Vector Data Modeels
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Transcript of 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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Triangulated irregular network
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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Triangulated irregular network
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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Triangulated irregular network
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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Triangulated irregular network
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.