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RICS Practice Standards, UK 5th edition, guidance note Vertical aerial photography and digital imagery GN 61/2010

RICS Vertical aerial photography and digital imagery 2010 · 2021. 1. 29. · rics.org RICS Practice Standards, UK 5th edition, guidance note Vertical aerial photography and digital

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  • rics.org

    RICS Practice Standards, UK

    5th edition, guidance note

    Vertical aerial photographyand digital imagery5th edition, guidance note

    This combined RICS guidance note and client specification has been developedand fully updated from the 2001 4th edition of the RICS specification for Verticalaerial photography and derived digital imagery. This new fully internationalpublication recognises the shift in demand from panchromatic film andphotographic products, including digital imagery derived from those products,towards the increasing use of digital cameras and sensors in the capture ofvertical photography used in mapping projects and the use of Global NavigationSatellite Systems (GNSS) as navigational aids.

    It is intended to assist all those connected with the requesting, purchase andproduction of surveys and mapping material by advising best practice andseeking to avoid duplication of effort. This document is intended for use indrawing up clear ‘specifications’ for aerial photography and digital imageryobtained directly from digital cameras and sensors or derived from analogueaerial photography using digital scanners. The specification may be preparedby the client (the individual or organisation requesting information) or by thecontractor (those who will be tendering or undertaking the provision ofinformation).

    This document is designed as a specification for vertical aerial photographytypically required for:

    • photogrammetric mapping and digital data collection• production of orthophotography and digital mosaics • environmental information gathering and general interpretation.

    It is not a specification for remote sensing, except in the context of vertical aerialphotography and derived digital products.

    Part 1 of this document is a survey brief. Part 2 is a combined standardspecification and guidelines and covers the following:

    • Project information• Camera equipment – including calibration and digital camera specifications• Flying and photo coverage• Navigation and ground control• Digital photographic output including scanning of ‘film’ products• Digital imagery• Digital imagery product details

    Vertical aerial photographyand digital imagery

    GN 61/2010

  • Vertical aerial photography and digitalimageryRICS guidance note

    5th edition (GN 61/2010)

  • Published by the Royal Institution of Chartered Surveyors (RICS)

    Surveyor Court

    Westwood Business Park

    Coventry CV4 8JE

    UK

    www.ricsbooks.com

    No responsibility for loss or damage caused to any person acting or refraining from action as a result of the material included in this publication canbe accepted by the authors or RICS.

    Produced by the Quantity Surveying and Construction Faculty of the Royal Institution of Chartered Surveyors.

    ISBN 978 1 84219 608 3

    Royal Institution of Chartered Surveyors (RICS) November 2010. Copyright in all or part of this publication rests with RICS, and save by priorconsent of RICS, no part or parts shall be reproduced by any means electronic, mechanical, photocopying or otherwise, now known or to bedevised.

    Typeset in Great Britain by Columns Design Ltd, Reading, Berks

    Printed in Great Britain by Annodata Print Services, Dunstable, Beds

  • Contents

    RICS guidance notes 1

    Preface 2

    Introduction 3

    PART 1: THE SURVEY BRIEF 5

    1 Project information 61.1 Project designation 6

    1.2 Project contacts 82 Camera equipment 9

    2.1 Camera 92.2 Calibration 9

    3 Flying and photo coverage 10

    3.1 Flight lines 10

    3.2 Overlap 103.3 Camera orientation 113.4 Flying conditions 113.5 Airborne GNSS and inertial measurement unit (IMU) 113.6 Index plots 11

    4 Film and photographic products 12

    4.1 Scale of photography 12

    4.2 Areas to be photographed 124.3 Film type and quality 124.4 Photographic film products 124.5 Sortie and film reports 134.6 Storage and presentation 134.7 Scanning of film to obtain digital photographs 13

    5 Digital imagery 14

    5.1 Scale of photography/GSD 145.2 Areas to be photographed 145.3 Digital camera data processing 145.4 Sortie reports 14

    6 Digital imagery product details 156.1 Product details 156.2 Supply of digital imagery products 16

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | iii

  • PART 2: THE SPECIFICATION AND GUIDELINES 17

    1 Project information 182 Camera equipment 22

    2.1 Camera 222.2 Calibration 23

    3 Flying and photo coverage 24

    3.1 Flight lines 243.2 Overlap 243.3 Camera orientation 253.4 Flying conditions 253.5 Airborne GNSS and inertial measurement unit (IMU) 263.6 Index plots 26

    4 Film and photographic products 284.1 Scale of photography 28

    4.2 Areas to be photographed 284.3 Film type and quality 284.4 Photographic film products 314.5 Reports 314.6 Storage and presentation 324.7 Scanning of film to obtain ’derived’ digital imagery 34

    5 Digital imagery 36

    5.1 Scale of photography/GSD 365.2 Areas to be photographed 365.3 Digital camera data processing 365.4 Reports 37

    6 Digital imagery product details 39

    6.1 Product details 396.2 Supply of digital imagery products 40

    AppendicesA Terms and conditions 42B Glossary 43

    iv | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • RICS guidance notes

    This is a guidance note. It provides advice tomembers of RICS on aspects of the profession.Where procedures are recommended forspecific professional tasks, these are intendedto embody ‘best practice’, that is, procedureswhich in the opinion of RICS meet a highstandard of professional competence.

    Members are not required to follow the advice andrecommendations contained in the guidance note.They should, however, note the following points.

    When an allegation of professional negligence ismade against a surveyor, the court is likely to takeaccount of the contents of any relevant guidancenotes published by RICS in deciding whether or notthe surveyor has acted with reasonablecompetence.

    In the opinion of RICS, a member conforming tothe practices recommended in this guidance noteshould have at least a partial defence to anallegation of negligence by virtue of having followedthose practices. However, members have theresponsibility of deciding when it is appropriate tofollow the guidance. If it is followed in aninappropriate case, the member will not beexonerated merely because the recommendationswere found in an RICS guidance note.

    On the other hand, it does not follow that amember will be adjudged negligent if he or she hasnot followed the practices recommended in thisguidance note. It is for each individual charteredsurveyor to decide on the appropriate procedure tofollow in any professional task. However, wheremembers depart from the good practicerecommended in this guidance note, they shoulddo so only for good reason. In the event oflitigation, the court may require them to explain whythey decided not to adopt the recommendedpractice.

    In addition, guidance notes are relevant toprofessional competence in that each surveyorshould be up to date and should have informedhim or herself of guidance notes within areasonable time of their promulgation.

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 1

  • Preface

    This guidance note and client specification hasbeen developed from the fourth edition of the RICSSpecification for vertical air photography andderived digital imagery. It is part of a series ofspecifications intended to assist all thoseconnected with the requesting, purchase andproduction of surveys and mapping material at allscales by spreading good practice and seeking toavoid duplication of effort. The RICS Mapping andPositioning Practice Panel (MAPPP) is one of theforemost technical practice panels within RICS andis comprised of private and public sector surveyingand mapping industry experts, academics andsurvey instrument manufacturers. This broadexpertise enables MAPPP professional/technicalguidance and output to adhere to industry bestpractice.

    RICS and MAPPP would like to thank the followingmain authors and reviewers of this fifth edition:

    + Stuart Trigg FRICS, lead author and MAPPP –Blom Aerofilms

    + Richard Groom FRICS, lead author and MAPPP– Environment Agency

    + Dr Martin Smith FRICS – IESSG, University ofNottingham

    + Mark Breach FRICS, MAPPP – NottinghamTrent University

    + Simon Kraetor MRICS, MAPPP – BlomAerofilms

    + James Kavanagh MRICS, RICS – Director ofLand Group

    This document has been extensively reviewed bythe global surveying, mapping and imagerycommunity and by members of the RemoteSensing and Photogrammetric Society (RSPsoc).

    It is intended to be used directly, or as a model thatcould be adopted in other countries (subject to anynecessary changes to reflect local practice andlegislation).

    This document is designed as a specification forvertical aerial photography typically required forphotogrammetric mapping and digital datacollection, production of orthophotography anddigital mosaics, and environmental informationgathering and general interpretation.

    It is not a specification for remote sensing, exceptin the context of vertical aerial photography.

    It does not include the capture of obliquephotography.

    Appendix A to this document contains additionalterms and conditions of contract to be used inconjunction with the Terms and Conditions ofContract for Land Surveying Services 3rd ed 2009,published by the RICS. Other terms and conditionsmay be used if preferred. It is recommended thatthe advice of a professional survey consultantshould be sought.

    Copyright provisions are waived solely for thepurpose of using the whole or parts of thisspecification in the text of individual contracts orjob specifications.

