If we now turn to some of the work relating to the perception of monuments,

particularly with respect to their visual appearance, there have a been a number of

important observations. One of the more important hypotheses with respect to this

project regards the use of colour, as described by Lynch (1998): This is critical to an

understanding of the patterns of visibility associated with the monuments that make

up the Avebury complex. The underlying bedrock is chalk, sometimes only a matter

of inches below the land-surface, and when cut into to form ditches, this white chalk

would have glowed in the light. The banks too, made up of the chalk rubble removed

from the ditches would have appeared brilliant. Factors such as these, that would

make some monuments more discernible at times of re-cutting or under different

lighting conditions, and certainly make them stand out from their surroundings,

cannot adequately be investigated using the GIS alone, but such factors can be

incorporated into the three-dimensional reconstruction for analysis. Indeed, Wood’s

(1998) paper which attempted to qualify some of the links between the analytical GIS

and the more subjective three-dimensional representation, considering factors such as

the mystery, drama, and satisfaction indices, measures of feeling or observer

experience.

Thomas’ (1999. 213-6) experiential account of moving along the West Kennet

Avenue and around the complex has also been useful in formulating ideas regarding


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how the complex may have developed. The Avebury Thomas describes is indeed an

experiential complex with many layers of meaning, some of which are associated with

the visibility relationships formed and broken as an observer moves around, and it is

against this background that this investigation of the Beckhampton Avenue will

proceed.


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Aims and objectives

The aim of this project, as already stated, is to investigate the spatial relationships

associated with the Beckhampton Avenue. Specifically, the aim is to investigate this

by means of a study of the patterns of intervisibility associated with the avenue and

associated monuments as one moves around the study region.

General aims;

The concept of movement is central to the aim of this investigation. It is possible

that the archaeologically significant relationships between monuments are not

necessarily direct, but involve a third party; the observer. In other words, while some

spatial relationships are fixed in the landscape, others are dynamically generated as

the observer moves around the landscape observing. Particular ways of moving

through the landscape will reveal a particular sequence of relationships: Some

monuments are nearly always visible, some only from within particular visibility

envelopes, and others seldom revealed. The aim is identify and investigate such

relationships in order to shed light on the development of the Beckhampton Avenue.

In order to do this, a combination of GIS and three-dimensional reconstruction was

chosen as being an ideal combination of investigative tools; the GIS can be used to

produce viewsheds for any given point in the study region while the three-

dimensional model can be used to investigate potential relationships highlighted by

the GIS. A dynamic link between the model and the GIS will provide a means of

producing three-dimensional views from within the GIS or calculating viewsheds

from within the reconstruction. It is anticipated that this link will facilitate the

reflexive nature of this investigation, whereby new ideas can be incorporated into the

system for analysis and the output from such analyses can be re-input and further

analysed.

As such, a secondary aim of the investigation is to critically evaluate the usefulness

of the chosen methodology in terms of the archaeological significance of the results

and the effectiveness of the system used. While it is believed that there is a sound

theoretical framework underpinning this investigation, the actual implementation will

be constrained by factors beyond control: The quality of the source data used,


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computer software/hardware limitations as well as time restrictions will all have a

bearing on the final project results. Indeed, the decisions made throughout the project

will also have been contributory to the results obtained. As such, it will be a

worthwhile exercise evaluating the ways in which such issues have impacted on the

project as a whole: As Hodder suggests, it is only through reflexivity and self-

criticism that research gains credibility in lieu of claims of objectivity (Hodder, 1999.

208).

The project aims are summarised below:

1. To investigate dynamic spatial relationships associated with moving

through the study region.

2. To construct a three-dimensional reconstruction and a GIS for the study

region, to facilitate 1.

3. To evaluate the effectiveness of the chosen methodology.

Dynamic spatial relationships;

One of the key aspects to this project is the idea of dynamic spatial relationships,

i.e. those which are constantly created and destroyed as an observer moves around a

landscape. There has already been much work using the notion of visibility defining

some of the static relationships between monuments in the Avebury complex (e.g.

Devereux, 1991 and Wheatley, 1996) which has demonstrated that some monuments

can be seen from others and that some monuments are placed in distinct visibility

envelopes. An aim of this project is to investigate the sequences in which

relationships between an observer and the monuments are formed, in terms of lines-

of-sight: This will be achieved by means of a dynamic link between a GIS and a

VRML model to allow movement through a virtual Avebury, where observations can

be made directly, while at the same time interrogating the spatial database, where

representations of the visibility envelopes, or viewsheds, can be output.

This dynamic link will be facilitated using the scripting facilities built into the

ArcView GIS, from ESRI. The aim is to provide an interface between the GIS and the

VRML world, which will involve passing data from the GIS to the VRML-enabled

web-browser, with the objective that potential sequences of relationships between the

observer and elements of the complex can be identified using the GIS and further


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investigated using the model before, if necessary, performing further analysis using

the GIS.

Specific hypotheses;

From an initial inspection of the model, a number of ideas emerged. In a similar

way to the arrangement of long barrows in the area, it would appear that the avenue is

positioned in such a way as to control what is visible to an observer travelling along

the avenue. Indeed, Thomas (1999. 214-6) has commented on the experiential nature

of the West Kennet Avenue and how the path the Avenue takes serves to control what

enters an observers visibility envelope and when. If the West Kennet Avenue is seen

as analogous to the Beckhampton Avenue, then it would seem logical to assume a

similarly controlled experience. As such, this investigation will focus on how the

viewshed changes along the Beckhampton Avenue in order to test the hypothesis that

this Avenue was carefully placed in relation to the surrounding topography and

existing monuments.

The Avenue may or may not have continued past the Cove in Longstones Field;

Stukeley certainly recorded it as far as the barrows at Fox Culvert, where he claimed

it terminated. If this was indeed the case, then it would be interesting to investigate

the associated patterns of visibility to test the hypothesis that this stretch of the

Avenue too was carefully placed with respect to the visibility of the other monuments

in the complex.


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Figure 5; Stukeley's sketch of the Beckhampton Avenue, 1723

The Cove in Longstones Field and the Beckhampton Avenue are assumed to be a

parts of a multi-phase monument (Gillings et al. 2000. 14-5), with the Cove marking

an original terminal to the Avenue. This would mean that Stukeley’s recorded stretch

is an addition: The three-dimensional reconstruction can be used to investigate

different phase arrangements in order to test this hypothesis.


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Methodology

As there are a number of distinct elements to this aspect of the project, each one

will be dealt with in turn.

The three-dimensional reconstruction;

The process of creating a three-dimensional reconstruction consisted of two

distinct modelling stages: The monuments themselves and the landscape on which

they are positioned. The process of modelling the various elements involved the use

of a number of different tools available in various software packages. AutoCAD R14

was used for the initial accurate modelling stages and georeferencing while later

assembly stages made use of the intuitive interface of 3D StudioMax. A number of

other utilities were used for various specific tasks along the way.

The barrows were modelled using AutoCAD, based on existing digitised base

plans, known measurements and accounts of the size and shape of the barrows. The

barrows were modelled using solid modelling techniques in order to facilitate later

stages of the methodology. The base plans, being georeferenced, enabled the model

elements to be constructed using real-world coordinates. The enclosures, on Windmill

Hill and in Longstones Field, were modelled using a similar range of techniques. The

measurements were once again based on existing excavation data.

The avenue and cove both involved a different set of techniques. The megaliths

were all based on generic rock-type surface models, freely available on the internet:

These models came in the form of three-dimensional triangulated wire-frames. These

rocks were deformed using the modifiers available in 3D StudioMax, which allow

fairly freeform, intuitive three-dimensional deformation, facilitating creating stones of

approximately the right shape and size. Having been satisfactorily modelled, the rocks

were exported as dxf files to be imported into AutoCAD where the individual rocks

could be placed in their appropriate georeferenced locations. A number of different

rocks had to created, as detailed in the table.


17

Once the individual monuments had been modelled, each element was imported

into 3D StudioMax for the final assembly of the monumental complex. As each

element had been modelled using real-world coordinates, the x and y spatial attributes

of the complex as modelled was correct, although at this stage, the z (elevation)

attribute was limited to being correct within the individual elements only. The next

stage, construction of the landscape surfaces, would alleviate this problem by

providing elevation data for the model.

