Lecture 3 spatial data modeling and management. 2015年11月19日 2015年11月19日 2015年11月19日 2 Spatial data structure Comparison of vector and raster Introduction

Lecture 3 spatial data modeling and management

2023年4月21日星期五 2

Spatial data structureComparison of vector and rasterIntroduction to spatial databaseData models in traditional databaseData base for GIS

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What is a data model ？

The heart of any GIS is data model A data model is a set of constructions for

describing and representing selected aspects of the real world in a computer

There is no single type of GIS data model that is best for all circumstances


The role of a data model in GIS


GIS data models

CAD 、 geographical and image GIS data model

Raster Data Model Vector Data Model Object Data Model



The CAD data model

A CAD model focuses on feature drawing only ,so that it does not represent any kind of relationships between objects


Image data model


Difference between image data model and raster data model

Image data do not have attribute table attached,so that they have only one attribute field.

Raster data have attribute table that can be joint to other tables ,so that they can have multiple attribute field.

application ： image data---image processing

raster data---spatial analysis and modeling

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Vector data model Vector data model uses a set of

coordinate and relationship to represent real world objects 。

Geometry objects:Point:single pointLine ： stringArea ： closed loop

other vector model:Triangulated Irregular Network:surfaceRegionDynamic segmentation:network

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Vector data model ：acquisitionSurveying instruments(total

station 、 GPS 、 level,etc.)Digitize mapIndirect methods:

Rater to vectorData from spatial analysis

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Vector data model ： how to describe

Storage and management of vector dataAssociate geometry data and attribute dataRelationship of spatial objects

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Vector data model—the spaghetti structure

Only to record position and attribute information of the spatial object,but not topological relationship

Storage ： Independence ： spatial objects with its geometry

information Point dictionary ： coordinate storage is separated from its

spatial objects Characters:

no topological relationship ,so that only can be used to presentation and simple query of spatial object

Exists data redundancy Can not keep consistency of the data,for the common part repeats

storage Spatial analysis is more complicated Can not deal with the operation of polygon

Appropriate applications ： For the disadvantages that stated above,this data structure can be

used to map and general query,but not for spatial analysis

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ID Attribute

Encoding of spatial objects Sole Associate the attribute and position

database Encodingpoint: ( x ,y )line: ( x1 , y1 ) , (x2 , y2 ) , … , ( xn , yn )area: ( x1 , y1 ) , (x2 , y2 ) , … , ( x1 , y1 )

Point dictionary

point

line

area

No X Y

1 11 22

2 33 44

… … …

n 55 66

Geometry

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Vector data model:example of spaghetti structure

1

23

45

6

7A

B

polygon code coordinate

A t123 1 ， 2

3 ， 4

…

B t124 5 , 6

No. of point

coordinate

1

2

3

4

5

1 ， 2

3 ， 4

5 ， 6

7 ， 8

…

polygon code No. of point

A

B

T123

t124

1,2,3,4,7,6,1

1,6,7,4,5,1

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Vector data model:the topological structure

Not only expressed the position and attribute of objects,but also relationship between objects

Generally the topological relationship is conjunction

The conjunction can be expressed in full expression and part expression

Storage Directly storageSerial pointer

Topological relationship and data share Conditions of using topological relationship

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Vector data model : full expression

N1

B2

N2

N4

N3B3 B4

B1

A1 A2

A6

A5

A4

A3

A7 A8

N5

A8

B1 B2 B3 B4

A1 A2 A3 A4 A5 A6 A7

N1 N2 N3 N4 N5

M

Area

Arc

Node

Polygon-arc Polygon Arc

Arc-node Arc from

Arc-polygon Arc Left

Node-arc Nod e Arc

to

Right

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Vector data model:part expression

Using part table to describe topological relation

System9 ： polygon-arc 、 arc-node

DIME ： arc-node 、 arc-polygon

The topological relationship is all in the above

states in current GIS

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Topological structure ： how to describe in computer

pointerpolygon-arc 、 node-arc ： it is not convenient

directly storage for unequal length of record

Example:POLYVRT

TIGER

Directly storageArc/Info 、 GeoStar

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Topological structure:topological relationship and data share

To keep data consistent

Move node with topological relation

Move node with no topological relation

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Topological relations ： when to use topological structure

Application Map and general query can not use topological

structure Topological relation can be used to spatial analysis

Objects can be described with topological relation Polygon object ： polygon-arc 、 arc-polygon Network object ： node-arc 、 arc-node

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Vector data model ： attribute

Type

type ： what is the object?

