[GRASS-dev] r.watershed updates

Hamish hamish_nospam at yahoo.com
Sun Oct 29 04:22:54 EST 2006


Now the lots-of-colors bug is fixed, I've now run r.watershed on a large
grid (5000x5000 cells [20% null]). It took 54 hours, basin/half-basin
results look nice, especially with: "nviz elev=topo color=basins.half"

r.terraflow with the same area & mem=1500MB took just minutes, but only
outputs sink-watershed basins, not all basins. (I may be missing
something here, this is all outside my field)

some weirdness/comments:

Accumulation map: number of cells that drain through each cell
 |   Range of data:    min = -16269552  max = 8562412   

(way negative? way postive?) bulk of data is 0->2000 though, so after
setting color rules the map looks ok.

stream map: 0 -> null
basins,half-basins: 0 -> null

length-slope, slope-steepness maps show a lot of cross-hatching
artifacts. (dem is r.contour output; slope, pcurv, tcurv look alright)

with such a long processing time the iterative process of picking the
correct threshold size requires a bit of planning.

used ~ 570mb RAM (all-in-memory mode)


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