Creating three-dimensional landscapes has been crucial in the disciplines of

computer generated art and computer gaming although the focus of development has

been the generation of aesthetically pleasing landscapes rather than being an accurate

representation of a given spatial dataset. As such, many of the tools available for

creating landscapes in commercially available software packages are not suitable for

creating accurate representations of DEMs: There are becoming increasingly available

dedicated landscape modelling packages capable of importing a variety of commonly

available GIS software formats although these are currently very expensive,

commercially available packages, not suited to such a project as this. The

methodology adopted is reflective of the software available and the need for a

justifiable level of accuracy over purely aesthetic values.

The landscape surfaces needed to be of an acceptable level of accuracy in order

that the model is representative of the real-world situation, essential if the model is to

be used to test hypotheses based on the concept of visibility. There are, however,

problems with this approach. Firstly, a high level of detail (LOD) requires a high

number of surface nodes. Secondly, there are constraints on the number of surface

nodes which can be used within a given surface, both those defined as part of the

VRML standard and also those imposed by available computational power. These two

considerations must be considered together with the resultant surface being an

acceptable compromise between the two. A good way of representing surfaces with

an acceptable LOD whilst reducing the number of nodes is as a Triangular Irregular

Male Avenue stone Tall, thinner stones – approx 2-2.5m high Female Avenue stone Squatter, squarer stones – similar height Beacock stone Massive stones, analogous to obelisk at the henge (?) – approx

3-4m high Adam (cove stone) Massive, rectangular slabs – based on the still standing Adam

stone Eve (final avenue stone) Slightly larger avenue stone adjacent to cove – based on the still

standing Eve stone


18

Network (TIN) rather than an Elevation Grid: Unlike the Elevation Grid, the TIN does

not have a fixed sample rate allow more nodes to be used to represent areas of the

surface with the greatest amount of change. The process of creating and

georeferencing such land-surfaces involves a number of different steps, outlined

below:

The original dataset consisted of digitised 1:50,000 contour data for a 20km square

around Avebury. It would be impossible to use the whole of this dataset for the

construction of a model due to the sheer scale; instead, it was decided to create a

surface based on a smaller region, a subset of the data, but on which all of the

monuments being modelled could be placed. Initially, it was intended to interpolate

the contour data at a five meter resolution although it soon became apparent that the

area which could be modelled at this resolution would be too small and there would

be questions relating to the validity of such an interpolation, given the resolution of

the original dataset. Given the need for a large enough study region, and the resolution

of the original data, it was decided to interpolate a larger DEM at a resolution of ten

meters. The regions defined in the GRASS GIS are detailed in the following table:

Region Name Lower-Left corner Upper-Right corner Interpolated DEM resolution

No. cells

FinalStudyRegion 407000,168000 411000,172000 10m 400x400

MiddleBit 408475,168775 410625,170425 5m 430x330

Having defined suitable regions, DEMs of each were produced. This was

accomplished by sampling the vector data at the required resolution using the v.to.rast

command; the resultant file was then used as the input for the r.surf.contour

command, which uses an algorithm to interpolate elevation values for each pixel in

the resultant raster output file. The resultant DEMs were then output as ASCII text

files using the r.out.ascii command ready for the next step of the methodology.

Step1: Export DEM from GRASS as ASCII raster Step2: Produce VRML Elevation Grid from DEM using LandSerf Step3: Clean/validate VRML using Chisel

Split Elevation Grid into compound Elevation Grid using Chisel Step4: Import VRML into 3d StudioMax

Apply ‘simplify grid’ modifier to each of the grid objects Step5: Export all of the grid objects as a dxf file, with all objects on one layer

Step6: Import into AutoCAD Scale and position grids to real-world coordinates Adjust base elevation of grids to real-world elevation


19

The next step was to create surfaces based on the DEMs output from GRASS. This

was achieved using the LandSerf GIS package which has the ability to import GRASS

ASCII raster files and export VRML elevation grids. There is native support within

GRASS for producing VRML format output using the v.out.vrml command but,

unfortunately, this was not available at the time of this project. The resultant elevation

grids, in their original state, contained vast amounts of redundant elevation data;

indeed, given that LandSerf exports one elevation grid square for each cell in the

original DEM, the number of nodes far exceeded the maximum permissible number

of 16000. This led to the need to further process the elevation grid files in order to

make them useable. For this, a package called Chisel was used which includes a suite

of tools for optimising, cleaning and validating VRML files. Each Elevation Grid was

split into a number of smaller spatially referenced grids, which when displayed

together appear indistinguishable from the original grid, but each one with fewer than

the maximum permissible number of nodes: This operation resulted in a considerable

reduction in file size and removed all VRML non-complicity errors.

The final stage of producing the surfaces was to simplify the Elevation Grids in order

to reduce the amount of redundant data. This was achieved using the simplify grid

modifier in 3d StudioMax applied to each of the sub-grid objects, which uses a

triangulation algorithm to optimise the surfaces and reduce the number of nodes and

faces contained within a surface. This process is often referred to as ‘decimation.’

Once complete, the files were saved as dxf files for import into AutoCAD where the

surfaces were positioned and scaled to real-world coordinates.

Once the land-surfaces and monuments were complete, the AutoCAD files were

imported directly into 3D StudioMax for the final assembly stages. As the AutoCAD

files made use of real-world coordinates, at least in the x-y plane, each element was

automatically placed in the appropriate position upon import. The elevation of the

megaliths in relation to the land-surface was corrected by moving each element

manually parallel to the z-axis until it looked to be in the appropriate place in the

perspective view. The other monuments (the enclosures, henge and Silbury Hill) were

attached to the land-surface by means of a conform Space Warp. This was applied to

the base vertices of each monument and works by forcing these vertices to obtain their

z-coordinate from a user specified plane, in this case the land-surface.


20

Having corrected the relative elevations within the model, it was necessary to correct

the absolute elevation of the model as a whole in order that the three-dimensional

coordinates of any point within the model is representative of the real-world situation.

This was accomplished by moving the entire model parallel to the z-axis to the

appropriate position, based on known coordinates/elevations provided by the GIS.

Finally, textures and lighting were applied to the model before final rendering of still

images and animations. Colour bitmaps were used to provide textures for the stones

and the grass, while the same bitmaps were used as bump-maps to provide the illusion

of three-dimensional surface texture. The lighting was accomplished by means of a

sunlight system, allowing fairly realistic light to be added. The still images and

animations were rendered using a variety of resolutions and levels of detail: Generally

a small version of each animation was created, for potential web-based dissemination.

The model was then exported as a VRML world to be linked to the GIS. Additional

scripts were added manually to provide a means of controlling the phases of the Cove

and enclosure in Longstones Field.

The GIS;

The GIS part of this project involved the use of the GRASS GIS to produce the

DEMs used in the subsequent analysis, performed using ArcView. The decision was

made to implement the analytical part of the project using the ArcView GIS rather

than the GRASS GIS due to the internal structure and workings of the system:

ArcView runs on the Windows platform and is based around the Avenue scripting

language, an object-oriented language similar to Java, compared to GRASS, which

runs primarily on Unix platforms and is based around the C procedural programming

language. The use of the Windows based, object-oriented system greatly facilitated

the aim of providing a dynamic link between the GIS and the VR model.

The ArcView GIS was set up using the same data as was used for the VR model:

The interpolated DEMs output from the GRASS GIS. The ASCII raster files output

from GRASS are of a slightly different format to those accepted by ArcView. As

such, it was necessary to first modify the file-headers using a text editor to make the

files compliant with the ArcView ASCII raster file format. The differences in the file

headers is illustrated in the table below:


21

GRASS ASCII raster header ArcView ASCII raster header north: value south: value east: value west: value rows: value cols: value

Most northerly coordinate Most southerly coordinate Most easterly coordinate Most westerly coordinate Number of rows Number of columns

nrows: value ncols: value xllcorner: value yllcorner: value cellsize: value

Number of rows Number of columns x-coordinate, lower-left corner y-coordinate, lower-left corner grid resolution

Once made compliant, the ASCII raster files were imported into ArcView. Both of

the interpolated DEMs based on the original GRASS regions were imported as well as

an interpolated DEM representative of the whole area covered by the original dataset.

Features were added to the GIS by means of the CAD-reader extension, facilitating

the inclusion of AutoCAD files generated from the original two-dimensional files.

