Markus Metz wrote:
r.watershed in 6.5+ can do MFD which reduces these single-cell strings
substantially. I would recommend MFD over SFD for anything with 30m
resolution or higher, not much gained for 90m or coarser. Results are
generally more accurate with MFD for high resolution (<= 30m) DEMs.
Markus M
I finally got around to compiling GRASS 6.5, with the r.watershed MFD
options, and I must say... wow!
First, the memory handling must be much better. I'm working on a region
with about 80 million cells. Theoretically I should need 2.5 GB to run
the module in memory. There are many null cells surrounding the actual
basin, but still, On my aging Pentium 4 with 1 GB memory, using the
older r.watershed (GRASS 6.4) I would run out of memory, and I'd have to
use the "seg" mode, which of course took hours and hours.
Now the newer module whips thru the same dataset in about 20 minutes.
And more importantly, using the -f flag (Multi flow direction) the
original problem of "ladders" or strings of single cells in the
catchment raster has almost disappeared!
The only remaining problem I noticed is streams that split and
reconnect. Although this was quite minor.
Best regards,
Micha
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