    There are a number of other publications related tothe full range of land surveying services:

    Surveys of land, buildings and utility services atscales of 1:500 and larger: Client specificationguidelines (2nd edition 1997)

    Terms and conditions of contract for land surveyingservices (3rd edition 2009)

    2 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • Introduction

    Historical background

    The first edition of the Specification for Vertical AirPhotography was presented at the Congress of theInternational Society of Photogrammetry andRemote Sensing in 1980 and was amended as aresult of suggestions received from users anddiscussions at the ISPRS Congresses in 1980,1984 and 1988.

    Changing user requirements, technologicaladvances and experience in using the RICSspecifications under widely differing conditionsresulted in the need for substantial amendmentsand additions to the earlier documents. The needfor a new document provided the opportunity toproduce a fully international specification.

    This publication recognises the shift in demandaway from panchromatic film and photographicproducts, including digital imagery derived fromthose products, towards the increasing use ofdigital cameras and sensors in the capture ofvertical photography to be used for mappingprojects and the use of the Global NavigationSatellite Systems (GNSS) as a navigational aid,Differential GNSS (DGNSS) and InertialMeasurement Units (IMU) to provide camera stationcoordinates (which reduces the requirement forground control).

    The superseded documents held a significanttechnical content. Where possible this edition hasbeen simplified by adopting standard requirementswhich generally satisfy most user needs and byusing only a minimum of technical terms. Aglossary of these terms is included in theappendices.

    The specification

    This document is intended for use in drawing upclear specifications for aerial photography anddigital imagery obtained directly from digitalcameras and sensors or derived from analogueaerial photography using digital scanners. Thespecification may be prepared by the client (theindividual or organisation requesting information) or

    by the contractor (those who will be tendering orundertaking the provision of information). The clientis advised to undertake preparation of thespecification in conjunction with a suitably qualifiedconsultant (who may be from within the clientorganisation or an independent consultant) or withthe contractors).

    The product

    In general this series of specifications defines theproduct(s) to be delivered and not the detailedmethods to be used. Exceptions may be made inspecial cases where particular methods have asignificant effect on the quality and costs of theproduct(s). For clarity these specifications refer toboth film and digital cameras.

    Within this Specification the term ‘original image’ isused within general descriptive text to refer to thefilm exposed in the camera or the image capturedby a digital camera. The term ‘Imagery’ applies toboth analogue (film) and digital images.

    The method

    Where clients commissioning aerial photographyhave their own specialist expertise, they may wishto make amendments to this specification, but non-specialists are advised to seek expert advice beforemaking changes other than the options shown.

    The client is strongly advised to leave the choice ofthe most efficient methods to the contractor. Failureto do so may increase the costs or impair theresults. Where particular circumstances require apredetermined method to be used this should beclearly stated.

    The cameras

    The specification is based on the use of:

    + Analogue air survey cameras with a format of230 x 230mm, with either a 6” (150mm) or 12”(300mm) lens designed for photogrammetricmapping. The use of larger or smaller format

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 3

  • cameras may require substantial modificationand is considered to be outside the scope ofthis document.

    + Digital photogrammetric frame (typically, CCDarray) cameras and pushbroom sensors. [NB:the cameras must be specialist high resolutioncalibrated cameras capable of supplyingimagery for the intended purpose, ] There aretechnical differences between digital framecameras and pushbroom sensors. Each has itsown characteristics and relative advantages/disadvantages in various scenarios.

    Digital imagery

    Digital camera and sensor manufacturers havedeveloped their own systems to provide imagerywhich replicates the traditional air survey camera.Digital cameras and sensors normally directlycapture monochrome, true colour and near infraredimagery.

    The film (either colour or monochrome) fromanalogue air survey cameras may be scanned usingphotogrammetric quality calibrated scanners toproduce a digital image. The section on digitalimagery is designed to set basic standards forscanning aerial photographs.

    Digital imagery can be used to produce seamlessdigital mosaics from the monoscopic coverage ordigital orthophotography from the full stereoscopiccoverage.

    These specifications do not provide a detailedspecification for the production of digital productssuch as digital terrain models, orthophotography ororthophotos mapping. The term ‘orthoimage’ isoften used instead of orthophotography whenderived from digital imagery.

    How to use the specification andguidelines

    Part 1 of this document is a survey brief. Part 2 is acombined standard specification and guidelines.

    Part 1 is completed by the client to contain all theessential information for the project in question thatis required by a contractor to carry out the work. Itis intended that the client will edit the document inMicrosoft Word to suit his requirements. The clientmay decide to delete sections of the brief that arenot relevant for the particular project.

    *Items marked with an asterisk: indicate aninstruction, usually that the client is required to adddetail or information.

    blue text is used for defaults. The client canchange these values to suit his or her ownrequirements.

    Each section of Part 1 has a corresponding sectionin Part 2. This gives a standard specification that isintended to specify details that will always applyand give explanations in italics for the standardspecification and for options offered in Part 1.

    It will be necessary for both parties to have accessto Part 2 in order to interpret the survey briefcorrectly.

    At all stages, the contractor can advise on the mostappropriate and effective Specification for aparticular project application and can assist withthe use of this document.

    4 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • Part 1: The survey brief

    1 Project information 61.1 Project designation 6

    1.2 Project contacts 82 Camera equipment 9

    2.1 Camera 92.2 Calibration 9

    3 Flying and photo coverage 10

    3.1 Flight lines 10

    3.2 Overlap 103.3 Camera orientation Camera 113.4 Flying conditions 113.5 Airborne GNSS and inertial measurement unit (IMU) 113.6 Index plots 11

    4 Film and photographic products 12

    4.1 Scale of photography 12

    4.2 Areas to be photographed 124.3 Film type and quality 124.4 Photographic film products 124.5 Sortie and film reports 134.6 Storage and presentation 134.7 Scanning of film to obtain digital photographs 13

    5 Digital imagery 14

    5.1 Scale of photography/GSD 145.2 Areas to be photographed 145.3 Digital camera data processing 145.4 Sortie reports 14

    6 Digital imagery product details 15

    6.1 Product details 156.2 Supply of digital imagery products 16

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 5

  • 1 Project information

    1.1 Project designation

    Name…………………………………………………………………………………

    Reference No ………………………………………………………………………

    1.1.1 Purpose of project*State purpose of project and how the client will use the survey products.

    1.1.2 End product(s)Under this project the following is to be produced by the contractor:

    + original processed film (section 4)

    + film diapositives and contact prints (section 4)

    + scanned images of film (section 4.7)

    + digital photographs (section 5)

    + coordinates and attitude of camera at each exposure (section 3)

    + geocoded photographs (section 6)

    + digital mosaics (section 6)

    + digital orthophotography (section 6)

    *Delete options that do not apply.

    1.1.3 Client provisions

    Where GNSS/IMU data is required, the camera exposure coordinates shall:+ be based upon survey control stations provided by the client together with details of spheroid,

    datum and map projection. Copies are provided with these documents, or+ be based upon the national survey control framework.

    The client provides the results of previous surveys with this bid document for information. Thisinformation may not be copied or retained longer than necessary for the purpose of preparing abid or the period of any resulting contract.

    *State any additional facilities that the client will provide to assist the contractor.

    1.1.4 Project constraints

    + Photography shall be taken within 2 hours of low/high tide.+ Photography shall be taken between 1 April and 31 October.+ Photography shall be taken under lighting conditions specified in section 3.4.+ Only security cleared staff may be employed on the aircraft and/or handling films/photographic

    data.+ It is the contractor’s responsibility to obtain flight permission from air traffic control authorities.+ Contractor is to provide Health and Safety risk assessments covering work required under this

    contract.

    *State any additional constraints or specific variations to meet the contract requirements.

    6 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • 1.1.5 Proposed/estimated start and completion dates

    The project start date is *add dateCompletion date for the project is *add date

    Interim deliveries are required as follows:

    (i) Progress reportsThe contractor shall submit:

    A report at significant milestones informing the client of:

    + the intention to commence flying+ that acquisition is complete+ that photography has been checked and passed acceptance testing+ the production of derivative products has commenced/is complete

    A brief progress report at fortnightly intervals on the progress of the flying of the photographyand the production of the derivative products.

    (ii) Project report

    A Project Report shall be delivered by the contractor upon completion of the Project.

    (iii) Form of contract

    This specification is based upon Vertical aerial photography and digital imagery: clientspecification and guidelines published by RICS. To avoid misinterpretation, the client andcontractor shall refer to the full document when preparing project specifications and whenbidding for work.

    The Terms and Conditions of Contract are the current RICS Terms and conditions of contractfor land surveying services, with aerial photography appendix.

