Hello, I have 2 locations, one with a lambert projection with a 1 km grid (comes from hydro1k), covering africa, and the other with a longitude latitude projection with a 0.5 decimal degrees grid (covering the world). I have a raster map on the lambert location that has values of 1 for a given area and 0 (or null) otherwise (corresponds with upstream basins) and I would like to compute the corresponding area covered on the lonlat grid. This would lead to a value for each cell in the lonlat grid corresponding with the fraction of the grid cell covered by 1 in the lambert map. So, for example, if the cell is completly in the area in the lambert map, the value in the lonlat map should be 1, and if half of the area of the cell from the lonlat map is covered by ones in the lambert map, the value in the lonlat map should be 0.5.
If the two maps were in the same location, I could set the region to be the one of the lonlat map, and do r.resamp.stats -w input=lambert_map output=fraction_covered But r.resamp.stats doesn't work with maps from different locations. And it seems to me that r.proj forgets the information about the initial grid although in this case it should be kept. I have read the manual pages and the wiki but couldn't find anything answering my question, except that it seems to be something uneasy to do in grass, since operations on different locations cannot be done in order to avoid losses of accuracy: http://grass.osgeo.org/wiki/Location_and_Mapsets I may be wrong, but it seems to me that this kind of use of ratios to interpolate from a grid to another would be something that is done regularly, and I guess that other kind of computations requiring that geographic informations are not lost for each map would also be useful. -- Pat _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user