On Fri, Nov 23, 2012 at 5:35 PM, Aren Cambre <a...@arencambre.com> wrote: > Thanks! > > I am not familiar with GRASS's release customs. Will this become part of a > binary release soon, or should I just pull down the latest release in the > 6.4.2 trunk? I'm assuming this has been merged into the trunk...
It should be available as a binary for Windows by tomorrow in the nightly builds [0]. Markus M [0] http://wingrass.fsv.cvut.cz/grass64/ > > Aren > > > On Fri, Nov 23, 2012 at 7:32 AM, Markus Metz <markus.metz.gisw...@gmail.com> > wrote: >> >> On Fri, Nov 23, 2012 at 2:07 PM, Aren Cambre <a...@arencambre.com> wrote: >> > Isn't taking about 10,000% too much time considered a bug? :-) >> >> Hmm, yes. v.kernel is fixed in devbr6 and relbr6 with r53982 and >> r53983, respectively. >> >> Markus M >> >> > >> > On Nov 23, 2012 5:11 AM, "Markus Metz" <markus.metz.gisw...@gmail.com> >> > wrote: >> >> >> >> On Fri, Nov 23, 2012 at 4:14 AM, Aren Cambre <a...@arencambre.com> >> >> wrote: >> >> > I'm able to reproduce reliably here. I'll email you details >> >> > privately. >> >> >> >> Thanks. I can confirm that v.kernel takes a long time in GRASS 6 with >> >> the settings provided by you. It does not crash, however. >> >> >> >> I can speed up v.kernel in GRASS 6 to complete in 10 minutes instead >> >> of 16+ hours, but I am not sure if this fix can/will go into GRASS 6.4 >> >> because by now only bugs should be fixed. >> >> >> >> Markus M >> >> >> >> > >> >> > Aren >> >> > >> >> > >> >> > On Thu, Nov 22, 2012 at 9:02 AM, Markus Metz >> >> > <markus.metz.gisw...@gmail.com> >> >> > wrote: >> >> >> >> >> >> On Sat, Nov 17, 2012 at 4:06 PM, Aren Cambre <a...@arencambre.com> >> >> >> wrote: >> >> >> > I have a dataset of just over 700,000 incidents that happened in >> >> >> > square-ish >> >> >> > Texas county that's about 30 miles on each side. >> >> >> > >> >> >> > Here's the parameters reported by v.kernel as it's executing: >> >> >> > >> >> >> > STDDEV: 1000.000000 >> >> >> > RES: 111.419043 ROWS: 458 COLS: 447 >> >> >> > >> >> >> > Writing output raster map using smooth parameter=1000.000000. >> >> >> > >> >> >> > Normalising factor=6482635.018778. >> >> >> > >> >> >> > >> >> >> > I am running this on a Windows 7 x64 machine with 8 GB RAM and an >> >> >> > Intel >> >> >> > Core >> >> >> > i7 Q720 1.6 GHz with 4 physical cores. I notice that it's not >> >> >> > multithreaded, >> >> >> > only using 1 core. >> >> >> > >> >> >> > It takes about 16 hours to complete. Is this correct? I'd like to >> >> >> > use >> >> >> > this >> >> >> > on a dataset with closer to 5 million records, and I'm really >> >> >> > concerned >> >> >> > how >> >> >> > long it may take. >> >> >> >> >> >> The time required by v.kernel is a function of the number of cells >> >> >> and >> >> >> the input parameter stddeviation. The larger any of these values is, >> >> >> the more time v.kernel will need. Nevertheless, I think that the 16+ >> >> >> hours are not correct. I tested with a vector with 3 million points >> >> >> for a grid with 2700 rows and 1087 columns, magnitudes larger than >> >> >> the >> >> >> grid used by you. v.kernel completes in just over one minute. >> >> >> >> >> >> > >> >> >> > I posted my question about the 16+ hours at >> >> >> > >> >> >> > >> >> >> > >> >> >> > http://gis.stackexchange.com/questions/41058/how-do-i-compute-v-kernel-maps-in-less-than-16-hours/. >> >> >> > Bill Huber, who si apparently knowledgeable about kernel density >> >> >> > calculations in general, posted a response, and he felt like a >> >> >> > kernel >> >> >> > density map shouldn't take much time at all. But digging more >> >> >> > deeply, >> >> >> > turns >> >> >> > out he had come up with a kernel density calculation method over a >> >> >> > decade >> >> >> > ago using Fourier transforms. See >> >> >> > http://www.directionsmag.com/features/convolution/129753 and the >> >> >> > next >> >> >> > two >> >> >> > articles linked to it (they are short articles). Apparently this >> >> >> > transforms >> >> >> > it from an O(n^2) problem to an O(n ln n) complexity problem. >> >> >> >> >> >> The approach of Bill Huber is raster-based, not vector based, making >> >> >> some things easier, at the cost of precision. The coordinate >> >> >> precision, however, is only needed for kernel functions other than >> >> >> uniform. In GRASS, you could get something like a raster-based >> >> >> density >> >> >> map by >> >> >> >> >> >> - exporting the points with v.out.ascii >> >> >> - re-importing the points with r.in.xyz method=n to get the number >> >> >> of >> >> >> points per cell >> >> >> - running a neighborhood analysis using a circular window with >> >> >> r.neighbors method=sum -c >> >> >> >> >> >> Optionally you could use the gauss option of r.neighbors to get an >> >> >> equivalent to v.kernel kernel=gaussian >> >> >> >> >> >> HTH, >> >> >> >> >> >> Markus M >> >> >> >> >> >> > >> >> >> > I inspected v.kernel's main.c >> >> >> > >> >> >> > >> >> >> > >> >> >> > (http://trac.osgeo.org/grass/browser/grass/trunk/vector/v.kernel/main.c), >> >> >> > and looks like v.kernel uses an output-centric method (using >> >> >> > Bill's >> >> >> > wording) >> >> >> > of calculating the output, which seems like O(n^2) complexity. >> >> >> > >> >> >> > So I guess what I'm getting at is it appears to me that the >> >> >> > algorithm >> >> >> > behind >> >> >> > GRASS GIS's v.kernel is straightforward but is a greedy algorithm >> >> >> > (http://en.wikipedia.org/wiki/Greedy_algorithm), which is fine, >> >> >> > but >> >> >> > it >> >> >> > make >> >> >> > take a while to execute. Is this true? >> >> >> > >> >> >> > Is there not spatial indexing I could add to the dataset? I've >> >> >> > done >> >> >> > various >> >> >> > Google searches on that and can't come up with anything clear. >> >> >> > >> >> >> > Aren >> >> >> > >> >> >> > _______________________________________________ >> >> >> > grass-user mailing list >> >> >> > grass-user@lists.osgeo.org >> >> >> > http://lists.osgeo.org/mailman/listinfo/grass-user >> >> >> > >> >> > >> >> > > > _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