Two such files were included, one containing the prehistoric features in the region,

bounded by the World Heritage Site boundary, the other containing modern features

to facilitate understanding and interpreting the area. A third AutoCAD file was also

included which contained a line representing a theorised path along which the

Beckhampton Avenue may have continued past Longstones Field.

Binary viewsheds were calculated using a customized version of the SA: Visibility

script which is part of the ArcView vistools extension (vistools.avx) written by Esri

and available on their website. This script calculates a binary viewshed based on user

defined observer and target locations, observer and target offsets and a field of view.

For the purposes of this investigation, the offsets were both set to two metres and the

field of view was set to three-hundred-and-sixty degrees to provide a complete

viewshed.

In addition to this, cumulative viewsheds were prepared for the points along the

theorised path of the Beckhampton Avenue. This was accomplished using the

Spatial.SimpleVisibility script, the input being a digitised line in a shapefile theme

following the theorised path. The cellObserved flag was set to false in order that the

resultant product represented the frequency of each cell being observed from the

observer locations. The resultant map had a frequency range of 0-25, representing the

twenty-five observer locations (nodes) along the line.

Viewsheds calculated from points along the Avenue were then labelled and

assembled into a short animation using Macromedia Fireworks in order to illustrate

how the viewshed changes as the observer moves along the Avenue.


22

Linking the two;

The process of linking the two components of the system together involved a

number of stages. The first stage involved creating a viewshed using the GIS, the

second stage involved converting and passing data describing the view to the VRML

browser, and the final stage involved rendering the view in the browser.

Calculating viewsheds is one of the scripts available in the vistools package,

available from ESRI. For this project, the SA: Visibility script was modified to include

extra code which would save necessary data to a user specified file: This data

consisted of the x,y coordinates and elevations for the observer and target locations.

Views in the world of VRML are defined in a slightly different way: rather than being

defined by two locations representing an observer and a target, the view is described

by the following attributes:

• Position – a three dimensional vector describing translation from the

origin.

• Orientation – a three-dimensional unit vector representing the axis of

rotation plus an angle of rotation.

• Field-of-view – the preferred minimum viewing angle, in the range 0-pi.

According to the VRML97 ISO specifications, Java and JavaScript are the

recommended means of interfacing with VRML worlds. The process of modelling

responsive, dynamic events in VRML makes use of the ‘event’ concept whereby any

action within the VRML world triggers an event: these events are then routed between

‘nodes’, the building blocks of the world. A simple example of this would be a set of

traffic lights, where the light nodes would have events routed to them from a

timeSensor node, causing the lights to turn on and off in sequence according to the

events generated by the timeSensor. For this project, a slightly more complex

arrangement is required as the event which changes the position and orientation of the

observer needs to obtain values from a file output from the GIS: This is achieved by

means of a script node, which is able to change values of exposed fields within parent

nodes according to some external input. In this case, the parent node is the viewpoint

node and the exposed fields which need to be altered are position and orientation.


23

For simple scripts, it is possible to use JavaScript embedded directly within the

VRML file, but the functionality of JavaScript is limited, especially in the area of file

input/output: JavaScript does not have the capability to write to files due to the

inherent security risks associated with this in most situations in which JavaScript is

deployed. This combined with the need to process the incoming data before passing it

to the vrml-browser made JavaScript unsuitable for the task in hand: As such, a full-

blown Java program implementation was used instead.

The Java program had to provide three main functions. Firstly, the program had to

read input from the file output from the GIS; secondly, the data had to be processed;

finally, the exposed fields in the parent node had to be set to the new values. The

calculation part of the process is based on Loren Siebert’s “VRML Camera

Calculator”, a JavaScript application based on Stephen Chenney’s C code. This led to

the creation of two initial classes of object. Firstly, the CameraCalc class, based on

Loren Siebert’s work, which had methods for performing the calculations necessary,

with additional methods for choosing an input file, and reading from the input file.

Secondly, the GoScript class, which has methods for being initialised and processing

events, according to the VRML97 specification: It is this class which is instantiated

by the script node and then subsequently instantiates the CameraCalc class as part of

the processEvent() method. There are also subsidiary classes of objects needed by the

CameraCalc class: These are the Vector class, the Quaternion class and the Orient

class.


24

As a contingency measure, the observer and target locations were converted to

VRML viewpoints manually using Loren Siebert’s ‘VRML camera converter’; this

was achieved by simply using the camera converter from within the web-page from

whence it originally came. The z-value had 2m added each time to allow for the

observer/target offsets. The results of this are summarised in the table below:

In the table, the location avend is the hypothesised end of the Avenue, at Fox

Culvert while avstart is the other end of the Avenue at the Henge: This does not imply

a direction of movement along the Avenue, rather the terms are simply a means of

differentiating between each end of the Avenue.

Presentation of results;

The presentation of results will involve a number of different formats. There will

be a printed, bound write-up of the project, according to University regulations, but

there will also be a multimedia element incorporating as much of the data used in the

project as possible. This multimedia element will be based around a series of HTML

pages and will include animations rendered from the model to illustrate particular

routes as well as high-resolution still images of particular views. The CAD files and

Avenue script output filename

Obs. location (x,y,z)

Target location (x,y,z)

Orientation (x,y,z) Theta (radians) Focal Distance (m)

Silbury 2 avend

409996, 168530, 187

407545, 168733, 163.166

0.040881639172605365, 0.9983441463351585, 0.04046797569541446

1.562795088595225 2459

Avend 2 windmill

407552, 168735, 165.044

408666, 171463, 196

0.4806582348425075, -0.7200793338820061, -0.5004532087959187

1.9071559325418645 2946

Avstart 2 avend

410060, 169913, 158

407547, 168735, 165.012

-0.21286764278843428, 0.9534568797707983, -0.2135587625723392

1.6207478516012154 2775

Cove 2 silbury 408898, 169303, 166

410007, 168555, 182.145

-0.2825422250920499, -0.9150970922977689, 0.2876928965202337

1.6697325198648671 1337

Longstoneslb 2 windmill

408701, 169147, 163.498

408672, 171463, 196

0.25825318067922, 0.6703017339068092, 0.6957017178292658

2.6274083165759205 2316

Southstreet 2 avstart

409027, 169276, 166.893

410063, 169912, 158

0.2611585885319172, -0.9300930677282172, -0.25830810478947485

1.6367790838244908 1215

Windmill 2 henge

408749, 171305, 195.636

410239, 169977, 163

-0.3338701813329973, -0.8853477062082908, 0.3235585590405373

1.6785795741329381 1996


25

other files associated with the construction of the model will also be included. The

aim is to provide the reader with as much of the data used in the investigation as

possible, to allow them to replicate parts of the project or try out their own ideas:

Ideally, the whole model/GIS system would be mounted on CD for distribution

alongside the traditional bound version.

The output files from both the GIS and the reconstruction, in the form of images

and animations, are included in a series of HTML pages on the CD, allowing the user

to browse the images easily and have a reference. The VRML world is also linked to

these pages, as are links to install suitable browsers (two of which, Cortona and

CosmoPlayer are included on the CD). Finally, the 3D StudioMax files are also

included as an archive, as is the GIS. The GIS data is included as a self-extracting

archive that will install the GIS to the appropriate directory and add shortcuts to it

(Windows platforms only).


26

Results

Results of the viewshed analyses;

Starting with the cumulative viewshed analysis (see Appendix II; Figs. 10-11),

calculated using points along the path of the Beckhampton Avenue, it is clear that

certain parts of the landscape consistently fall within viewsheds (indicated by areas of

higher frequency represented by darker shades of red). These include the western side

of Waden Hill, notable for its lack of prehistoric archaeology, and Silbury Hill both of

which have very high frequency responses. Other places, such as Longstones and

South Street long-barrows and Windmill Hill’s southernmost outer bank and ditch

circuit fall within, have mid-frequency responses indicating that they fall within a

significant number of viewsheds. An interesting observation is that the enclosure in

Longstones Field sits in an area of low frequency, surrounded by an area of higher

frequency suggesting that it can be seen from fewer locations along the Avenue than

its immediate surroundings.