    1.1.6 Ownership and copyright

    All films exposed, and digital data acquired or created, in the contract shall:+ remain the property and copyright of the contractor+ be stored at the premises of the contractor on behalf of the client, who holds title and

    copyright of any photographic images, film, or digital data acquired or created. In returnfor the provision of such storage, the contractor shall have the right to resell the imageryunder a separate marketing agreement, or

    + become the property and copyright of the client on completion and final payment of thecontract.

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 7

  • Client organisation

    1.2 Project contacts

    The principal contact names and addresses relating to this project are given in the clauses which follow:

    1.2.1 Primary client

    Name ……………………………………… Address …………………………………Tel ………………………………………… ……………………………………………Fax ………………………………………… ……………………………………………e-mail ……………………………………… ……………………………………………

    1.2.2 Client Representative for matters concerning the Project

    Name ……………………………………… Address …………………………………Tel ………………………………………… ……………………………………………Fax ………………………………………… ……………………………………………e-mail ……………………………………… ……………………………………………

    1.2.3 Client contact for day-to-day contact Position

    Name ……………………………………… Address …………………………………Tel ………………………………………… ……………………………………………Fax ………………………………………… ……………………………………………e-mail ……………………………………… ……………………………………………

    1.2.4 Finance department for invoicing

    Name ……………………………………… Address …………………………………Tel ………………………………………… ……………………………………………Fax ………………………………………… ……………………………………………e-mail ……………………………………… ……………………………………………

    1.2.5 Others (known Local and Statutory Authorities, etc.)

    Name ……………………………………… Address …………………………………Tel ………………………………………… ……………………………………………Fax ………………………………………… ……………………………………………e-mail ……………………………………… ……………………………………………

    8 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • 2 Camera equipment

    2.1 Camera

    + For analogue film cameras a 230 x 230mm format metric air survey camera shall be used,fitted with a lens unit that of 152mm focal length and shall be colour corrected for the spectralrange of the film used.

    + For digital aerial photography a photogrammetric quality digital frame air survey camera or a‘pushbroom’ sensor capable of meeting the requirements of the contract shall be used.

    2.1.1 Restriction of image movement

    Image movement shall not exceed 25 micrometres over three or more consecutive exposures.

    2.2 Calibration

    Contractor shall supply the camera calibration certificate in accordance with the standardspecification.

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 9

  • 3 Flying and photo coverage

    Near-vertical photography shall be flown in approximately straight and level runs (strips) to achievefull stereoscopic coverage of the contract area at the nominal photo-scale.

    3.1 Flight lines

    Flight lines shall be

    either the most economical or appropriate with respect to the terrainor (a) aligned east-west

    (b) aligned north-south

    (c) a series of straight strips following a route alignment

    (d) as defined in the client specified flight plan attached

    or as defined by the client specified flight plan attached

    3.2 Overlap

    3.2.1 Frame cameras (film and digital)

    The forward overlap between successive exposures in each run shall be 60 per cent (normalstereoscopic cover).The lateral overlap (sidelap) between adjacent strips shall normally be between 15 and 35 percent.

    3.2.2 Pushbroom sensors

    Must be flown in a continuous swathe along flight lines with a minimum sidelap of 20 per cent(with 25 per cent in urban areas).

    10 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • 3.3 Camera orientation

    Camera tilt should not exceed 2 degreesCrab should not exceed 5 degrees

    3.4 Flying conditions

    The photography may be taken at any solar altitude above 15 degrees.

    3.5 Airborne GNSS and inertial measurement unit (IMU)

    GNSS is to be used for in-flight navigation and production of photo index plots.Camera exposure coordinates shall be computed from GNSS coupled with IMU observations forphoto control suitable for the project purpose. Data is to be supplied in a format suitable forphotogrammetric mapping.

    The GNSS/IMU system shall be tested by flying a test area and by comparison of neighbouringstrips of photography.

    3.6 Index plots

    Indexing of the photographs shall be by means of:

    + standard index plots

    + digital index plots in …… format (and attribute table completed as appropriate), or+ photo-indices

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 11

  • 4 Film and photographic products

    Where a film camera is to be used, this section applies. If a digital camera is to be used, seesection 5.

    4.1 Scale of photography

    Photography shall be flown at a scale of 1:3000

    4.2 Areas to be photographed

    + The area or areas to be covered by photography are defined on the contract maps suppliedwith this specification

    + The area to be covered is specified in the existing flight diagram provided by the client withthis specification, or

    + The area to be photographed is defined by the following geographic limits

    *Add details.

    4.3 Film type and quality

    The following types of film are required for this project:

    + colour negative+ colour reversal+ panchromatic negative+ colour infrared reversal, or+ black and white infrared negative.

    Quality assurance for the exposure of the file shall be obtained by sensitometric analysis andcontrol of the process. The film speed, contrast and fog shall be measured for each roll ofprocessed film.

    4.4 Photographic film products

    Contractor is to provide 2 sets of contact prints under this contract.

    Contractor is to provide 1 set of diapositives on stable based film.

    12 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • 4.5 Sortie and film reports

    The following reports are to be delivered:

    + Flight Report, as .pdf file(s)+ Flight Index, as .pdf file/text file/.dwgTwo copies of each film report shall be supplied. One copy shall be retained in the film container,and one copy shall be delivered in the project report folder.

    4.6 Storage and preservation

    While photographic materials remain in the care of the contractor they shall be stored incontainers at all times with reasonable protection against foreseeable causes of damage.

    4.7 Scanning of film to obtain digital photographs

    The original photographic images or diapositives shall be scanned.

    Scanning shall be carried out at 14µm resolution.

    All photographs shall be scanned to give stereographic cover.

    All photographs shall also be provided at a resampled resolution of 300 dpi.

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 13

  • 5 Digital imagery

    Where a digital camera system is to be used then this section applies.

    5.1 Scale of photography/GSD

    Photography shall be flown with a ground sampled distance of 4cm.

    5.2 Areas to be photographed

    + The area or areas to be covered by photography are defined on the contract maps suppliedwith this specification, or

    + The area to be photographed is defined by the following geographic limits:

    *Add details.

    5.3 Digital camera data processing

    + Contractor shall supply a copy of the data processed to level 2.

    + Contractor shall retain a copy (inc GNNS/IMU data) for security purposes.

    + Data shall be supplied as Geo-Tif data format

    + Data shall be delivered on a removable hard disk drive.

    5.4 Sortie reports

    The following reports are to be delivered:

    + Flight report, as .pdf file(s)

    + Flight index, as .pdf file/text file/.dwg

    14 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • 6 Digital imagery product details

    This section covers the production of digital photographic products from either digital cameraimages or scanned analogue photographs.

    6.1 Product details

    6.1.1 Mosaic layout

    Where specified in 1.1.2, digital mosaics shall be produced to the following user defined specification:

    + Colour/greyscale (specify) ………………………………………………………………………………………+ Scale 1: ……………………………………………………………………………………………………………+ Sheet size and layout ……………………………………………………………………………………………+ Digital data as specified in section 6.2 ………………………………………………………………………+ Hardcopy as specified in section 6.2 …………………………………………………………………………

    6.1.2 Digital orthophotography

    Where specified in 1.1.2, digital orthophotography shall be produced to the following user definedspecification:

    + colour/greyscale (specify) ………………………………………………………………………………………+ Scale 1: ……………………………………………………………………………………………………………+ output pixel size/GSD (m) ………………………………………………………………………………………+ Sheet size and layout ……………………………………………………………………………………………+ digital terrain model representing the ground surface shall be supplied by the client

    or:

    + digital terrain model representing the ground surface shall be supplied by the contractor

    + digital data as specified in section 6.2 ………………………………………………………………………+ hardcopy as specified in section 6.2 …………………………………………………………………………

    6.1.3 Radiometric values

    Imagery shall conform to the following:

    + mean histogram luminosity values shall be (see guidelines)

    + mean of the individual colour bands shall be (see guidelines)

    + standard deviation for each colour band shall be (see guidelines)

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 15

  • 6.2 Supply of digital imagery products

    The imagery produced is to be supplied in accordance with the following section which alsodescribes the data transfer medium and formats

    6.2.1 Hardcopy

    Hardcopy of the digital mosaic/orthophotography shall be supplied:+ one copy of each sheet on 60g/m2 paper+ one copy of each sheet to a photo quality of reproduction on paper of at least 100g/m2.

    6.2.2 Digital imagery

    + Contractor shall supply all deliverable digital imagery in a format which can be viewed,manipulated and plotted using (state name of GIS/image viewing/editing software packagename).

