> > António wrote: > >> I need to randomly select non-null cells from a given map. > >> I tried r.random.cells but I cannot define a maximum number > >> random cells and some selected random cells are not valid > >> values in my map. is there any other function to randomly > >> select cells from a raster?
Hamish: > > r.to.vect to get a vector area coverage of your raster (do > > not use the -s flag), then v.random.cover from wiki addons > > then v.to.rast, and finally r.mapcalc to transfer values from > > source map to random cell map? (probably we/I should make a > > new wrapper script to do that automatically) > > > > or you might skip the last steps and just use v.random.cover's > > raster= option to sample the raster map directly. > > > > probably the best idea is to fix r.random's cover= option to > > loop until it has enough points. > > > > > > also if you will be doing a lot of geostats it is probably > > worth your while to learn about the GRASS<->R interface: > > http://grass.osgeo.org/wiki/R_statistics > > > > ... then the world is open to you. António wrote: > Thanks for your answer. I tried r.random with my input data and the > number of cells and it worked but I do have one question: I didn't > understand the objective of cover_map. I used the map from I want to > extract random cells as input but what is the objective of cover_map? r.random creates random points all over the current rectangular region block. Adding a cover map makes those random points only occur within the irregular area covered by the cover map. (but r.random cover= is a bit buggy right now; see new ticket in the bug trac'er) Hamish _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
