Shape analysis and measurement are very important to analyze the shape of area objects in GIS.
The following parameters are computed from vector data.
Area:
where xn+1 = x1, yn+1 + y1
Perimeter:
Centroid (Center of Gravity) (see Figure 4.11)
The above parameters of area and the centroid can be computed easily from raster data by simply summing the number of pixels of the polygon and averaging the x and y coordinates respectively.
The perimeters can be computed by counting the chain codes around the boundary of the polygon.
The following parameters indicating the shape of the polygon are also used widely in the shape analysis as shown in Figure 4.12.
Horizontal maximum chord: CHORD H
Vertical maximum chord: CHORD V
Horizontal Feret’s Diameter: FERE H
Vertical Feret’s Diameter: FERE V
Maximum Length: MAXLING
Breadth: BR’DTH
Orientation: q
The following shape factors are also used for shape analysis as shown in Figure 4.13.
Roundness Factor:
Unevenness:
Flatness: