On Thu, 19 Apr 2012, Margherita Di Leo wrote:
Please post information about the region, r.info of the map and the command line of r.watershed that you use. Also, do you use a mask? Pankaj Kr Sharma, please avoid to reply attaching the whole digest.
madi, Micha, Pankaj: The Level 6 HUC basins (a.k.a. HUC-12 or sub-watersheds) are defined by the USGS to enclose areas of 10k-40k acres (15.625-62.5 square miles; 40.5-161.9 square kilometers). These are a bit too large, but vector boundaries for 14- or 16-digit hydrologic units are not available for this area (or for my other project area which is approximately 125 square miles, 323.75 square kilometers) so I tried different threshold values for r.watershed and 150000 seems to provide additional resolution without generating a separate drainage for each individual stream segment. Yes, it's arbitrary. But for the purposes of these two projects it is a practical balance between too coarse and too fine. The region was set by the base, 10m DEM: projection: 99 (Lambert Conformal Conic; units in International Feet) zone: 0 datum: nad83 ellipsoid: grs80 north: 735780 south: 655650 west: 2042100 east: 2138580 nsres: 30 ewres: 30 rows: 2671 cols: 3216 cells: 8589936 The r.watershed command line (all on one line but wrapped in the MUA): r.watershed -f elev=dem10m.avg acc=dem.acc drain=dem.drain bas=dem.basin stream=dem_str.seg thresh=150000 --o And r.info for dem.basin: Type of Map: raster Number of Categories: 94 Data Type: CELL Rows: 2671 Columns: 3216 Total Cells: 8589936 Projection: Lambert Conformal Conic N: 735780 S: 655650 Res: 30 E: 2138580 W: 2042100 Res: 30 Range of data: min = 2 max = 94 Data Source: dem10m.avg Data Description: generated by r.watershed Comments: Processing mode: MFD Memory mode: All in RAM r.watershed -f elevation="dem10m.avg" accumulation="dem.acc" drainag\ e="dem.drain" basin="dem.basin" stream="dem_str.seg" threshold=15000\ 0 convergence=5 memory=300 If the white areas with vector streams (the blue lines) represent basins, then that's OK. What puzzles me is why a couple of basins would be white while the others are different colors and the small white areas without mapped streams are appently external to the basins of interest. As far as I know, there's no attribute table for raster maps that hold descriptions of the generated basins, only information on the contents of each cell. Rich _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user