    + The contractor shall investigate and recommend viewer software to display, manipulate andplot the deliverable digital imagery on the client computer system.

    6.2.3 Data format

    Data format shall be Geo-Tif.

    6.2.4 Compression

    Data shall be compressed using .jpg.

    6.2.5 Transfer medium

    The data shall be supplied on removable hard-drive.

    With interim (part) deliveries on DVD.

    16 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • Part 2: The specification and guidelines

    1 Project information 182 Camera equipment 22

    2.1 Camera 222.2 Calibration 23

    3 Flying and photo coverage 24

    3.1 Flight lines 243.2 Overlap 243.3 Camera orientation 253.4 Flying conditions 253.5 Airborne GNSS and inertial measurement unit (IMU) 263.6 Index plots 26

    4 Film and photographic products 284.1 Scale of photography 28

    4.2 Areas to be photographed 284.3 Film type and quality 284.4 Photographic film products 314.5 Sortie and film reports 314.6 Storage and presentation 324.7 Scanning of film to obtain digital photographs 34

    5 Digital imagery 36

    5.1 Scale of photography/GSD 365.2 Areas to be photographed 365.3 Digital camera data processing 365.4 Sortie reports 37

    6 Digital imagery product details 39

    6.1 Product details 396.2 Supply of digital imagery products 40

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 17

  • 1 Project information

    Section 1 enables the client to summarise thepurpose of the project and the work to beundertaken, to provide details of the contactswithin the client organisation and to specifyconstraints.

    1.1.1 Purpose of project

    This information is crucial in guiding the contractorin their interpretation of the requirement and thespecification. The photography needs to be fit forpurpose and may be required for one or more usesincluding photogrammetric mapping, rasterscanning, digital orthophotomapping, land use andland cover interpretation.

    1.1.2 End product

    The derived product scale or required resolution,ground sample distance (GSD) will be the largestscale at which the data provided will be used foraccurate purposes. If this is not compatible withthe requested photographic scale then thecontractor may suggest alternative options to theclient.

    Under this project the following is to be producedby the contractor:

    + original processed film (section 4)

    + film diapositives and contact prints (section 4)

    + scanned images of film (section 4.7)

    + digital photographs (section 5)

    + coordinates and attitude of camera at eachexposure (section 3)

    + geocoded photographs (section 6)

    + digital mosaics (section 6)

    + digital orthophotography (section 6)

    *Select the options.

    1.1.3 Client provisions

    It is possible to obtain the coordinates andelevation of each camera exposure position usingGNSS/IMU observations. These are covered in

    section 3.5 of this specification. The options in thissection concern the coordinate system to be used.

    Option – where GNSS/IMU data is required, thecamera exposure coordinates shall be based uponsurvey control stations provided by the clienttogether with details of spheroid, datum and mapprojection. Copies are provided with thesedocuments. (Note: is required if subsequentmapping has to fit with an existing client-specifiedsurvey control systems for which the client hassurvey control stations).

    Option – the camera exposure coordinates shall bebased upon the national survey control framework.(Note: is required where the national survey controlframework is to be used and the contractor is toobtain the data he needs from a third party – e.g.the national mapping agency).

    The client provides the results of previous surveyswith this bid document for information. Thisinformation may not be copied or retained longerthan necessary for the purpose of preparing a bidor the period of any resulting contract. (Note: Thisis information that may be helpful for biddingpurposes. The client should also supply anyadjacent or overlapping surveys which may beneeded by the contractor for edge matching or tomaintain consistency with previous work).

    *The client should include here any other facilitiesthat will be made available.

    1.1.4 Project constraints

    Provide information on any restrictions to the work,such as:

    + Security clearances required – in someinstances this is required to fly over,photograph, and process data of particularlocations or to be able to operate in certaincountries.

    + Air Traffic Control requirements – this is requiredfor any project but may be difficult to obtain orwill be restricted in areas of high traffic such asapproaches to major airports, military trainingareas, or in certain countries.

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  • + Special requirements for flying – such assummer/winter photography. The ‘normal’ flyingseason in the northern hemisphere is from Aprilto October as this gives the greatestopportunity to capture the photography inoptimal lighting and weather conditions.

    + Special requirements for state of tides – high/low/normal/spring, etc. along with the limitseither side. Also include the harbour or localtide tables to be used in calculating the timingsor, if the tidal state is difficult to calculate fromtables, where for example particular harbours/estuaries in the target area may be slow indraining, and the client has specific detailedknowledge, then the client should specify thetidal window along with a buffer amount.

    + Requirements for minimum sun angles – thesemust take into account and be flexible to allowfor the capture of seasonal (e.g. winter)photography and tidal window requirements.

    + Special limitations relating to dates or times offlying – but not related to the quality ofphotography (such as religious days).

    + Health and Safety/Environmental requirements –some clients may require Risk Assessments tobe provided for example low level flights overareas of scientific interest or areas whichprovide a high risk of bird strikes over estuariesor nature reserves.

    See also 3.4.1 below.

    1.1.5 Proposed/estimated start date

    Realistic start and completion dates should bestated. Allowance needs to be made for the timerequired to mobilise the aircraft and considerationshould be given to the likely weather conditions,which may preclude flying at certain times of theyear.

    1.1.6 Progress reports

    The contractor shall submit a brief progress reportat regular intervals on the flying of the photographyand of production of the derivative products.

    Clients may also request that they be informed ofprogress at significant milestones, e.g. immediatelyprior to the commencement of flying, oncompletion of flying and when the photographydata has been checked to confirm that specifiedtimes/windows/quality requirements are being met.The time between the acquisition and qualityacceptance of photography/data should be kept toa minimum in case it is subsequently rejected andthere is a need to refly, which could compromisetime or project constraints.

    The method and format of reporting by thecontractor should be agreed by the client. See alsobelow.

    1.1.7 Project report

    A project report shall be delivered by the contractorupon completion of the project.

    See also 4.5 and 5.4 below.

    1.1.8 Form of contract

    It is recommended that the RICS Terms andconditions of contract for land surveying services,together with the Aerial Photography Appendixfrom this document are used. If different terms andconditions are required they should be specified.

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  • 1.1.9 Ownership and copyright

    Under this section the client must now decide ifthey wish to retain control of the original films. Thefilms are then delivered to the client unless aseparate contract is entered in to regarding thestorage of the films by the contractor.

    In the case of material which has security sensitivityit is expected that the film would be delivered tothe client. In most other cases the contractor willhave better facilities for the handling, storage andsubsequent reproduction of the film.

    All films exposed, and digital data acquired orcreated, in the contract shall:

    either (a) remain the property and copyright ofthe contractor

    or (b) be stored at the premises of thecontractor on behalf of the client, whoholds title and copyright of anyphotographic images, film, or digitaldata acquire or created. In return forthe provision of such storage, thecontractor shall have the right to resellthe imagery under a separatemarketing agreement

    or (c) become the property and copyright ofthe client on completion and finalpayment of the contract.

    Where option (b) is selected it will be necessary toprovide a separate agreement for royalty payments.The storage and conservation of archivephotography is a specialist activity and the cost ofsuch maintenance has to be considered whenarriving at the rates for royalty payments.

    Where option (c) is selected the client shouldensure that adequate facilities for the storage of thefilms are available, if the value of the investmentmade is to be maintained. Films have to be kept ina controlled environment or will deteriorate.

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  • Client organisation

    1.2 Project contacts

    Providing information on the essential contacts ofthe project avoids unnecessary delays. On anyproject an individual or organisation may act in oneor more of the following capacities.

    1.2.1 Primary client

    The primary client organisation is the individual ororganisation whose proposals generated therequest for the survey information and who will bethe source of the project’s finance.

    1.2.2 Client representative

    The client representative is the individual ororganisation who is responsible for mattersconcerning the project and the management of thetask.

    1.2.3 Client contact

    The client contact is the individual with whom day-to-day contact is made.

    1.2.4 Finance department

    The finance department, to whom invoices are tobe addressed, should be clearly indicated.

    1.2.5 Others

    When appropriate, the contact information for Localand Statutory Authorities should be provided. Thisclause should be repeated as necessary to ensurea separate entry is supplied for each essentialcontact.

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  • 2 Camera equipment

    2.1 Camera

    The requirements will be either:

    A 230 x 230mm format metric air surveycamera shall be used, fitted with a lens unit thatis designed to give a residual distortion notexceeding 5 micrometres except in the cornersof the image. The lens will normally be of152mm focal length and shall be colourcorrected for the spectral range of the filmused. A film flattening device shall be used tomaintain sharp focus and hold image distortionwithin the limits specified in clause 4.2.Exposed surfaces of the lens unit should becleaned regularly in accordance with themanufacturer’s recommendations.

    or:

    A photogrammetric quality digital frame airsurvey camera or a ‘pushbroom’ sensorcapable of meeting the requirements of thecontract.

