vector data modeels

7/29/2019 Vector Data Modeels

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VECTOR DATA MODEELS


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Vector data model

Provides precise position of features in space.

The approach used in this models is to precisely specify

the positions of points, lines, polygons , which

represents different features of interest. The main assumption in this model is that positions of

coordinates are mathematically exact .

The location of features on the earths surface are

referenced to map positions using an x,y coordinate

system termed as cartesian coordinate system.


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Classification of vector models

SPAGHETI MODELS

TOPOLOZICAL MODELSTIN MODELS


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SPAGHETI MODELS

The paper map is translated point by point, line for line

into a list of XY coordinates.

An area is represented by closed polygon of xy

coordinates that defines its boundaries. The common boundary between adjacent polygons

must be recorded twice i.e. once for each polygon.

A file of saptial data constructed in this manner Isessentially a collection of coordinate strings with no

inherent structurehence the term spagheti model


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SPAGHETI MODEL

The structure of this model is simple and easy to

understand.

The data model is really the map expressed in

Cartesian coordinates . Though all the spatial features are recorded but the

spatial relationship between features are not encoded.

The spagheti model is very inefficient for most types ofanaalyses since any spatial relation should be derived on

computation


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SPAGHETI MODELS

.35

X535 36

14

X536 14

ANALOG MAP

DIGF\ITALMAPIN CARTESIANCOORDINATES


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DATA STRUCTURE

FEATURES NUMBER LOCATION

POINT 5 X,Y

LINE 14 (X1,Y1),(X2,Y2),(X3,Y3), (X4,Y4)

POLYGON 35 CLOSED LOOP OF XYCOORDINATE PAIRS WHERE

FIRST AND LAST PAIRS ARE

SAME36 CLOSED LOOP SHARING

COORDINATES WITHADJACENT POLYGONS TOFORM A DATA STRUCTURE


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Topological model

This model is widely used method ofencoding spatial relationships in GIS.

Topology is the mathematicalmethod used to define spatialrelationship.

This particular form is also known asARC-Node data model.


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Topological model

The basic logical entry is the arc.

A series of points that end at a node.

A node is an intersection point of twoor more arcs meet.

A node also occurs at the end

dangling arc i.e. an arc that is notconected to another arc. Example isdead end of a street.


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Topological model

A polygon is a comprised of a closedchain of arcs that representsboundaries of an area.


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Topology Recording

1 EN1

N2

N3 N5

N6

a1

a2

a2

a2

a3

a3

a4

a4 N4

a5

26

a6

a6

a6

A

BCD

10 70

10

60


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Topology Recording

Topology is recorded in threetables one for each spatial

elements. Node topology

Arc topology Polygon topology


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SPATIAL ENCODING

ARC TOPOLOGY

Arc Startnode

Endnode

Leftpoly

Rightpoly

a1 N1 N2 E Aa2 N2 N3 E B

a3 N3 N1 E A

a4 N1 N4 A A

a5 N3 N2 A B

a6 N5 N5 B B

a7 N6 N6 B C


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SPATIAL ENCODING

POLYGON TOPOLOGY

POLYGONS ARCS

A a1,a5,a3B a5,a2,0,a6,0,a7

C a7

D a6

E Area out-side mapcoverage


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SPATIAL ENCODING

NODE TOPOLOGY

NODE ARCS

N1 a1,a4,a3

N2 a1,a2,a5

N3 a2,a5,a3

N4 a4N5 a6

N6 a7


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SPATIAL ENCODING

ARC COORDINATE DATA

ARC START INTERMEDIATE END

a1 40,60 70,60 70,50

a2 70,50 (70,10),(10,10) 10,25

a3 10,25 (10,60) 40,60

a4 40,60 (30,50) 40,50

a5 10,25 (20,28),(30,30),(35,50)

70,50

a6 30,20 30,20

a7 55,28 (55,15),(38,15),(45,25)

55,28


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Triangulated irregular network

The TIN model is a used to represent aterrain surface.

The terrain surface is represented by

using interconnected triangular facets. For each of the three vertices x,y,z

coordinates are encoded.

Each triangle or facet is designated by aletter and is defined by three nodesdesignated by numerals.


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NODE TABLE:

PROVIDES EACH TRIANGLE ANDTHREE NODES.

Edge Table:

It gives the information about thethree triangles adjacent each facet.

The triangles that face boundary providesonly two adjacent facets.


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Node coordinates:

The x,y coordinate table and z coordinatetable store the node coordinate values.

The triangulation in which triangles aremost equilateral in shape tend to mostaccurately represents surface.


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TIN helps in finding slope, aspect foreach facet and stored as theattributes of the facet.

This is similar to the attributes ofpolygons.


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EXAMPLE

7

1

2 3

4

8

9

5

6

10A

B

CD

E`

F

G

H

I

J

K


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X, Y CORDINATES

1 X1,Y1

2 X2,Y2

3 X3,Y3

Z COORDINATE

1 Z12 Z2

3 Z3

10 Z10

EDGES

ADJACENT

A J,B

B A,CC BD

K J,D,F

TIN MODEL

NODES

NODES

A 1,8,7

B 1,2,8

C 2,8,3


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COMPARISONS OF RASTER

AND VECTRO MODELS 1.It is a simple structure.

2. Overlay operations areeasily and efficientlyimplemented.

3.High spatial variabilityis efficiently representedin a raster format.

4. The raster format ismore or less required forefficient manipulationand enhancement ofdigital images.

1. It provides morecompact data structure.

2. It provides efficient

encoding of topology.

3. The vector model isbetter suited for

supporting graphics thatclosely approximate handdrawn maps.


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Disadvantages. 1. The raster data is less

compact.

2. Topologicalrelationships are moredifficult to represent.

3. The output of graphicsappearance is lessaesthetically pleasingbecause boundaries tend

to have blockyappearance instead ofsmooth lines on handdrawn maps.

1. The data structure ismore complex.

2. Overlay operations aredifficult to implement.

3. The representation ofhigh spatial variability isinefficient.

4.MANIPULATION ANDENHANCEMENT OFDIGITAL IMAGES CANNOT BE EFFECTIVELYDONE IN THE VECTORDOMAIN.

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