Hi Paolo, On Tuesday 09 Jul 2013 13:21:41 Paolo Ruzza wrote: > Dear GRASS users, > > I am confronted with a "non-standard" problem and I would appreciate any > help that you can give me. I have several vector files (polygons) and an > arbitrary raster grid, only with category numbers associated to it. I would > like to overlay the vectors onto the raster grid in order to query it and > extract the categories of the raster grid which overlap with the polygons > of each vector file. I am not interested in getting any info from the > vector polygons, I just want know where the vector and the raster overlap. > I have already thought of a way of doing this-I guess it would naturally > come to mind of every GRASS user. This would involve converting the vectors > into a rasters and then query the raster grid and the rasterized vectors > with r.stats. This would be very easy to do, but my vectors have very > small islands, which can, of course, be converted into raster cells, if I > set them my region to a very fine resolution for. However, if I went down > this route, this would: i) massively slow down vector to raster conversion > ii) massively slow down the r.stats querying process. Just to give you an > idea of the magnitude of my problem I am using several vector layers > (hundreds) at global level and a raster grid at a 2 arc-minutes resolution. > I am kind of stuck and I am not sure if there is any computationally > efficient strategy to do what I want. Any help would be greatly appreciated!
I'm not sure that I have understood your problem... but maybe you can transform the raster into a vector and then check which polygons of your vector maps are contained/overlapped in the raster area... All the best. Pietro _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