If we know turn to individual viewsheds calculated along the path of the avenue,

the patterns of visibility highlighted by the cumulative viewshed analysis can be

investigated in more detail (See Appendix III: Figs 12-39). As the observer moves

along the avenue, it is possible to note the changing viewshed. In particular, there are

a number of distinct phases to the changing viewshed, as detailed in the table below:


27

Phase Frames Description

A 1-5 Visibility is restricted to the section of the Avenue nearer to the Henge and to the high ground: Silbury Hill is prominent throughout, as is Waden Hill. The middle section of the Avenue is obscured including the site of Longstones enclosure and the South Street and Longstones long-barrows.

B 6-14 Visibility becomes restricted to the mid-section of the avenue, with the section nearer to the Henge gradually disappearing from view from frame 7. Silbury Hill also becomes obscured from frame 8. The end section of the Avenue beyond Longstones long-barrow is also outside of the calculated viewshed. Longstones long-barrow is tentatively close to the edge of the viewshed and may well come into view at some time during this phase; certainly is would be visible by frame 14.

C 15-20 The section of the Avenue between the Henge and Longstones Enclosure gradually disappears from sight while at the same time, the area of the valley floor to the south enters the viewshed and everything to the north, apart from the summit of Windmill Hill is obscured: By frame 18, Windmill Hill has also become obscured. Waden Hill also disappears from sight during this phase while Silbury Hill reappears when the observer reaches Longstones long-barrow (frame 18). The end section of the Avenue towards Fox Culvert is still obscured by the slight prominence over which the Avenue rises.

D 21-23 The end of the Avenue is finally revealed at Fox Culvert with South Street and Longstones long-barrows and Longstones enclosure still falling within the viewshed. The whole top of Waden Hill also becomes visible again as does the Henge as the observer rises up onto higher ground, although the Avenue between the henge and Longstones enclosure is obscured.

E 24-28 The monuments in and around Longstones Field disappear from the viewshed, as does the Henge and the majority of the Avenue, while at the same time the whole of the section of the Avenue towards Fox Culvert is exposed. Silbury Hill and Waden Hill both remain prominent.

In other words, as an observer moves along the path of the avenue, monuments

enter and leave the visibility envelope in sequence. The avenue is revealed a section at

a time and at no point is it possible to see the Avenue as a whole; rather it is revealed

as the observer moves along and around the Avenue.

Taking the viewsheds calculated from neighbouring locations into account (see

Appendix IV: Figs 40-45), it becomes clear that there are patterns of intervisibility

between the Avenue and the other monuments within the monumental complex. The

viewsheds are summarised in the table below.


28

Observer location Description of viewshed Western Henge entrance, end of the Avenue: Fig.41.

Silbury Hill, South Street long-barrow and the initial stretch of the Beckhampton Avenue are within the viewshed as are the northern slopes of Waden Hill and the southern slopes of Windmill Hill, including the causewayed enclosure. The other end of the Avenue may have passed through the viewshed: The hypothesised path runs tentatively close.

The Cove, Longstones Field: Fig.42.

The viewshed calculated from this location encompasses many of the monuments of the study region: Both Longstones and South Street long-barrows, Windmill Hill and Beckhampton enclosures, the Henge itself and the middle section of the Avenue. Waden Hill is also within the viewshed but Silbury Hill and both ends of the Beckhampton Avenue are conspicuously excluded.

Longstones long-barrow: Fig.43.

Only a small section of the Avenue is within the viewshed, although the Cove and enclosure in Longstones Field, South Street long-barrow, Windmill Hill enclosure and Silbury Hill are included. Waden Hill and the Henge are excluded.

Silbury Hill: Fig.44.

This viewshed is fairly all-encompassing: The only monuments not within the viewshed are those in Longstones Field (the Cove, enclosure and South Street long-barrow and a short middle section of the Avenue).

Windmill Hill, southern-most bank: Fig.45.

All the monuments in the study region are within the viewshed, although the Avenue is only included as far as Longstones long-barrow.

Results from the three-dimensional reconstruction;

The results from this part of the analysis are presented as series of rendered images

(see Appendix V: Figs.46-51) and animations, which can be found on the

accompanying CD. In addition there is a vrml world, originally intended to be linked

to the GIS, also found on the accompanying CD. The results support those found

using the viewshed analyses but by incorporating perspective, provide more

information regarding the view: It is interesting to note how quite large megaliths

disappear into their surroundings and are unperceivable in the rendered images

although the calculated viewshed would suggest that a line-of sight relationship exists.

If we look at the development of the monuments in Longstones Field, a number of

observations can be made. Firstly, the way in which the later Avenue respects the

earlier enclosure is quite clear (Fig. 46-7) with the Avenue running through what

would have been the entrance to the enclosure. Secondly, the way in which the initial

Cove layout was centred on the line of the Avenue is apparent, but the transition from

phase one to phase two of the Cove is interesting as the box-like arrangement is

noticeably off the centre-line of the Avenue, centred on the northern line of megaliths

instead. Indeed, there appears to be a slight shift in alignment between phases one and

two of the Cove as well, bringing the more open side of the cove in phase two, to the


29

south-east, round to be more in alignment with Silbury Hill: This is quite noticeable

from an elevated view which allows the observer to look over the intervening terrain.

Another observation is the way in which the western end of the Beckhampton

Avenue is not visible from Windmill Hill. First highlighted using the GIS, the

reconstruction confirms the way in which the Avenue moves behind a prominence

past Longstones long-barrow.


30

Discussion of results

The GIS highlighted some interesting patterns with respect to the changing

patterns of visibility associated with moving along the Beckhampton Avenue. These

were supported by the views from the three-dimensional reconstruction. As first

thought, the Avenue is positioned in such a way a to guide movement and visibility

without being restrictive. The way in which monuments enter and leave the viewsheds

calculated from points along the Avenue suggests that the Avenue may well have

been deliberately positioned to take advantage of the topography in guiding the

observers gaze. As with the southern Henge entrance at Avebury, the course of the

Avenue follows the terrain in such a way as to provide a succession of false horizons

to the observer, with monuments along the path of the Avenue exposed in sequence.

Walking from the hypothesised Fox Culvert end of the Avenue, the observer walks

over a rise and is presented with a view of the Longstones and South Street long-

barrows, the Cove and, in the distance, perhaps a brief glimpse of the Henge, although

the Avenue itself disappears again beyond the area once occupied by the

Beckhampton Enclosure. All this time, Silbury Hill rises above the horizon over on

the right. As the observer passes Longstones long-barrow, Silbury Hill becomes

obscured and more and more of Windmill Hill, with its banks and ditches, rises above

the near horizon. The end of the Avenue from whence the observer came has now

dropped out of sight and gradually the Avenue towards the Henge is revealed as the

observer continues. Having reached the area once occupied by the Beckhampton

Enclosure, the Henge gradually comes into view and on the final approach to the

Henge, the monuments in Longstones Field drop behind the near horizon. In other

words, as an observer moves through the landscape, the position of the monuments

relative to each other, the landscape and the observer, and the relationships that are

constantly formed and broken serve to produce a narrative, an experiential journey.

As regards the hypothesised section of the Avenue between the Cove in

Longstones Field and Fox Culvert, both the GIS and three-dimensional reconstruction

suggest that this section of the Avenue would also have followed the pattern exhibited

by the known section of Avenue. As with the West Kennet Avenue, the end furthest

away from the Henge curves around a prominence, resulting in a view dominated by


31

near horizons and the high ground to the south of the study region. Indeed, it is only

from this hypothesised extension to the Avenue that Silbury Hill once more comes

into view, having been obscured for much of the known path of the Avenue: Again,

this could be analogous to the West Kennet Avenue where Waden Hill obscures the

view of Silbury Hill apart from at the Henge and towards the Sanctuary.

The three-dimensional reconstruction of the cove provided a useful means of

investigating its potential development. Using the hypothesised phases for the Cove as

defined by Gillings et al (2000) and the reconstruction (see Appendix VI: Figs.46-50),

it was possible to identify the following stages in the development of the monuments

around Longstones Field:

Stage Description I Before the construction of the Avenue, the enclosure was constructed near to South

Street and Longstones long-barrows, with an entrance to the north-east towards the Henge. The area chosen for the enclosure was situated so as to only be seen from certain places in the landscape.

II The enclosure was backfilled and the Avenue constructed as far as the Cove, respecting the alignment of the enclosure entrance. Phase 1 of the Cove probably constructed during this stage.

III Phase 2 of the Cove constructed, probably shortly after Stage II. IV Avenue continuation added, heading past Longstones long-barrow, over a slight rise

and out of view.

