A correction: as you can see from the stats, the differences are not only (1,-1,7) as I was saying... Now I have to check how much these differences affect the results. Anyway, above 99.5 % of values are equal.
2008/7/29 G. Allegri <[EMAIL PROTECTED]>: > Ivan anticipated me for a bit. > GREAT Markus! I could crunch Sardinia in one shot. I haven't measured > the time but it was less then 2 minutes, while with r.watershed I got > stalled. > Analyzing the differences between the r.watershed and r.watershed.fast > for a narrower region, there was some subtle, sparse differences > (1,-1,7) meaning 45° differences: > > The following are the differences values (from r.mapcalc) statistics > (number of pixels for values) > > -7 76 > -6 34 > -5 30 > -4 49 > -3 43 > -2 194 > -1 1165 > 0 813894 > 1 1218 > 2 253 > 3 83 > 4 45 > 5 25 > 6 93 > 7 250 > 8 22 > 9 21 > 10 5 > 11 15 > 12 30 > 13 18 > 14 3 > 15 5 > 16 4 > * 36917172 > > 2008/7/29 ivan marchesini <[EMAIL PROTECTED]>: >> First results of one test I did: excellent!!! >> >> 1392776 cells dem with steep slopes but also plain areas >> >> r.watershed.fast: 7 seconds >> r.watershed: 4 min and 14 seconds >> >> no difference at all between the two generated network paths... >> >> markus: many thanks.. >> >> >> Ivan >> >> >> Il giorno lun, 28/07/2008 alle 23.14 +0200, Markus Metz ha scritto: >>> Hello list, >>> >>> I'm not sure if this list is the right place or rather the developer list. >>> For the A * Search algorithm in r.watershed (memory version without -m >>> flag set, r.watershed.ram), I implemented a binary min-heap instead of a >>> linear array to store points in ascending order relative to elevation. >>> This improves the speed of <SECTION 2: A * Search> considerably, the >>> larger the map, the larger the speed improvement. A region with about >>> 1,800,000 cells is processed about 37 times faster than with the >>> original routine. A region with about 11,000,000 cells is processed >>> about 170 times faster than with the original routine (46.7sec vs. >>> 2h12m9sec on my system). <SECTION 4: Watershed Determination> takes now >>> the longest. >>> >>> Several tests (different region sizes, different DEMs) showed that the >>> results of the binary heap version are very similar but not 100% >>> identical to the original r.watershed, because of a slightly different >>> treatment of cells with equal elevation in a binary min-heap compared to >>> a linear array. Differences are found in difficult areas (equal >>> elevation of several neighbouring cells) where there are several >>> possible solutions for how water could flow. Still, compared with other >>> hydrology analysis methods, e.g. r.terraflow, the results can be >>> regarded as identical. >>> >>> The original code was only altered where necessary, only the sorting >>> method is new, everything else is unchanged. >>> Memory usage increases a bit, because a binary heap needs its own index >>> for each analysed point (in addition to the other indices already needed >>> by r.watershed.ram). >>> >>> My question is if there is interest in this faster version of >>> r.watershed and if someone wants to test it. >>> The source code is available on http://markus.metz.giswork.googlepages.com/ >>> >>> Regards, >>> >>> Markus >>> >>> _______________________________________________ >>> grass-user mailing list >>> [email protected] >>> http://lists.osgeo.org/mailman/listinfo/grass-user >>> >> -- >> Ti prego di cercare di non inviarmi files .dwg, .doc, .xls, .ppt. >> Preferisco formati liberi. >> Please try to avoid to send me .dwg, .doc, .xls, .ppt files. >> I prefer free formats. >> http://it.wikipedia.org/wiki/Formato_aperto >> http://en.wikipedia.org/wiki/Open_format >> >> Ivan Marchesini >> Department of Civil and Environmental Engineering >> University of Perugia >> Via G. Duranti 93/a >> 06125 >> Perugia (Italy) >> Socio fondatore GFOSS "Geospatial Free and Open Source Software" >> http://www.gfoss.it >> e-mail: [EMAIL PROTECTED] >> [EMAIL PROTECTED] >> tel: +39(0)755853760 >> fax (university): +39(0)755853756 >> fax (home): +39(0)5782830887 >> jabber: [EMAIL PROTECTED] >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
