#807: r.watershed doesnt consider longer distance to diagonal neighbouring pixels ---------------------+------------------------------------------------------ Reporter: aread | Owner: [email protected] Type: defect | Status: new Priority: major | Milestone: 6.4.0 Component: Raster | Version: 6.4.0 RCs Resolution: | Keywords: r.watershed Platform: All | Cpu: All ---------------------+------------------------------------------------------ Comment (by helena):
Markus was right - the difference was due to handling elevations as int versus fp, so now I got the version with the diagonal fix and here is the comparison of spatial patterns grass64RC05 - SFD with integer elevation range ~ -200000 - +200000 note zig-zag main streams, missing flow accumulation along the road on the west ridge http://skagit.meas.ncsu.edu/~helena/grasswork/accum5K_gr64rc5_3d.jpg http://skagit.meas.ncsu.edu/~helena/grasswork/accum5K_gr64rc5.png grass65 compiled in Sep 2009, SFD with FP before diagonal fix range ~ -200000 - +55000 (why so much lower than grass64?) no zig-zag on main streams, more realistic pattern on streams, lots of diagonals on hillslopes http://skagit.meas.ncsu.edu/~helena/grasswork/accum5K_gr65_sep09.jpg http://skagit.meas.ncsu.edu/~helena/grasswork/accum_5Ksep09.jpg grass65 compiled Feb 2010, SFD with fp after diagonal fix range only slightly different, quite different pattern on hillslopes - note particularly NW section of the watershed where the previously diagonal flow changed to horizontal http://skagit.meas.ncsu.edu/~helena/grasswork/accum5K_gr65_feb10c_i.jpg http://skagit.meas.ncsu.edu/~helena/grasswork/accum_5Kdiag2010.jpg I can see that somebody might have liked the diagonal biased version better than the correct one. grass65 MFD - no difference between sep 2009 and feb 2010 range ~ -200000 - +16000 (lower than SFD as it should be, but still why such a diff between 64 and 65?) most realistic overall http://skagit.meas.ncsu.edu/~helena/grasswork/accum5K_gr65_mfd.jpg http://skagit.meas.ncsu.edu/~helena/grasswork/accum_5Kmfdi.jpg Compared to r.watershed in GRASS65, the GRASS64 results look really bad for this high resolution data - I assume for lower resolution data the difference won't be as stark but still grass64 will be much worse than the grass65 version. Should grass65 version of r.watershed be backported to grass64? although the difference in values needs to be explained (it may be mistake on my side) and Markus M may have some additional issues that need to be addressed, what do others think? who makes the decision? Helena -- Ticket URL: <https://trac.osgeo.org/grass/ticket/807#comment:9> GRASS GIS <http://grass.osgeo.org>
_______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