While this is a probable sequence of development for the monuments in

Longstones Field, in reality the final three stages may well have been almost

consecutive or even contemporaneous. The apparent shifting in the Cove’s alignment

between stages II and III in order to bring it more into alignment with Silbury Hill is

an interesting observation. Although Silbury Hill cannot be seen due to the

intervening rise, and the shift in alignment is slight, it may be an archaeologically

significant observation, perhaps related to the broader patterns of visibility associated

with the full hypothesised length of the Avenue and Silbury Hill: While Silbury Hill is

visible from either end of the Avenue, it is obscured for the middle stretch through

Longstones Field where the Cove appears to be have repositioned to face it. Indeed,

the box-like arrangement open out along this alignment.

A number of issues have to be considered when interpreting the viewsheds

calculated using ArcView. Firstly, the calculation of a binary viewshed is not

necessarily the most satisfactory means of investigating visibility patterns, but given

the scope of this project and time available, it is a useful tool: As the aim was to

investigate the dynamics of the situation, how the viewshed changes, without making


32

assertions based on spatial statistics, it was felt justifiable. This will be dealt with in

full in the critique of the methodology. The binary viewsheds show quite well, when

viewed in sequence, the way in which patterns of visibility change as an observer

moves along. Secondly, they do not take into account issues such as perceivability or

vegetation cover, both of which would have had a significant influence on what an

observer would be able to see.

If we first take the evidence for the vegetation cover in the region, there is

evidence for a significant amount of clearance by the time of the mid-third

millennium BC (Malone, 1989. 34). Indeed, assuming a relatively late date for the

formalisation in stone of the Avenue, it would have been placed in countryside that

would have been cleared previously and then subsequently regenerated to a level of

scrub (ibid. 14-5). Whittle argues that by the mid-third millennium BC, there was a

phase of renewed clearance, after the regeneration mentioned by Malone (Whittle,

1993.35). If the scope of the projects had allowed, it would have been worthwhile

investigating hypotheses regarding vegetation cover in the region and how this affects

visibility based studies, particularly how vegetation may have affected the specific

observations herein noted.

The results from the three-dimensional reconstruction augmented the results of the

GIS and provided a means of testing the issue of perception. Despite the scale of the

Avenue, the stones themselves can easily blend into their surroundings when viewed

from a distance, especially if the lighting conditions are less than perfect or there is a

little fog; see the rendered images on the accompanying CD. The banks, with their

chalky texture, proved to be highly visible, as first thought. To thoroughly investigate

how the appearance of the monuments in their environmental context affected their

visibility and their visual impact, it would have been necessary to more rigorously test

different materials and environmental conditions using the three-dimensional

reconstruction; despite this, the results from the analysis were interesting and the

resultant images did serve to illustrate the effect of selected conditions on visibility.


33

Critique of the methodologies employed

The various stages of the methodology were at times rather complex, involving

many operations and a range of software. “The equivocality, heterogeneity or

multiplicity of the material world means that choices must be made in perception and

to what we attend” (Shanks & Hodder, 1995. 11). Each section will be taken in turn,

the methods and decisions made analysed and discussed in terms of their effectiveness

and how improvements could possibly be made in future. In particular, the way in

which the underpinning theoretical framework supports the use of the GIS will be

discussed, especially how the technology itself has impacted on the investigation

(Rivett, 1997. 15).

Implementing the GIS;

Implementing the GIS itself was unproblematic and performing the viewshed

calculations was not that complicated (Kvamme, 1993. 77), although a number of

caveats need to be examined. Firstly, there needs to be a discussion of the nature of

DEMs and how they affect subsequent analyses, particularly visibility based studies.

Fisher (1991. 1321) has noted how the DEM can often be the prime determinant

factor in viewshed analyses, due to the way in which line-of-sight calculations are

performed by the GIS, and due to error inherent in the DEM.


34

Figure 6; Simplified representation of a raster DEM showing positive and negative LOS vectors

The script used in ArcView performs viewshed calculations on elevation grids,

raster representations of the landscape with a fixed resolution. As such, the landscape

can be seen as being represented by an array of blocks of equal area and varying

heights (see Fig.6&7). This method of representing landscape surfaces tends to be

most effective at representing surfaces with little change in elevation: The lower the

resolution, the more rounding of elevation values occurs, producing a land-surface

with less detail. In Fig.7, the same landscape surface is represented by increasingly

higher resolution raster DEMs and it is clear how the resolution of the schematic

DEM affects lines-of-sight. Also of importance is the interpolation algorithm used to

interpolate the DEM from the original contour data. It is worth noting that the

algorithm implemented in the r.surf.contour GRASS command is known to have

problems when the distance between known values exceeds a certain limit: Due to the

use of 10m contour data, over what is effectively a region with a relatively small

elevation range, this problem became evident. Indeed, r.surf.contour uses a flood-fill

type algorithm rather than a more complex inverse distance weighting interpolation

algorithm, as found in other commands such as r.surf.idw: The use of such an

algorithm would have reduced the noticeable stepping effect in the DEM. Indeed, the

Deleted:


35

secondary products calculated from the interpolated DEM, particularly the slope map,

clearly showed the stepped nature of the DEM caused by the use of the r.surf.contour

interpolation algorithm.

Figure 7; the effects of DEM resolution on LOS vectors

In the case of this investigation, a resolution of 10m was chosen for the

interpolated DEM as the original contour data was at 10m intervals: Any higher

resolution would be most likely to represent the nature of the interpolation algorithm

rather than the actual landscape surface. As can be seen from Fig.7, if the resolution

of the DEM is not sufficient, the DEM can have adverse effects on subsequent

analyses.

Given the problems outlined above, there has to be a level of uncertainty regarding

the resultant output: The binary viewshed suggests that there are only two possible

options regarding the visibility of a given cell in the analysis which, given the

problems associated with DEM interpolation, represents a considerable simplification

of the situation. While it would have been preferable to use a technique which would

be able to take into account the error factor inherent in the DEM, such as the Monte-


36

Carlo methodology advocated by Nackaerts et al. (1997), the binary viewsheds

calculated as part of this project were indeed informative; the use of probabilistic

viewsheds should undoubtedly be considered for any future study.

As such there are two important observations to be noted: Firstly, the interpolation

stage used to produce the DEM is critical for subsequent analyses. Secondly, the

resolution of the DEM is critical for viewshed analyses. These problems have to be

accepted due to the strict time constraints set for the project, but for future

investigations the following steps would greatly improve the methodology:

• Original data – 10m interval contour data is not sufficiently detailed to create

accurate DEMs using the r.surf.contour command: It would be better to

use at least 5m contour data, obtainable from the Ordnance Survey.

Alternatively, a more sophisticated interpolation method should be used.

• Viewshed calculation – raster based elevation grids can prove unreliable for the

calculation of viewsheds, as described above. An alternative would be to

use a TIN-based system, as used for the three-dimensional reconstruction.

Unfortunately, the Avenue scripts contained in the spatial analyst

extension for ArcView calculate viewsheds using the elevation grid

approach, and it was necessary to modify existing scripts rather than write

new ones due to time constraints.

• Advanced viewshed calculation – rather than simply calculating binary

viewsheds, a better approach would be to use probabilistic or ‘fuzzy’

viewsheds. In a probabilistic viewshed, at least a hundred viewsheds are

calculated, each using a different degree of random noise applied to the

DEM within user-defined parameters: The resultant viewshed represents a

percentage chance of a given point being within the viewshed rather than a

simple in/out binary value.

These criticisms do not mean that the binary viewsheds calculated as part of this

project are meaningless; rather, the incorporation of the recommendations listed

above would have facilitated more detailed, statistical analyses of the results,

including tests to measure statistically the degree of association between the

monuments and the viewsheds. As such, the viewshed analyses conducted as part of


37

this project have been useful in identifying changing patterns of visibility within the

study region.

Constructing a three-dimensional reconstruction;

The construction of an accurate three-dimensional reconstruction proved to be less

straightforward than first imagined. The range of software needed to perform each

step of process resulted in a cumbersome methodology. Unfortunately, there was no

easy way to simplify the process: Each step provided a specific means to an end and

was essential for subsequent steps.