    The term ‘metric’ is used to identify a film camerawhich has been specifically made or modified forphotogrammetry. It will provide a largely distortionfree image, which can be calibrated by means ofinbuilt marks (fiducial marks) which appear on eachimage. The universal size used for air survey is the230 x 230mm format. Other sizes of metric cameraexist but these are largely designed for groundbased photogrammetric applications. Some may besuitable for certain types of air survey work, buttheir use might require substantial alteration to thisspecification.

    The typical multi-purpose lens in use is one of150mm. However, a lens with an alternative focallength of 88mm (a wide angle lens giving betterheight precision), 210mm or 306mm (a long focallength giving better detail definition in urban areas)may be selected by the contractor if the project orarea conditions make this desirable.

    Digital cameras may also be ‘metric’ in that theyare factory calibrated and the calibrationparameters must be used to remove distortions inthe assembled digital images. Normally, digital

    frame cameras will use multi CCD arrays in theirconstruction and the images from the individualCCDs are ‘stitched’ together by the processingsoftware to form a larger image or ‘footprint’ on theground. Whilst medium or small format camerasmay make use of high definition CCDs, a reducednumber of CCDs may make the use of medium andsmall format cameras impractical for large surveytasks due to the smaller footprint and moreswathes or strips of photography to be flown for aparticular task.

    2.1.1 Restriction of image movement

    Image movement shall not exceed 25 micrometresover three or more consecutive exposures. Thismay require the use of a camera with forward-motion compensation (FMC) and a gyro-stabilisedmount during turbulent conditions.

    Most current air survey cameras offer forward-motion compensation (FMC). This mechanismremoves most of the image movement due to theflight of the aircraft over the ground but cannotremove random image movement due to rotationsof the aircraft caused by turbulence. Theimprovement in image quality is very significant atlarge scales but has less benefit at small scales.The speed of the aircraft, the exposure time, andthe scale of the photography, determine the amountof image movement.

    [Note: analogue (film) cameras will have amechanical FMC system, digital cameras may havedigital processing software that will remove imagemovement]

    Gyro-stabilised camera mounts are designed toreduce camera tilts and sudden rotations.

    The contractor will select the equipment necessaryto provide the product quality required under theflying conditions at the time of photography.Significant image movement degrades the qualityand subsequent obtainable accuracy.

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  • 2.2 Calibration

    Each camera lens unit to be used on the contractwill have been calibrated, cleaned, tested andcertified by the camera manufacturer or by acalibration centre, recognised internationally orapproved by the camera manufacturer, within twoyears prior to the date of the photography. Themeasured distortion shall fall within the limit definedby the manufacturer for the lens type.

    The calibration certificate shall contain the followinginformation:

    + name and address of the calibration centre andname of authorised signatory

    + date of calibration

    + camera manufacturer’s serial number of thelens unit

    + calibrated focal length of the lens unit inaccordance with the manufacturer’srecommendations

    + radial distortion in micrometres

    + position of the principal point of autocollimationor of best symmetry with respect to the imagecoordinate system.

    If the contractor becomes aware of any causewhich may affect the calibration of the camera theclient should be informed immediately.

    The calibration period for camera lenses is nowspecified to be two years, recognising that modernlenses remain very stable and that the cost of anannual recalibration within countries without locallaboratories may be considered excessive. Whenthe contractor already has a camera on location forother work it would be permissible to accept ashort extension to the period of calibration iffacilities were not readily available locally forrecalibration.

    Digital cameras are calibrated and ‘electronicallyadjusted’ by the manufacturer to bring the systemto a ‘zero’ state or within the manufacturedtolerances as sated on the calibration certificate.The calibration data file which is produced duringthe calibration process is used in the first stages ofimage data processing. This data file would notnormally be provided to the client unless the supplyof raw data is specified as part of the contract.

    Aerial Survey Cameras, both analogue and digital,may have a GNSS and an inertial measurement unit(IMU) which will also require calibrating along withthe associated camera (see section 3.5)

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  • 3 Flying and photo coverage

    Near-vertical photography shall be flown inapproximately straight and level runs (strips) toachieve full stereoscopic coverage of the contractarea at the nominal photo-scale.

    Since there is little cost saving to be obtained byreducing the overlaps between exposures to aminimum, it is strongly recommended that near-vertical photography is flown to achievestereoscopic coverage. This will maximiseopportunities for future use.

    3.1 Flight lines

    Flight lines shall

    either: be prepared by the contractor and be:or (a) the most economical or appropriate

    with respect to the terrain

    or (b) aligned east-west

    or (c) aligned north-south

    or (d) as defined in flight plan attached

    or (e) a series of straight strips following aroute alignment.

    or Where a few exposures in a run arerejected for any reason, they may bereplaced by a short filler run, providedan overlap of at least twostereoscopic models is supplied atboth ends of the run

    Or be defined by the client in an attachedflight diagram.

    *Select the option required.

    The general alignment of the dominant relief to themapping area may determine the choice of option(b), (c) or (d). Option (e) will be chosen when a longnarrow area is required. Option (a) may be chosenfor an irregular area or series of areas when there isno requirement by the client for specific orientationof the photography. Once the minimum number ofruns required to cover the target area has beencalculated, the spacing between flight lines may beadjusted to increase and equalise the lateraloverlap between each run.

    There should be no duplicate run/strip or framenumbers. The sequence should be maintained evenif the target area is subsequently flown in severalflights/sorties.

    Clients may provide their own existing flightdiagram. This is extremely helpful when there is arequirement for an on-going repeat or monitoringsurvey (e.g. year on year), which may be inprogress, to ensure that flight runs and individualframes are maintained over several epochs.Contractors should then comply with the positionof exposures according to the flight diagram, andmaintain existing frame and run numbers fromprevious epochs.

    3.2 Overlap

    3.2.1 Frame cameras (film and digital)

    The forward overlap between successive exposuresin each run shall be:

    either (a) 60 per cent (normal stereoscopiccover)

    or (b) per cent (greater percentage,dependant upon purpose)

    or (c) pinpoint.

    An allowance of ± 5 per cent of the selectedoverlap is permissible.

    The lateral overlap (sidelap) between adjacent stripsshall normally be between 15 and 35 per cent forflying heights greater than 1,500 metres abovemean ground level, increasing to between 20 and40 per cent for lower flying heights.

    Where ground heights within the area of overlapvary by more than 10 per cent of the flying height,a reasonable variation in the stated overlaps shallbe permitted, provided the forward overlap doesnot fall below the selected percentage and thelateral overlap does not fall below 10 per cent orexceed 45 per cent.

    In mountainous areas, where it is impossible tomaintain the lateral overlap specified above, short

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  • infill runs shall be flown, parallel to and betweenthe main runs, to fill the gaps.

    In coastal areas where a run crosses the shorelinethe forward overlap shall be increased to a 90 percent overlap. The increase in overlap shouldinclude at least three photo-centres over land.

    Film cameras have a square format, Some digitalframe cameras may have a rectangular (not square)format but the same principles apply. The usualfore and aft overlap to give stereo coverage is 55%and sidelap is normally 20%.

    The forward overlap is required to ensure adequateformation of stereoscopic coverage. The lateraloverlap is required only to ensure that no areas aremissed between adjacent flying strips. Wheresubstantial changes of height occur across the pathof the flight lines the lateral overlap may be lostand infill runs may be needed.

    80% fore and aft overlap and 25% sidelap wouldnormally be selected for the production oforthoimages of urban areas with high rise buildings.By increasing the coverage each tall building willappear in more frames, thus increasing the choiceof images which show the building to appearvertical. Exceptionally, the sidelap may beincreased to 60% (along with a fore and aft overlapof 80%) by clients who intend to use imagery forthe production of 3D city models.

    A client may also specify a precise position for thecentre point of an image, along with a requiredphoto scale or GSD.

    Photo or image centres may be defined usingairborne GNSS positioning.

    The proposed flight lines are calculated in advanceon the basis of minimum overlap. This usuallyresults in the final run covering an area mainlyoutside the contract area. The spacing of all runs isadjusted to distribute the ‘spare’ coverage equallybetween all the runs.

    3.2.2 Pushbroom sensors

    Must be flown in a continuous swathe along flightlines with a minimum sidelap of 20% (with 25% inurban areas).

