[GRASS-user] Overlapping pixels among DEM tiles to compute the LS factor for RUSLE

[Ken Mankoff]

Hi Nikos,

On 2019-01-25 at 07:18 -0800, Nikos Alexandris <nik at nikosalexandris.net> wrote...
> A billion-pixel scaled DEM is the main input to compute the slope length
> and steepness (LS) factor for RUSLE (`r.watershed`), only.
>
> Tiling this DEM in tiles of 5K^2 pixels (`r.tile`), appears to be a
> reasonable approach to parallelise this process.

Do you need to parallelise it? I just ran r.watershed on a 4.5 billion-pixel DEM w/o a problem on my laptop and I think it took ~6 hours, but I'm not sure. It might have been closer to 12. I have 32 GB of ram and gave half to the process, but told it to use disk instead of memory via the -m flag:

r.watershed -s -m elevation=phi threshold=1000000 drainage=dir memory=16384 --v --o

  -k.