The production of realistic land-surfaces was quite effective, despite the number of

stages involved. The main problem was again one of resolution. The export utilities

found in ArcView and LandSerf create vrml elevation grids from the GIS dataset, bit

it of a grid or TIN arrangement. This led to vast, unusable files (greater than 100Mb)

if the export resolution was set to high or poor levels of detail if the resolution was set

too low. Eventually, this led to the definition of a smaller study region as a

compromise in order to allow a sufficiently high resolution.

A major problem involved attaching the individually modelled monuments to the

land-surface. While the process was straightforward for the individual megaliths, the

process for the more complicated monuments, such as the enclosures and Henge, was

more subjective and less controlled involving the use of a conform space and much

manual adjustment of individual vertices. This resulted in the reconstruction being

less accurate than originally desired, with the barrows being modelled as generic

forms, the Henge and enclosures being modelled as banks only. This was considered

an acceptable compromise as the banks would have been the most prominent parts of

the monuments when viewed from around the landscape, the ditches being below

ground level and, thus, out of sight from the majority of the study region. It would

have definitely been worthwhile to investigate the ditches, especially the effects of

recutting on their visibility, as this would have been a significant factor but, as already

stated, time constraints did not allow for the modelling of every possible influencing

factor; so there was a necessity for prioritisation.


38

Using scripts to provide a dynamic link;

The use of scripting to form a dynamic way of generating views proved a little too

involved for the scope of this project, resulting in a rather more manual approach. The

Java program designed did indeed function correctly, but the intricacies of vrml script

nodes were not properly resolved, particularly with the additional problem of differing

implementations of the VRML97 standard by the different browsers available. As it

was possible to achieve comparable results by more manual means, the lack of a truly

dynamic link did not prove to be too compromising; one drawback was a limit on the

number of vrml viewpoints it was possible to create manually using the output from

the GIS, given the time constraints.

Figure 8: The same scene viewed in different browsers to show inconsistencies (Goodrick, 1997)

Indeed, the quality of the exported vrml world was far from perfect. The 3D

StudioMax export utility produced a model with a number of errors, including gaps

where surfaces did not meet properly, missing planes and a complete lack of textures.

In addition, the model does not always render correctly within the browser. While the

lack of textures was purely an aesthetic fault, not affecting the use of the model as an

investigative tool, the other faults did impinge on the usefulness of the system. A

potential solution to this issue would have been to use a dedicated vrml authoring

package, such as CosmoWorlds, which, having native support for vrml, produce much


39

better results than most commercially available 3D modelling packages, which work

using proprietary formats with a conversion option.

Presentation of results;

The presentation of the results in the form of animations based on the GIS output

and rendered views from the reconstruction proved very useful. While no direct

statements could be made regarding specific lines-of-sight or locations, the more

general experiential patterns could clearly be observed. In addition to walk-throughs,

animations along paths at observer height, the animations and renders from

viewpoints that would have been impossible proved useful in spotting alignments

between the monuments.

Unfortunately, the vrml world proved a less successful way of visualizing the

spatial dataset. Without the dynamic script link, it proved time-consuming to

construct and provided little or no advantage over the use of rendered images and

animations to corroborate the GIS output.

With respect to visualizing data as part of an analytical approach rather than a

purely aesthetic one, there a number of pieces of software available as plug-ins for 3D

StudioMax which allow highly detailed models to be exported as very small files

which can be viewed in a plug-in equipped browser with little or no degradation when

compared to the original. Originally designed for selling objects over the web, the

plug-ins allow the customer to spin the object round to see all sides, zoom in and out

and pan around. In addition to this, the WildTangent software has an additional

Software Development Kit available including a full API, allowing the user to fully

customise the product and integrate it with other systems making it possible to control

the visualization and use it for analytical purposes, as was attempted in this project.

While such proprietary systems do not comply to any form of internationally agreed

standards such as the VRML97 ISO standard, they do represent a much simpler way

of achieving accurate visualisations of three-dimensional reconstructions which, due

to the Development Kit, can easily be tailored to specific needs, such as having strict

control over the viewpoints, even from another application.


40

Conclusions

To conclude, this project has certainly been an interesting one to undertake and the

various strands have led to a number of conclusions regarding both the methodology

for analysing and visualizing three-dimensional spatial data as well as the positioning

and development of elements within the Avebury complex.

Archaeologically speaking, the results of the various analyses performed served to

demonstrate the significance of movement when dealing with the Avebury complex.

Thomas (1999) has already described the effect on perception of the course of the

West Kennet Avenue, and it is hoped that the results from this investigation go some

of the way at least towards a tentative interpretation of the Beckhampton Avenue.

Barnatt (1998) writes “A site’s impact can be emphasised both by careful architecture

and by careful placing. Thus, although a distant monument is visible, sometimes

spectacularly so as a skyline feature or because of strong colour contrasts with its

surroundings, its interior is hidden by a bank or mound. At other monuments a careful

choice of site makes them invisible until the participants approach, the impact

emphasised by their sudden appearance” (ibid. 96). The results from this project have

demonstrated these factors in operation: The Henge can be viewed from a number of

locations, but the inside is only revealed in the last stretch of the Beckhampton

Avenue approaching it; the Beckhampton enclosure was placed in a depression, a

pocket of low frequency on the cumulative viewshed analysis, causing it to be

shielded from view from much of the course of the Beckhampton Avenue; Silbury

Hill appears silhouetted against the horizon for much of the course of the Avenue,

only disappearing as one approaches the Cove and the area once occupied by the

enclosure.

Such an experiential account of the patterns of visibility associated with the

Beckhampton Avenue could, in part, explain the development of monuments in and

around Longstones Field, particularly the very short primary phase of the Cove and

the destruction of the earlier enclosure: As social meanings changed over time, it

became necessary to remodel the monuments to take into account new social

interpretations. Perhaps as the Neolithic progressed and more sedentary lifestyles

became prevalent, it became necessary to formalise the ancient route-way leading


41

from the Henge using megaliths, while the values associated with the enclosure were

seen as belonging to the past and needed to be removed, at least in their present form,

from the landscape. It is interesting that Silbury Hill, which is completely obscured by

intervening terrain when viewed from Longstones Field, appears to be referenced by

the latter phase of the Cove, while along most of the hypothesised extension of the

Avenue, Silbury Hill rises up against the horizon. As the construction of Silbury Hill

reaches its third and most impressive stage between 2400-2300BC (Malone, 1989. 15)

and the lithicisation of the West Kennet Avenue and Henge takes place between

2300-2200BC (ibid.), it is not surprising that the stretch of Beckhampton Avenue

from the Henge to the Cove is roughly contemporary, constructed post-destruction of

the enclosure c. 2500-2300BC: The augmentation of Silbury Hill may well, therefore,

be directly associated with the second phase of the Cove, given that the second phase

of the Cove happened within a short period of time after the initial phase (Gillings et

al. 2000. 15). As such, the later renegotiation and rebuilding of the monuments may

well be indicative of some association with Silbury Hill but is certainly indicative of

changing social dynamics: As Bradley (1998. 99-100) argued with respect to

Stonehenge, an argument equally as applicable to Avebury, the apparent fluidity of

the sequence of development is the result of world events being interpreted in terms of

the social and monumental status quo, resulting in an almost organic evolution of

human practices and much more constrained responses to often abrupt external

stimuli. In other words, the concept of tradition is central to human action with respect

to monumental landscapes.

A number of conclusions have been drawn from the methodological approach

employed by this investigation. Firstly, while technology has now reached a level

where such projects are possible and can yield meaningful results, it has not reached a

level to make it accessible to the archaeological community as a whole. The number

of different stages needed to create a geo-referenced archaeological reconstruction,

using real-world geometry, and then to link this to the GIS proved incredible. There

was also the technical problems of support for so-called standards, particularly the

VRML97 ISO scripting standards, and available computational power. Thus, while

the project was theoretically possible, and did eventually yield positive results, the

methodology was cumbersome and, at times, there was the necessity for compromise

in order to achieve the objectives. Such compromises, such as the simplification of the


42

landscape surfaces, will have undoubtedly had an effect on the subsequent viewshed

analyses. It is possible to avoid such problems: Wood (1998) created a three-

dimensional visualization extension for the GRASS GIS, but while this has the ability

to represent spatial data using the elevation attribute to create a three-dimensional

surface onto which data layers can be draped, it does not have the ability to replicate

views or incorporate monuments or features, other than as two-dimensional drapes

over the elevation model. Woods project also involved over twenty-thousand lines of

custom written ‘C’ code.

