Hi Jonathan, the process you described works for me in QGIS 1.8.
After fiddling with your dataset I reverted to a minimal example of a dozen polygons and three groups. After converting the singleparts to multiparts I asked for 5 "random points" in "stratified sampling design". Each multipart feature got 5 points and in every multipart the points where spread out across all polygons belonging to that multipart. So I guess its a matter of size. cheers robert Am Donnerstag, 5. September 2013, 16:09:53 schrieb Jonathan Greenberg: > QGISers: > > I'm trying to realize stratified random sampling using a > classification raster that I polygonized. It seems like the random > points tool will create random points within each polygon, but in my > case the strata are the classes, which can be scattered across a > landscape -- in other words, multiple polygons make up a single strata > (I'd argue this is a more valid definition of stratified random > sampling). I'd like to choose, say, 10 random points falling in each > group of polygons with a given shared (classification) attribute. Is > there any way to realize this in QGIS? I tried pre-converting the > polygonized classification file to a multi-part polygon, but the > random sampling tool froze up when I used this as an input. > > I dropped the polygon layer (derived from the classification raster) in: > https://drive.google.com/folderview?id=0B8Kij67bij_AMmNPakJmT1p4OWc&usp=shar > ing > > The "DN" attribute is the strata I want to use (notice multiple > polygons have the same DN). > > To be clear: I don't want 10 points per polygon, I want 10 points per "DN". > > Thanks! > > --jonathan _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