    Pushbroom sensors acquire multiple strips ofimages simultaneously (forward, nadir andbackward) as apposed to a series of separate

    exposures. Stereo viewing is derived from the fixedgeometry of the sensor. Scanner based imagerymust therefore be flown in a continuous swathewith a minimum 20% sidelap (25% in elevated orurban areas).

    3.3 Camera orientation

    Excessive tilt and crab should be avoided as it canresult in loss of overlap between exposures.Turbulent weather conditions and strong crosswinds are the primary cause.

    Camera tilt should not normally exceed 2 degrees.An occasional exposure with up to 4 degrees maybe permitted, provided the minimum forward andlateral overlaps are maintained.

    Crab shall not exceed 5 degrees, as measuredbetween the base line and a line parallel to theframe of the negative, provided the minimumforward and lateral overlaps are maintained.

    3.4 Flying conditions

    The photography may be taken at any solar altitudeabove 15 degrees, unless special restrictions areincluded.

    The photography shall only be flown in conditionswhen the visibility does not significantly impair thetone reproduction in the negative or digital imageand detail is not lost as a result of atmospherichaze, dust, smoke, or any other conditionsdetrimental to the photographic image.

    The photography shall be substantially free ofcloud, dense shadow or smoke. Isolated areas ofcloud, dense shadow or smoke shall not be causefor rejection of the photography provided theintended use is not impaired.

    Weather and atmospheric conditions are outsidethe control of the contractor.

    The ‘normal’ flying season in the Northernhemisphere is from April to October to take theopportunity of capturing photography in optimallighting and weather conditions. The need foradherence to a contract requirements and acompletion date must be tempered by the need toproduce an acceptable product.

    Some contracts may specify maximum amounts ofcloud/haze, e.g. 5% on any individual photographframe or 2% of total photography flown.

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  • Some contracts may stipulate the minimum sunangle, e.g. 15 or 20 degrees. Low sun angles mayresult in deep shadows particularly in urban areasor where there are considerable differences in theheight of the terrain.

    While digital systems can accommodate poor lightconditions and are more tolerant of deep shadows,specific requirements will limit the time of day andtime of year effectively available for the acquisitionof imagery.

    3.4.1 Timing and special conditions forphotography

    The photography may be flown at any time whenthe weather conditions and sun altitude are suitableto achieve the specified standards of image quality,except where special time constraints are defined.

    The intended use of the photography may imposelimitations upon times of flying examples being:

    + Winter/seasonal photography; acquiringphotographs when trees are not in leaf, there isno snow cover, or the state of crops, vegetationcover.

    + Coastal photography; flying at high/low/normal/spring tides or at specified tidal windows.

    + Specific dates or time of events; for measuringcrowd/traffic density at sport events/festivals,the extent of flooding.

    Other limitations might include restricted use ofairspace/air traffic control requirement or religious/public holidays. See also 1.1.4.

    3.5 Airborne GNSS and inertialmeasurement unit (IMU)

    either GNSS is to be used for in-flight navigationand production of photo index plots

    or GNSS coupled with observations from aninertial measurement unit is:

    either (a) not required for this project

    or (b) to be used for in-flight navigation andfor photo control purposes.

    The camera station coordinates supplied will befor use as photo-control on 1:…… scalemapping.

    They shall be given in the

    …………grid referencing system applied to the

    ………… geodetic datum.

    The accuracy of camera station plan and heightcoordinates, for not less than 95 per cent of thevalues, relative to the geodetic referencing systemdefined above shall be better than ± 20 centimetreswhen used for photo-control and ±100 metreswhen used only for the provision of the index plot.

    If GNSS/IMU systems are specified to be used,evidence must be provided that the GNSS andassociated IMU and camera are calibrated on a testarea at regular intervals, particularly when thecamera may have been removed and re-installed inthe aircraft, to provide angular misalignments whichare then applied to the data when producingpositioning and exterior orientation files.

    The contract may specify if a test is flown in thevicinity of the flying target area.

    Note: the descriptive term Inertial NavigationSystem (INS) may be used as an alternate toInertial Measurement Unit (IMU).

    The use of GNSS aided IMU direct georeferencingsystems make for significant savings in the amountof ground control and air triangulation effortrequired to provide accurate positioning of imageryboth for a subsequent mapping project and for theproduction of digital orthophotos or orthomosaics.

    The contractor will normally decide if airborneGNSS is to be used and must state if the GNSSdata, along with base station data, is required to bedelivered as part of the contract. However thecollection and supply of such data should now beconsidered as a standard practice and be includedin the costs of the contract (see section 6.5).

    3.6 Index plots

    Indexing of the photographs shall be by means of

    either:

    (a) standard index plots, or

    (b) photo-indices

    or

    (c) digital index plots

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  • (a) standard index plots

    Index plot(s) of the photography shall be supplied,based on topographical maps to be provided bythe client. The contractor shall supply one set oftransparent overlays with folded paper copiesenclosed in the Project Report and with each set ofcontact prints delivered.

    The index plots shall indicate the position ofalternate exposures with sufficient exposurenumbers annotated for identification with noduplication in run or frame numbers.

    Index plots shall contain the following information:

    + scale, grid system, grid North and grid valuesof the base map

    + Client’s name

    + Contractor’s name and address

    + name of project or contract area

    + boundary of contract area

    + dates of photography

    + nominal scale of photography

    + camera manufacturer, type and focal length oflens unit

    + film numbers and run (strip) numbers at bothedges of each sheet and where changes occurwithin a sheet

    + positions and numbers of selected individualexposures.

    Sheets to be numbered if more than one is withinthe project.

    Where the client holds copyright or a licence toreproduce the base mapping the index plots maybe incorporated into a master transparency. Inother situations the index plot shall consist of anoverlay at the map scale, with paper copies madefrom the overlay superimposed upon the base map.

    (b) digital index plots

    Standard index plots overlay a topographical mapprovided by the client. A digital index plot isintended to overlay the equivalent raster data andto act as a further layer within the GIS system.Proper integration into the client system will enabledetails to be recalled by clicking on the photoimage.

    If required, the index plot(s) shall be supplied as adigital file suitable for use in a geographicinformation system (GIS). The content and titleinformation shall be as specified. The cartographicpresentation shall be suitable to use as an overlayto the topographical base map provided. Theattribute table should also be completed asappropriate. The data format and transfer mediumshall be agreed with the client.

    (c) photo-indices

    A photo-index is a simple non-matched mosaicprint which acts as an index. It may be specifiedwhen appropriate mapping is not available for usewith the other indexing options.

    If required, a photo-index shall be supplied insteadof a map-based index plot. These shall be suppliedat a reduced scale using the first, last and alternateprints, which shall be trimmed to the edge of thephotographic image. The photo-number shall beclearly marked on the first and last print and onevery fifth print. The content and title informationshall be as specified.

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  • 4 Film and photographic products

    Where a film camera is to be used, this sectionapplies. If a digital camera is to be used, seesection 5.

    4.1 Scale of photography

    The requirements are normally stated as:

    + either: The principal scale(s) of photography tobe provided for this Project is 1: ………or

    + The Ground Sample Distance (GSD) of thedigital imagery is required to be: ……cm

    The photograph scale is normally quoted foranalogue film cameras and is dependent upon thecamera format, focal length of the lens and theflying height.

    In most cases the film will be scanned. Scanningresolutions are typically between 10 and 25 micronsand a ground sampling distance (GSD) is createdfor each digital pixel.

    The parameters for digital cameras relate to thepixel size of the CCD array and the GSD is afunction of pixel size, the focal length of the cameraand flying height. It is normal for output to bequoted as a GSD rather than photographic scale.

    Table relating film scale, digital imagery resolutionto potential photogrammetric mapping scale andaccuracy

    PhotoScale

    GSD MappingScale

    HzRMSE

    VerticalRMSE

    1:3000 4cm 1:500 +/-0.100m

    +/-0.050m

    1:5000 7.5cm 1:1250 +/-0.225m

    +/-0.125m

    1:10000 15cm 1:2500 +/-0.500m

    +/-0.250m

    Other scales may be used for specialist products.Some clients may have their own specificstandards.

    4.2 Areas to be photographed

    The client should clearly define the boundary forphotography, preferably by a map or by the supplyof a digital file to assist flight planning. Care isrequired in the preparation of such a map andfailure to do so can lead to insufficient coverage. Itis important not to mark beyond the required limits,since this will result in unnecessary photographyand increases costs.

    The client may provide their own or existing flightdiagram which will define the area of photography,flight runs/strips required and the position ofspecific frames/exposures. This is extremely helpfulwhen the contract is part of a repeat or an on-going monitoring survey involving different epochsof time, in which case it could be important, fromthe client’s point of view, to adhere to the existingflight diagram.