In other words, the technology currently available can be used to investigate

problems as outlined by this investigation, not without considerable trial and error. As

new three-dimensional technologies enter the fray, including true three-dimensional

GIS, such investigations will undoubtedly become more common. Indeed, there are a

number of new three-dimensional formats becoming widely used on the world-wide-

web, including Java3D and X3D: These may well prove to be better alternatives to

VRML which, it would appear, is slowly but surely being left by the wayside as

developers adopt the ‘next big thing’. It is hoped that this investigation has shown

that, in certain circumstances, when investigating dynamic situations, the fusion of

GIS and three-dimensional technologies provides a much more informative toolkit

than either of those offered by the technologies separately. In the future, it would

certainly be worth investigating the potential of some of the other, newer

technologies, mentioned previously, for investigating archaeological hypotheses.

Referring specifically to the original aims of the project, it is thought that these

have been adequately fulfilled. The combination of the GIS and the three-dimensional

reconstruction was fairly successful, and did indeed facilitate the investigation of the

dynamic spatial relationships associated with moving along the Beckhampton

Avenue. Further to this, the methodological critique highlighted areas of weakness

and potential future lines of enquiry. As such, it is felt that while the methodology is

certainly open to further refinement, the theoretical basis is justifiable and the results

of the analysis both informative and interesting.


43

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47

Appendices

Appendix I: Elevation model images.

Figure 9: elevation map of the 'Final Study Region'

The above figure shows the area eventually chosen for the analysis: It covers an

area big enough to include the Beckhampton Avenue, the other monuments in the area

which may have been significant and possible hypotheses for the end of the Avenue.


48

Appendix II: Cumulative viewsheds.

Figure 10: Cumulative viewshed of points along the Beckhampton Avenue

The above figure shows the result of performing a cumulative viewshed analysis

using twenty-five points as observer locations along the known and hypothesised

course of the Beckhampton Avenue. The marked stepping of the resultant image is

due to the original interpolation of the DEM: The original data used was 10m interval

contour data and the interpolation algorithm used by GRASS is known to effect the

interpolation when the contours are a significant distance apart.


49

Figure 11: Cumulative viewshed, as Fig.2, post application of smoothing

This image is the result of passing a 3X3 mean filter over Fig.2. in order to reduce

the amount of distortion due to the interpolation algorithm. As the image is not to be

used for any form of statistical analysis, the effect of this mean filter will not have

adversary effects.


50

Appendix III: Frames from the Avenue viewshed animation

Figure 12: Avenue Viewshed animation - frame 1



51




52




53




54




55




56




57




58

i




59




60




61




62




63




64

Appendix IV: Viewsheds calculated from locations around the

study region.

Figure 40: Viewshed calculated from the hypothesised western end of the Avenue


65

Figure 41: Viewshed calculated from the western Henge entrance, the eastern end of the Avenue


66

Figure 42: Viewshed calculated from the Cove, Longstones Field


67

Figure 43: Viewshed calculated from Longstones long-barrow


68

Figure 44: Viewshed calculated from Silbury Hill


69

Figure 45: Viewshed calculated from the southern bank of Windmill Hill


70

Appendix V: Rendered images from the three-dimensional

reconstruction

Figure 46: The enclosure in Longstones Field

Figure 47: The Avenue and Cove, Longstones Field

These renders show the first two phases of development in Longstones Field. Both

figures have been rendered using the same camera settings to facilitate comparison, as

have the next two images.


71

Figure 48: The second phase of the Cove, Longstones Field

Figure 49: The hypothesised extension to the Avenue beyond the Cove, Longstones Field


72

Figure 50: View from atop Silbury Hill looking towards Longstones long-barrow

Figure 51: View from Windmill Hill towards Longstones Field

These images have been rendered using minimal detail in order to speed up

rendering times: Textures have been applied, but no atmospherics or object shadows

were included. The inclusion of lighting and atmospherics can multiply rendering

time by up to a hundred times.


73

Appendix VI: Maps used in the project

Figure 52: Historic OS maps of the area

Figure 53: Modern OS maps of the region

The maps used were downloaded from the Ordnance Survey website, scaled and

tiled using AutoCAD, before being exported as bitmap raster images.


74

Appendix VII: The “GoScript” Java program source code /*

This program is designed to take viewshed descriptor input from the Avenue script (007visibility), convert to vrml viewpoint type data and generate a view appropriately.

The conversion from observer-location targets to vrml orientation-rotation works fine, but the initialise() and processEvent() methods do not link to the vrml world properly. Due to browser issues and time constraints, it was not possible to get the program working :-( */ //import classes needed import javax.swing.*; import java.lang.*; import java.io.*; import vrml.*; import vrml.field.*; import vrml.node.*; /* the following classes are based on Loren Siebert's 'VRML camera calculator (available at http://www.dcs.napier.ac.uk), in turn based on Stephen Chenney's original C code (http://http.cs.berkeley.edu/~schenney) */ //allows creation of Vector objects class Vector{ //instance variables public double x,y,z; public Vector(double x,double y,double z) { //cast parameters this.x = x; this.y = y; this.z = z; } } //allows creation of Quaternion objects class Quaternion{ //declare variables public Vector v; public double r; //constructor public Quaternion(Vector v,double r){ //cast parameters this.v = v; this.r = r; } } class Orient{ //declare variables public double theta; public Vector v; //constructor public Orient(Vector v,double theta){ //cast parameters this.v = v; this.theta = theta; } } //the class that does the business class CameraCalc { public Vector obsPos; //empty constructor public CameraCalc(){ } public double vDist(Vector v1, Vector v2){

return (Math.sqrt((v1.x-v2.x)*(v1.x-v2.x) + (v1.y-v2.y)*(v1.y-v2.y) + (v1.z-v2.z)*(v1.z-v2.z)));

} public double vMod(Vector v){ return (Math.sqrt(v.x*v.x + v.y*v.y + v.z*v.z)); }


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public double vDot(Vector v1, Vector v2){ return (v1.x*v2.x + v1.y*v2.y + v1.z*v2.z); } public Vector vAdd(Vector v1, Vector v2){ Vector r = new Vector (v1.x + v2.x, v1.y + v2.y, v1.z + v2.z); return r; } public Vector vSub(Vector v1, Vector v2){ Vector r = new Vector (v1.x - v2.x, v1.y - v2.y, v1.z - v2.z); return r; } public Vector vCross(Vector v1, Vector v2){ Vector r = new Vector (v1.y * v2.z - v1.z * v2.y, v1.z * v2.x - v1.x * v2.z, v1.x * v2.y - v1.y * v2.x); return r; } public Vector vScalarMul(Vector v, double d){ Vector r = new Vector (v.x*d,v.y*d,v.z*d); return r; } public Vector vUnit(Vector v){ Vector r=vScalarMul(v,1.0/vMod(v)); return r; } public boolean checkNumber(String number){ //uses a string read in from the gis file, //hopefully with no letters (or the code will fall over) int ch; if ((number == null) || (number.length() ==0)){ return false; } for (int i=0;i<number.length();i++){ ch = Integer.parseInt(number.substring(i,i+1)); //doesn't take into account decimal points, commas, etc!! if ((ch<0) || (9<ch)) { return false; } } return true; } public Quaternion qqMul2(Vector v1, double r1, Vector v2, double r2){ double resr = r1*r2-vDot(v1,v2); Vector resv = vCross(v1,v2); Vector temp_v = vScalarMul(v1,r2); resv = vAdd(temp_v,resv); temp_v = vScalarMul(v2,r1); resv = vAdd(temp_v, resv); Quaternion resq = new Quaternion(resv,resr); return resq; } public Quaternion buildRotateQuaternion(Vector axis, double cos_angle){ double tempCosAngle = cos_angle; if ( tempCosAngle > 1.0) { tempCosAngle = 1.0; } else if ( tempCosAngle < -1.0) { tempCosAngle = -1.0; } double angle = Math.acos(tempCosAngle); double sin_half_angle = Math.sin(angle/2); double cos_half_angle = Math.cos(angle/2);

Quaternion quat = new Quaternion(vScalarMul(axis, sin_half_angle), cos_half_angle);

return quat; } public Orient quaternionToOrientation(Quaternion q){ Vector axis = new Vector(0,0,0); double half_angle = Math.acos(q.r); double sin_half_angle = Math.sin(half_angle); double angle = half_angle * 2; if (sin_half_angle < 1e-8 && sin_half_angle > -1e-8){ axis = new Vector(0,0,0); } else { sin_half_angle =1 / sin_half_angle; axis = vScalarMul(q.v, sin_half_angle);


