Following a thread I've opened on the grass-users list, I would like to suggest a proposal to add a flag, to the r.mapcalc command, to discrd  NULL values when evaluating aggregation functions like max(), min(), mode(), etc.

Looking into the code of, for example., the max() function [1], it seems that if a NULL value is in the set of the arguments, the result is set to NULL (if I understand it correctly).

With the proposed flag, I would like to ask r.mapcalc to do not consider the NULLs, and to the calculations only on the not-NULL subset of values.

This would let us do filtering (with row/columns offsets) as it is done in r.neighbors, where the NULL values are directly discarded.

giovanni

[1] http://trac.osgeo.org/grass/browser/grass/trunk/raster/r.mapcalc/xmax.c

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