Re: [GRASS-user] Select random cells from map
Thanks Hamish I thought that random cells are retrieved from valid "map" cells. Or not? Antonio Hamish wrote: 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 __ Information from ESET NOD32 Antivirus, version of virus signature database 5177 (20100606) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __ Information from ESET NOD32 Antivirus, version of virus signature database 5178 (20100607) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Select random cells from map
> > 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 grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Select random cells from map
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? 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. good luck, Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Select random cells from map
Hi. I missed that r.random :) It seems to do what I need. I just need to understand a bit more what is the COVER parameter Thanks nikos Nikos Alexandris wrote: António Rocha: Hi there 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? Doesn't "r.random" (not "r.random.cells") work? I think it works on/for non- NULL cells. In case r.random.cells and its capabilities are required, couldn't you just create a non-NULL MASK and limit its operation as you wish? Nikos __ Information from ESET NOD32 Antivirus, version of virus signature database 5163 (20100601) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __ Information from ESET NOD32 Antivirus, version of virus signature database 5163 (20100601) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