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} Orient ori = new Orient(axis, angle); return ori; } public File chooseFile(){ //set up file chooser to choose an Arcview output file JFileChooser chooser = new JFileChooser(); chooser.setDialogTitle("Please choose an ArcView output file:"); int returnVal = chooser.showOpenDialog(null); File inputFile = null; if (returnVal == JFileChooser.APPROVE_OPTION){ inputFile = chooser.getSelectedFile(); } else {

JOptionPane.showMessageDialog(null, "ALERT!! Invalid File","ALERT!! Invalid File",JOptionPane.ERROR_MESSAGE);

this.chooseFile(); } return inputFile; } //method for creating position vectors from the txt file by reading in the data //and sending it to convertCameraModel for calculating the vrml type vector public Orient vectors2Orient(File inputFile){ //initialise br and fis outside of try-catch loop BufferedReader br= null; FileInputStream fis = null; try { fis = new FileInputStream(inputFile); br = new BufferedReader(new InputStreamReader(fis)); } catch(FileNotFoundException fnfe) {

JOptionPane.showMessageDialog(null, "ALERT!! File Not found","ALERT!! File Not found",JOptionPane.ERROR_MESSAGE);

} //initialise strings outside of try-catch loop String obsCoords = new String(""); String targCoords = new String(""); String blank = new String(""); String angle = new String(""); //readLine()'s in try-catch loop on case of IO error try{ //read: line1 observer points obsCoords = new String(br.readLine()); //read blank line separator blank = new String(br.readLine()); //read: line3 target points targCoords = new String(br.readLine());

//read: line4 angle: not used... Angle set to 360 each time in the GIS angle = new String(br.readLine()); } catch(IOException e){

JOptionPane.showMessageDialog(null, "ALERT!! IO error","ALERT!! IO error",JOptionPane.ERROR_MESSAGE);

} //parse ints int obs_x = Integer.parseInt(obsCoords.substring(8,13)); int obs_y = Integer.parseInt(obsCoords.substring(16,21)); int obs_z = Integer.parseInt(obsCoords.substring(24,26)); //create vector, adding 2m to z value to allow for offset //global variable obsPos, to be used later... obsPos = new Vector(obs_x, obs_y, obs_z+2); //parse ints int targ_x = Integer.parseInt(targCoords.substring(8,13)); int targ_y = Integer.parseInt(targCoords.substring(16,21)); int targ_z = Integer.parseInt(targCoords.substring(24,26));

//create vector, adding 2m to z value to allow for offset Vector targPos = new Vector(targ_x, targ_y, targ_z+2); //calculate using convertCameraModel Vector up = new Vector(0,1,0);


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Orient cameraOrient = this.convertCameraModel(obsPos, targPos, up); return cameraOrient; } public Orient convertCameraModel(Vector pos, Vector at, Vector up){ Vector tempv = new Vector(0.0, 0.0, 0.0); Orient ori = new Orient(tempv,0.0); Quaternion quat = new Quaternion(tempv,0.0); Quaternion norm_quat = new Quaternion(tempv,0.0); Quaternion inv_norm_quat = new Quaternion(tempv,0.0); tempv = new Vector(0.0, 1.0, 0.0); Quaternion y_quat = new Quaternion(tempv, 0.0); Vector n = vUnit(vSub(at,pos)); up = vUnit(up); Vector v = vUnit(vSub(up, vScalarMul(n, vDot(up,n)))); Vector norm_axis = new Vector(n.y, -n.x, 0); if (vDot(norm_axis, norm_axis) < 1e-8){ if (n.z > 0){ norm_quat.r = 0.0; norm_quat.v = new Vector(0,1,0); } else { norm_quat.r = 1.0; norm_quat.v = new Vector(0,0,0); } } else { norm_axis = vUnit(norm_axis); norm_quat = buildRotateQuaternion(norm_axis, -n.z); }

inv_norm_quat = new Quaternion(vScalarMul(norm_quat.v, -1), norm_quat.r); Quaternion new_y_quat = qqMul2(norm_quat.v, norm_quat.r, y_quat.v, y_quat.r); new_y_quat = qqMul2(new_y_quat.v, new_y_quat.r, inv_norm_quat.v, inv_norm_quat.r);

Vector temp_v = vCross(new_y_quat.v, v); if (vDot(temp_v, temp_v) <1.e-8){ temp_v = new Vector(0, -v.z, v.y); if (vDot(temp_v, temp_v) <1.e-8){ temp_v = new Vector(v.z,0,-v.x); } }

Quaternion rot_y_quat = buildRotateQuaternion(vUnit(temp_v), vDot(new_y_quat.v, v)); Quaternion rot_quat = qqMul2(norm_quat.v, norm_quat.r, rot_y_quat.v, rot_y_quat.r);

ori = quaternionToOrientation(rot_quat); return ori; } } public class GoScript extends Script{ //declare variables SFNode node; // field

SFVec3f pos; // translation field captured from remote transform node

SFRotation orient; //used to initialise the node, set up in the .wrl file public void initialize(){ node = (SFNode) getField("node"); } //not sure about this method yet... public void processEvent(Event e){ // get the references to the 'orientation' and 'position' // fields of the Viewpoint node

pos = (SFVec3f)((Node) node.getValue()).getExposedField("position"); orient = (SFRotation)((Node)node.getValue()).getExposedField("orientation");

//create temporary objects Vector tmp_v = new Vector(0,0,0); double tmp_theta = 10;

Orient ori = new Orient(tmp_v, tmp_theta); CameraCalc calculator = new CameraCalc(); //uses calculator to read from chosen file and convert data ori = calculator.vectors2Orient(calculator.chooseFile());


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//set exposedField values pos.setValue((float)calculator.obsPos.x, (float)calculator.obsPos.y, (float)calculator.obsPos.z); //values from calculator class global variable obsPos orient.setValue((float)ori.v.x, (float)ori.v.y, (float)ori.v.z, (float)ori.theta);

} }

Appendix VIII: the VRML code designed to house GoScript DEF myViewpoint Viewpoint{} DEF getViewpoint Script{ field SFNode node USE myViewpoint url "GoScript.class" }

Appendix IX: the customised Avenue viewshed script

The script used was a customized version of the SA: Visibility script; as such only

the additional code will be replicated here. The complete set of scripts can be found

on the accompanying CD.

'writes output to .txt file 'code taken from shp2svg by Nedjo Rogers, Environmental Mining Council of BC 'modified by Paul Cripps, University of Southampton. theView=av.GetActiveDoc theViewName=theView.GetName theViewFileName=theViewName.Substitute(" ", "_") theViewFileNameTXT=theViewFileName+".txt" theViewFileNameTXT=theViewFileNameTXT.AsFileName outputFN = FileDialog.Put(theViewFileNameTXT,"*.txt","write output text file") if (outputFN = nil) then exit end 'get the grid and interpolate z values for target and observer points s=theGrid z1=s.InterpolateZ(theLine.ReturnStart) if(z1.IsNull) then System.Beep return NIL end z2=s.InterpolateZ(theLine.ReturnEnd) if(z2.IsNull) then System.Beep return NIL end 'turn integers into strings to write to file TXTFile = LineFile.Make(outputFN, #FILE_PERM_WRITE) startZ=z1.AsString endZ=z2.AsString 'viewing angle not really needed... 'fov=lstVisList.Get(2).AsString 'write to file TXTFile.WriteElt(startZ) TXTFile.WriteElt(endZ) 'TXTFile.WriteElt(fov)


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Acknowledgements

I would like to thank firstly all the people who have provided help and

information, without which, this project would never have been completed: Graeme

Earl, Dr. Mark Gillings, Pete Glastonbury and Alligator Descartes. I would also like

to thank Dave Alexander, Tom Goskar and Anton Prowse for their help and ideas as

well as Becky Poole for her computing facilities and patience.

I would also like to thank my supervisor, Dr. David Wheatley, for his input as well

as the funding body, NERC, without whom the project could never have happened.

Education

Pathways through the Avebury Landscape; A study of spatial relationships associated with the Beckhampton Avenue, Avebury, Wilts