GMS:Subset Definition

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The Subset Definition dialog.

In the IDW Interpolation Options dialog, an option is available for using a subset of the data points (as opposed to all of the available data points) in the computation of the nodal function coefficients and in the computation of the interpolation weights. Using a subset of the data points drops distant points from consideration since they are unlikely to have a large influence on the nodal function or on the interpolation weights. In addition, using a subset can speed up the computations since less points are involved.

If the Use subset of points option is chosen, the Subsets button can be used to bring up the Subset Definition dialog. Two options are available for defining which points are included in the subset. In the first approach, only the nearest N points are used. In the second approach, only the nearest N points in each quadrant are used as illustrated in the figure below. The second approach may give better results if the data points tend to be clustered.

The four quadrants surrounding an interpolation point.

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