[R] random location in polygons sp spsample splancs csr
Dear all, I had to place points at random, one in each of larger number of polygons (actually in objects of class 'SpatialPolygonsDataFrame' , see sp library), and tried first to do it using spsample (from sp). Surprisingly, every 5-15 trials, the output was a NULL value. The doc says that ' this may occur when trying to hit a small and awkwardly shaped polygon in a large bounding box with a small number of points', but in my case, the shapes were not really awkward, and the bounding box just the smallest rectangle including the shape, just the number of points was 1 in each polygon. Thus I tried csr (from splancs) after having extracted the polygon coordinates of each shape from the Spatial object, and everything went smoothly, with hit success every trial. Has anybody (anybody will probably be Edzer or/and Roger...) an idea why here splancs looks like outperforming spsample ? Patrick __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] random location in polygons sp spsample splancs csr
Thanks for those detailed explanation and the time taken to write them. The spsample methods for polygons have an iter= argument that can be used to make then try harder, did you try it (with what values - the help page senctence you quote is from the iter= description)? Yes sure, I went up to 10, but no success. Could you provide an example with a set.seed() value that does what you say, or at least the code you used? The easiest way is to send the data and the script off list. I will do it. Did you try asking for multiple points and then choosing a single point at random? This would be equivalent to increasing iter while asking for a single point. I did not try this one Actually, I found my way out easy with csr() in splancs, and did not fight too much with spsample. My question on the list was just for general information PS. Perhaps R-sig-geo is a more appropriate list? I was wondering too... and chose r-help because I though the question was of 'general' interest enough. This is debatable indeed... Thank you anyway for your answer, and see you in a few minutes off list... Cheers, Patrick __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