    4.3 Film type and quality

    All film used shall be within the manufacturer’srecommended expiry date and kept in accordancewith the manufacturer’s recommended storageconditions. When specified for use, colour infraredfilm shall be thawed 24 hours before use.

    The following types of film are required for thisProject:

    + colour negative (masked or unmasked)

    + colour reversal (or processed to a colournegative)

    + panchromatic (black and white) negative

    + colour infrared reversal

    + black and white infrared negative.

    *Delete any of the options not required. Theintended use will determine the film type to beused.

    Colour negative film is now used as the generalpurpose film for most applications. It enables theprovision of natural colour photography andimagery and assists in the interpretation of detail,both by visual inspection and during the process ofphotogrammetric plotting.

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  • Colour infrared film is particularly advantageous invegetation studies where it is required to record thedifferences within healthy vegetation. Thealternative for such use is black and white infraredfilm, but the tonal contrasts provided are lessprominent.

    Colour diapositives can generally be produced togood quality from colour negatives. Directtransparency (colour reversal) film has lessexposure tolerance than negative film and istherefore more likely to produce a slightly degradedimage, if incorrectly exposed or processed.

    4.3.1 Metric quality of original films

    A stable base film shall be used and the processingand drying of the film shall be carried out withoutaffecting its dimensional stability. In any originalimage the differential lengths between any pairs offiducial marks shall not exceed 15 micrometres.Original images and diapositives shall not containresidual y-parallaxes after relative orientation inexcess of 15 micrometres anywhere in the model.

    All film intended for air photography ismanufactured with a suitable stable base. Theprocessing must be carried out with care in orderthat subsequent distortions are not created. Limitsare given for variations which can be measuredbetween the fiducial marks imprinted onto the filmby the camera. Refer to the notes for clause 2.

    4.3.2 Image quality of original films

    The image quality of the processed film shall be ofa standard that allows the production of prints ordiapositives suitable for the intended application asstated in clause 1.1.1. Such products will have astandard of tone and colour reproduction (ifappropriate), together with a level of detailthroughout the image to ensure suitability forpurpose.

    Processing of the film shall be monitored bysensitometric analysis and records of the resultsshall be included with the film report.

    All processed film used for the work shall besubstantially free of blisters, bubbles, inclusions,coating lines, stress or static marks, bar marks, pinholes, abrasions, streaks, chemical marks, dryingmarks or scratches.

    Image quality is comprised of tone/colourreproduction and the degree of small detail visiblein the image. The quality is dependent upon thedegree of control exercised over storage, exposureand processing of the film.

    A high standard of quality assurance should bemaintained in film processing. This is necessary inorder to provide a satisfactory basis for tone/colourreproduction in particular and to achieve goodspatial resolution. Quality assurance can beprovided by sensitometric analysis and processcontrol. It may also include an assessment ofmicro-image detail in the photography.

    Physical damage to the film should always beavoided. Refer also to the notes for clause 4.6.

    4.3.3 Process control records

    Quality assurance for the exposure and processingof the film shall be obtained by sensitometricanalysis and control of the process. The film speed,contrast and fog shall be measured for each roll ofprocessed film. These characteristics are to bedetermined from sensitometric exposures made onan area of the leader and/or trailer of the film that isclear of any other exposure. There shall be not lessthan three such sensitometric exposures made perfilm to ensure that at least one is suitable formeasurement.

    The contractor may process such controlexposures in advance of the main film in order tofacilitate fine adjustment of the processing to obtainoptimum results.

    The determination of the film characteristics shalltake into account the individual sensitive layerswhen processing colour material. Within the usablerange of densities the characteristic curves shouldremain substantially parallel.

    Sensitometric exposures are made on the leader ortrailer of the film to be processed, in an area whichhas not otherwise been exposed. After processingthe densities in each step of the sensitometricexposure (either monochrome or RGB) aremeasured and recorded. When the values areplotted in the form of D/log(io)H the resultantcharacteristic curves can be used to determine thefilm speed, contrast and fog level.

    The test section of film can be cut from the mainfilm and processed in advance as part of the

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  • contractor’s normal quality control or may remainas part of the film, when it acts as a record of theprocessed film.

    The sensitometer used to produce the grey scaleexposures used for measurement should have aspectral output similar to the irradiation received atthe surface of the earth from the sun, over therange 380 to 900nm. The sensitometer shouldprovide a single exposure comprising varying levelsof irradiance by use of a calibrated step wedge.The step wedge should have a uniform spectraltransmission over the range 380 to 900nm.

    4.3.4 Film speed

    The sensitivity of the film shall be measured by aprocedure that is in general agreement with anappropriate national or international sensitometricstandard for the determination of film speed inrelation to aerial photography either:

    either (a) Relative film speed shall bedetermined

    or (b) It is necessary that absolute filmspeed be determined.

    *Select the option required.

    Absolute film speed determination would only berequired in exceptional circumstances. For suchdeterminations a sensitometer with a calibratedradiant source must be used.

    4.3.5 Film contrast

    The conditions of development shall ensure astandard of contrast in the original image that,when printed using an automatic dodging printer,will provide sufficient detail in areas of both cloudshadow and very reflective terrain to meet theneeds of the application.

    Contrast should be measured as the averagegradient of the characteristic curve determined fromthe sensitometric exposures, in accordance with anappropriate national or international sensitometricstandard.

    4.3.6 Base plus fog density

    The base plus fog density shall be measured in anunexposed area of the processed film. It shall notnormally exceed a value greater than the limits fornormal use recommended by the manufacturer. An

    exception may be made for this when solarirradiation is too low to allow normal exposures tobe made and the development times for the filmneed to be increased. The client must always beadvised when this is likely to occur.

    Under certain lighting conditions an extendeddevelopment time may be required to provide aneffective increase in film speed. This will generate ahigher base fog density.

    4.3.7 Measurement of spatial resolution

    The spatial resolution in an original image is anindication of the resolving power which thephotographic system can achieve under practicalconditions. It is expressed as the average GroundSampled Distance (GSD), which is the product ofthe photo scale of the image and a measured valueknown as the Image Spread Function (ISF),representing the smallest discernible object.

    For this contract the average GSD for an image:

    either (a) is not requiredor (b) shall be measured for each film/

    camera combination used on thecontract.

    *Select the option required.

    Option (b) would-normally be selected only whenthe client is fully aware of the technical uses of theISF. Features selected for measurement of the ISFshould be chosen from as many areas of an originalimage as possible, with three or four images beingselected at random from the processed films. Notless than twelve linear or point response featureshaving a cross section close to the smallestdiscernible blur spot (otherwise known as the discof least confusion) would normally be selected ineach image and their widths measured.

    The coefficient of variation (CoV) in each set ofmeasurements made should normally not exceed30 per cent, where CoV=100 x (standard deviation/mean).

    The value of the ISF is the arithmetic mean of theset of measurements and is expressed inmicrometres.

    The GSD is calculated by the formula GSD=ISF xphoto scale, stated in metres.

    The microscope used for measuring the ISF shouldbe of a standard comparable to a good quality

    30 | VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY

  • instrument having a magnification range of betweenx40 and xlOQ and have a reticule calibrated insteps of not greater than 10 micrometres.

    4.3.8 Fiducial marks and marginal sata

    All fiducial marks shall be clearly visible and sharpon every frame. Digital data and camerainstruments recorded on the film shall be clearlylegible on all processed negatives. Failure ofinstrument illumination during a single sortie shallnot be cause for rejection of the photography.

    The fiducial marks are essential for the accurateproduction of information from the film. Theancillary information recorded on each exposureprovides additional quality control. Failure of thecamera illumination which imprints this data cannotbe rectified during flight and would result inexposures from that occasion not carrying theancillary information. A single failure would not be acause for rejection of the photography but furtherflights should not be undertaken until theillumination has been replaced.

    4.4 Photographic film products

    The principal photographic products produced fromfilm aerial photography are contact prints anddiapositives. Digital orthophotography and mosaicsare included in section 6.

    The principal analogue photographic product is theset of diapositives made from the original images.Contact prints should be supplied for normal day-to-day inspection. Mosaics may be created fromdigital imagery as an accompaniment to the data,either directly from digital data or from digital dataobtained from scanning film. Consideration needsto be paid to the resolution of, and use of digitalproducts as clients may only want a set of lowresolution images. Section 6 provides more userguide information, including file format and deliverymedia considerations. It is important that these arecorrectly specified if the delivered data is to bemanageable.

