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.
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"
Hi Chuck - it is great to see you involved again. Thanks for looking at
the color problem - it was a long standing issue that you were the best person
to resolve. We use r.watershed a lot with lidar and SRTM data and it works
very well.
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)
r.terraflow is not designed to output basins the way r.watershed does.
there is another code that I hope will be eventually contributed that takes
terraflow output and creates a map of watershed hierarchy.
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.
length-slope, slope-steepness maps show a lot of cross-hatching
artifacts. (dem is r.contour output; slope, pcurv, tcurv look alright)
I am not sure what you mean here, but I think that is because of the D8
algorithm. For LS factor that should be computed only for hillslopes
(becuase that is what USLE/RUSLE is for)
r.flow works better with Dinf method.
But for stream networks it is hard to beat r.watershed.
(Chuck you should write a full paper about it - I get
lot of questions about the algorithm and where it is published that I cannot answer,
the proceedings paper does not give too much detail.
If you would like some good applications, I have plenty.)
Helena
with such a long processing time the iterative process of picking the
correct threshold size requires a bit of planning.
> 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.
Did you read the manual?
not well enough apparently now I have & understand what it means
now I have & understand what it means