r.resamp.filter resamples an input raster, filtering the input with an analytic kernel.
All of the kernels specified by the filter= option are multiplied together. Typical usage will use either a single kernel or an infinite kernel along with a finite window.
Resampling modules (r.resample, r.resamp.stats, r.resamp.interp, r.resamp.rst, r.resamp.filter) resample the map to match the current region settings.
When using a kernel which can have negative values (sinc, Lanczos), the -n flag should be used. Otherwise, extreme values can arise due to the total weight being close (or even equal) to zero.
Kernels with infinite extent (Gauss, normal, sinc, Hann, Hamming, Blackman) must be used in conjunction with a finite windowing function (box, Bartlett, Hermite, Lanczos)
For longitude-latitude locations, 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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