explanation information ： different attribute with the same object

description

Encode

Attribute table

The item of attribute table depends on users

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pointID

ID

Encoding Coordinate related line

Precision Control-point

gradeGeodesic

organizationGeodesic

years

lineID

ID

Encoding Coordinate from 、 to 、 left 、 right

Material Grade Build time

Breadth Managementorganization

……

……

areaID

ID

Encoding No. of

boundaryBuild time

ownerBuilding

areaBuild

organizationstructure ……

Spatial objects

Encoding Name of

objectMap color

Type of geometry

Map sign encoding

Attribute

Type of object and attribute

Map graphic data to attribute data linkage

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Triangulated irregular network

X-Y Coordinates

node# coordinates

1

2

3

11

. . .

x1, y1

x2, y2

x3, y3

. . .

x11, y11

Z Coordinates

node# z_value

1

2

3

11

. . .

z1

. . .

z2

z3

z11

1

2

3

6

5

87

9

11

10

4

A

B

C

D

E

F

G

H

I

JK

LM

NEDGES

adjacent

A

B

C

D

E

F

G

H

I

J

K

L

M

N

B, K

A, C, L

B, D

C, E, L

D, F

E, G

F, H, M

G, I

H, J, N

I, K

A, J, N

B, D, M

G, L, N

I, K, M

NODES

node#

A

B

C

D

E

F

G

H

I

J

K

L

M

N

1, 6, 7

1, 7, 8

1, 2, 8

2, 8, 9

2, 3, 9

3, 4, 9

4, 9, 10

4, 5, 10

5, 10, 11

5, 6, 11

6, 7, 11

7, 8, 9

7, 9, 10

7, 10, 11

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Triangulated irregular network (cont.)

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Dynamic segmentation

Dynamic segmentation associates multiple sets of attributes to any portion of a linear feature

Elements of dynamic segmentation : Route--- A route is a linear feature on which attributes are defined Measure---Each route is associated with a measurement system

Events---Attributes associated with a route Advantage of dynamic segmentation

• Define linear feature within a line coverage• Work with data in route-measure format• Apply attributes in route-measure to any part of a route without

modifying underlying coordinate data Used to network analysis

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Vector data structure ： advantages and disadvantages

Distinct location and implicit attributeRepresent spatial relation with topological

relationshipsObject-based operation with high accuracy and less

data redundancyDifficult to combine with RS dataHigh quality graphics

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Definition Divides the entire study area into a regular grid of cells,each cell contains a single value

In rater data structurePoint ： pixel or cellLine ： represented in cluster of adjacent pixel 。Area ： pixel with same attribute that are congregated

Data sources ：Remote sense imageScanner Vector to raster Manual

Raster coordinates Compress raster data Raster layers Rater data file structures Advantage and disadvantage of raster data structure

Raster data structure:contents

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Point

Line Area

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Raster data structure ： coordinate system and parameters

Y ： Col

X ： Row

North-west coordinate

（ XWS ， YWS ）

Resolution

Grid direction

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Raster data structure ： assign value to cell

C

A

B

Percentage

Area

importance

Midpoint

A C A AB

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Raster data structure:compression

A AAAA RAAA RAAA RAA

R AAAA AAAA AGGA AGGG GGGG AGGG AGGA AAA

A ARAA AARA AARR AAA

1 432 5 87612345678

0

12

3

4

56

7Number of start row and column,unit vectorR: (1,5),3,2,2,3,3,2,3

Chain codes

Run-length codes Recording on row or columnNo. of row ,attribute, number of repeats1, A, 4, R, 1, A, 4

Block codes Rectangle Initial position, radius, value(1,1,3,A),(1,5,1,R),(1,6,2,A),¡

NE SWNW

SE

G

GGGAGGAAGAAA

Quarter-treecodes

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Hierarchy of the raster data structure

Soil

relief

Forest

Building Z

Y

X

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File structure of the raster data structure

Each cell is referenced directly , Map file

Point X coordinate

Y coordinate

Next overlayvalues

Overlay values

…

…

Next point

Each overlay is referenced directly, Map file

Overly Point

Next overlay

…

(X,Y) coordinate

Z value

Next point …

… …

…

Each mapping unit is referenced directly

Overlay tile

Next overlay

X,Y Coordinates pairs

Lable

Display symbol

Mapping unit 1

Attribute

Scale

Next mappingunit

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Raster data structure:advantages and disadvantages

Spatial object represented in discrete cell value

Location is implicit and attribute is distinctSimple data structure and easy to combine

with RS dataExisting errors in geometry and attributeDifficult to build the relationship between

spatial objects

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a b

c

3

4

5

a b

c

Ac distance: 7/4 (5)area: 7 (6)

