r.resamp.interp fills a grid cell (raster) matrix with interpolated values generated from a set of input layer data points. A choice of three interpolation methods is available; each uses the weighted values of a different number of adjacent cells in the input map to determine the value of each cell in the output map as follows:
Note that for bilinear and bicubic interpolation, cells of the output raster that cannot be bounded by the appropriate number of input cell centers are set to null. This could occur due to the input cells being outside the current region, being NULL or MASKed.
For longitude-latitude databases, the interpolation algorithm is based on degree fractions, not on the absolute distances between cell centers. Any attempt to implement the latter would violate the integrity of the interpolation method.
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