    4.4.1 Contact prints

    Contact prints shall be made on an automaticdodging printer on medium weight resin- coatedpaper or double weight fibre-based paper, on whichink can be used on both sides. The prints shall beboxed and sets shall be supplied

    The contractor shall agree with the client anyspecific requirements for details of trimming for theprints, use of title strip and the surface finish for theprint.

    *State number of sets required.

    The image quality of contact prints should providegood tone reproduction showing detail in lighttoned areas and, as far as possible, in areas ofshadow or dark terrain. The selection of the surfacefinish will affect the visual sharpness of the image.

    4.4.2 Diapositives

    Diapositives will normally be produced using adodging printer. Care should be exercised to ensureclose contact between the original image and thediapositive material.

    The diapositives shall be produced on:

    either (a) stable based filmor (b) glass plate.

    *Select the option required. Glass plates are onlyrequired under exceptional circumstances.

    4.4.3 Storage of diapositives

    Diapositives produced from the processed film shallbe stored:

    either (a) in boxes containing a number ofdiapositives

    or (b) in individual sleeves.

    4.5 Reports

    The format and method of delivery of reports by thecontractor should be agreed in advance by theclient. Contractors may be required to include theirproposals for delivery, frequency, contents andlayout of reports either in their tender submission orbe included in a Quality Plan approved by theclient.

    The following reports are required during the courseof the contract.

    4.5.1 Film reports

    The film report provides a technical summary ofeach sortie and should contain Date; AircraftRegistration; Camera/Sensor type and serial

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 31

  • number; Lens (focal length); Weather and flyingconditions; Exposure settings; Flying height; SortieNumber/flight runs as taken; Film Number/datastorage device number as appropriate

    The film report provides valuable archiveinformation which will be of benefit should theimages be used at a future date for other purposes.

    Two copies of each film report shall be supplied.One copy shall be retained in the film container,and one copy shall be delivered in the ProjectReport Folder. Each report shall contain thefollowing information:

    + name of client

    + name and address of contractor

    + film number

    + camera manufacturer, type, serial number, lenstype, number and focal length

    + filter type and number

    + film type and manufacturer’s emulsion number

    + lens aperture and shutter speed

    + run number and flight direction

    + dates of photography (years, months and days)

    + aircraft type and identification

    + names of pilots, navigators and photographers

    + start and end time for each run in local time

    + photo numbers of all offered photography

    + camera station coordinates

    + computed altitude above mean sea level

    + nominal scale of photography

    + weather conditions – cloud type, degree ofhaze and turbulence, etc.

    + date of processing

    + method of development

    + developer used and dilution

    + time and temperature of development and filmtransport speed

    + length of film processed

    + record of the sensitometric analysis results

    + ground sampled distance

    + general comment on quality.

    4.5.2 Progress reports

    The contractor shall submit a brief progress reportat agreed intervals on the flying of the photographyand of production of the derivative products.

    The client may request, or expect, reports atsignificant milestones such as being informed of:

    + the commencement of flying

    + the completion of acquisition of photography

    + the quality acceptance of photography

    + the commencement/completion of productionof derivative products.

    4.5.3 Project report

    A project report shall be delivered by the contractorupon completion of the project. The project reportshall contain the following information:

    + a brief project report recording planned andactual delivery dates, any problemsencountered and any changes or variations tothe original contract requirement

    + one set of folded paper copies of the indexplots

    + one set of film reports

    + one set of camera calibration certificates

    + a copy of the contract technical specification

    + metadata

    + a certificate confirming that the photographyhas been validated by the contractor andconforms to the specification.

    4.5.4 Navigation/positioning data

    GNSS data and associated observations from aninertial measurement unit data base station data.

    GNSS data and associated observations from aninertial measurement unit data is now normallycollected as standard practice and should besupplied as a matter of course at no extra charge.It is important that third party base (reference)station data is requested and ordered fromsuppliers and, where appropriate, national mappingorganisations promptly as such data may not bearchived in the precision required.

    4.6 Storage and preservation

    This specification introduces specific clausesrelating to the ownership, storage, copyright andmarketing of the films, in line with copyrightlegislation. Where appropriate, this will allow thecontractor to generate an income from sales, tocontribute towards the long term storage and

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  • preservation of the archive. Individual agreementsmay be made between the client and thecontractor, e.g. long term free storage of filmswhich may be reproduced with the permission ofthe client.

    See also 1.1.9, Ownership and copyright.

    While photographic materials remain in the care ofthe contractor they shall be stored in containers atall times.

    Film containers shall be stored in a secure andclean film vault with reasonable protection againstforeseeable causes of damage. The client shallhave the right to inspect the storage facilities at anytime during the contract while films remain in thecare of the contractor.

    All photography represents an historical record.Specialist care is required to conserve the materialin a good condition. When the client does not wishto retain the contract material, consideration couldbe given to offering the material to an appropriatenational, international or commercial archive. Onlyin exceptional circumstances should disposal of thefilm be contemplated.

    4.6.1 Archival quality of original films

    The original film represents a record which may beirreplaceable. It should be processed forpermanence. Specialist information is availableregarding the care of material for which absolutepermanence is required.

    Film is less likely to be damaged during handling ifit is kept in a roll and inspected only through anappropriate viewer. Note: to avoid handling/splicing

    of film, some clients may request that a dedicatedfilm is used for their project and that the remainingfilm left should not be used for any other client’sproject.

    The original films are required to be of archivalquality and shall be processed, washed and driedaccording to the film manufacturer’s instructions tominimise the residual thiosulphate content and anyother chemicals which would reduce the long-termstorage properties of the film.

    Each processed film shall be kept in roll form on aspool and in a metal or plastic container. Rejectedframes shall not be removed from the roll.Individual frames may not be cut from the roll forscanning or enlargement without the writtenconsent of the client.

    4.6.2 Annotation of photographic material

    All photographic material should be clearly labelledto protect against accidental separation of theproduct from the storage container. A standardisedsystem makes for easy indexing.

    During the contract and prior to the client takingpossession of the photographic product thecontractor is responsible for the safe storage of allfilms and other material.

    The information in the following table shall beannotated permanently on the film leaders, filmcontainers and on each image and contact print,where ticked in the table below. Standard stripsmay be provided with each film for titling contactprints, instead of numbering each imageindividually.

    Data Start and end ofeach film

    Film containerlabels

    Images andprints

    Start or end U U

    Name of client U U U

    Name of contractor U U U

    Contract area or project number U U U

    Camera manufacturer and type U U

    Film number U U U

    Run number U U

    Exposure numbers U U

    Dates of photography (yy,mm,dd) U U U

    Nominal photo scale U U U

    Flying height above mean ground level U U U

    Calibrated focal length of lens unit U

    VERTICAL AERIAL PHOTOGRAPHY AND DIGITAL IMAGERY | 33

  • 4.6.3 Insurance for Storage of Film andDigital Imagery

    It should be noted that where photography relatesto a specific event or moment in time thereplacement of the original image is impossible. Insuch cases the client should consider if anarrangement is necessary to hold duplicate materialat a separate location. Normal insurance coversonly the replacement costs of the material.

    Where the contractor has the responsibility ofstoring material on behalf of the client insurancecover will be required, appropriate to the expectedincome to be derived from the material. Theagreement may include full or partial payment ofthe cover by the client.

    The liability of the contractor for loss of or damageto the films, digital imagery and other documentsshall in no circumstances exceed the following:

    + where films/images are less than 12 monthsold, the replacement cost of new unexposedfilms.

    + where films/images are more than 12 monthsold, an amount equal to one years loss ofroyalty income, subject to the terms of a pre-existing marketing agreement.

    4.7 Scanning of film to obtain ‘derived’digital imagery

    The user guide notes for this section provideguidance for:

    + scanning of film to provide derived digitalimagery which can either be used in digitalphotogrammetric ‘plotting’ equipment toproduce mapping, or be used to create digitalimagery products

    + processing of imagery captured by digitalcamera and sensor systems

    + quality requirements for digital imagery

    + digital imagery products.

    The contract or specification may provide a choicebetween the use of film cameras or digital cameras,so either sections 1 or 2 will apply to the contract.Section 3 applies to the quality of all imagery eitherderived or directly captured.

    If the user finds it difficult to decide which optionsshould be taken then professional advice should besought. Consideration of the long term possibleusage of the data should be borne in mind whenseeking such advice.

    The photography shall be scanned to produceraster imagery suitable for display and manipulationin computer systems including geographicinformation systems (GIS). Clause 1 indicates theintended use of digital imagery from this project.

    All scanning shall be carried out to comply with thetechnical specification and the productspecification.

    4.7.1 Scan type

    The original photog