Geometry bias

Attribute bias

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Com

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Vector model

advantages ：•It provides a more compact data structure than the raster model

•It provides efficient encoding of topology ,and as a result ,more efficient;implementation of operations that require topological information ,such as network analysis

•The vector model is better studies to supporting graphics that closely approximate hand-drawn maps

disadvantages ：•It is a more complex data structure than a simple raster

•Overlay operations are more difficult to implement

•The representation of high spatial variability is inefficient

•Manipulation and enhancement of digital images can not be efficiently done in the vector domain

Raster model

advantages ：• It is a simple data structure

• Overlay operation are easily and efficiently implemented

• High spatial variability is efficiently represented in a rater format

• The raster format is more or less required for efficient manipulation and enhancement of digital images

disadvantages ：• The raster data structure is less compact

• Topological relationships are more difficult to represent

• The output of graphic is less aesthetically pleasing because boundaries tend to have a blocky appearance rather than the smooth lines of hard-drawn maps.this can be overcome by using a very large numbers of cells ,but may result in unacceptable large files

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Object or fieldsAcceptable data Necessary accuracy of spatial objects location Topological relationshipsType of spatial analysisType of map

Principles of selecting data models

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Spatial data management ： spatial database data base

A data base is defined as structured collection of information on a defined subject

characters：Data is independent on application programsRelationship of data represent the connection of

information in the real worldConventional data base management structures

Hierarchy database structureNetwork database structureRelational database structure

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Spatial data management ： spatial database （ cont.）

Spatial database A spatial data base is a collection of geographical

data and information on a defined areacharacters：

Huge data quantity Location and attribute data combinedBroad application areas

Features of spatial data basespatialityNon-structuredSpatial relationshipsClassification encoding Huge data quantity

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Comparison of conventional database and spatial database

Conventional database

Spatial database

continuous/correlationDiscontinuous

Non-correlation

Continuous

Spatial correlation

Type of entity/spatial relationship

Few

Steady

Many

Unsteady

Record length Structured

Equal

Non-structured

Unequal

Query and manipulation

words 、 numbersSpatial operations besides words and numbers

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Spatial database management Hybrid model based on data file and

relational database Extended model based on relational

database Integrated model based on object-

relation database

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location

attributeID

data file

database

early

Graphic interface

Graphic process DBMS

Attribute interface

Graphic filedatabase

Attributedatabase

GIS interface



Attributedatabase

Developmentlanguage ODBC agreement

GIS interface



Attributedatabase

Developmentlanguage

Database developmentlanguage

Database

development

Database development

Spatial data management based on file-relational database

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GIS interfaceGIS interfaceAttribute data（ equal records ）

Attribute data（ equal records ） Spatial data

（ unequal records ）Spatial data

（ unequal records ）

DBMSDBMS

Spatial database

Spatial database

Relationaltables

Relationaltables

Binary blocks

Binary blocks

Spatial data management based on relational database

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GIS interface

Spatial data process

DBMS

Spatial database

Extend entities type

Spatial data management based on object-relation database

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GIS spatial data organization

Study domain GIS project

Concomitantcontrol

Spatial index Workspace 1

Workspace2

Workspace n

Work layer

objects

Logic layer

Arc/Info

MGEGeoStar

Attribute Arc/Info

MGEGeoStar

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Spatial data index

What is spatial data indexWhy is spatial data index needed in

GISHow to build spatial data index

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Spatial data index:object range index

ID Xmax Xmin Ymax Ymin

1 … … … …

2 … … … …

3 … … … …

… … … … …

4 YmaxYmin

Xmin

Xmax

Collection of spatial objects

1

23

45

6

Retrieved windows

XN

YW YE

XS

Xmax>=XN OR Xmin<=XS OR

Ymax>=YE OR Ymin<=YW

No

XE<=Xmax,Xmin<=XN ANDYW<=Ymax,Ymin<=YEYES

XN

YW YE

XS

23

6

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Spatial data index :index based on grid

P(3,3)=6P(3,1)=4 P(3,2)=10

3 41 2

P(2,3)=1P(2,1)=7 P(2,2)=8

3

1

4

2

Header pointer

ID P

1 0

2 0

3 0

4 0

5 2

6 0

7 3

3 41 2

3

1

4

23

75

2

104

8

9

1

6

8 5

9 0

10 9

Link pointer

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Lecture 3 spatial data modeling and management. 2015年11月19日 2015年11月19日 2015年11月19日 2 Spatial data structure Comparison of vector and raster Introduction