[GRASS-dev] r.watershed and swap memory

[Hamish]

Ivan wrote:
> We have this kind of problem:
> * a large DEM (150000000 cells)
> * an ordinary computer (2 GB ram)
> * we must obtain the drainage map using r.watershed (without
> changing resolution), because then we need to be able to calculate
> the upstream basin for each cell (r.water.outlet).
> * we have tried r.watershed straigth (but after few seconds a
> memory allocation problem crashed the program)

I am pretty sure that in the past I have run r.watershed for a
14000x12000 region on a machine with 2GB RAM (+2 swap) (I'd have to dig
out a backup cd to check exactly; I think that was without the -m flag).
It had to run that over a weekend but it did finish. Perhaps you are just
on a threshold of being too large? Can you crop the region slightly or
run with a slightly coarser resolution to see where the memory limit is?


Hamish



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