Geography Reference
In-Depth Information
Figure 9.5 Shaded '2.5D' visualization of the TIN in Figure 9.4(C), viewed from the south east.
Based on a z conversion factor of 0.04.
53
x 4
29
x 2
x 0
48
68
x 3
x 1
Figure 9.6 Location of prediction location and observations. Values and ID codes are given
for the four samples and the value at location x 0 is treated as unknown.
For example, where the coordinates are given by x and y , the independent variables
may be, for example, just x and y (this is called a i rst-order polynomial trend) or x , y ,
xy , x 2 and y 2 (this is called a second-order polynomial trend). Such approaches are
useful for depicting general trends, but are unlikely to be of much practical use for
direct interpolation.
Inverse distance weighting
9.5
Weighted moving averaging is a widely used approach to interpolation. A variety of
dif erent weighing functions have been used but IDW is the most common form in GIS.
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