[GRASS-user] r.watershed / r.terraflow - huge area (amazon)

[Carlos Grohmann]

Hi,

Sorry for the bad math :)

I mixed up things. With 03-sec resolution, I have 1.4 billion cells, and
r.watershed would need 45.5 GB.
With 01-sec resolution, I have 12.8 billion cells and r.watershed need
about 415 GB.

The Location is in a drive with 1TB free. So this shouldn't be a problem.
I'm running it now and it seems it's going to work. I'll report on this
tomorrow.


I think I didn't expressed correctly the r,terraflow issue. I didn't meant
if the rows/columns limit is needed in the sense of it being a required
parameter, but it was more of a general question, in the sense of 'do we
need to have that limit hardcoded?' I can open a ticket on this issue.

best

Carlos



On Tue, Jan 10, 2017 at 2:51 PM, Markus Neteler <neteler at osgeo.org> wrote:

> On Tue, Jan 10, 2017 at 12:30 PM, Carlos Grohmann
> <carlos.grohmann at gmail.com> wrote:
> > Hello all
> >
> > I'm working on deriving a nice drainage network for the Amazon basin. The
> > problem is that the area is too large.
> >
> > The region settings are these:
> > projection: 3 (Latitude-Longitude)
> > zone:       0
> > datum:      wgs84
> > ellipsoid:  wgs84
> > north:      6:17N
> > south:      21:30S
> > west:       80:37W
> > east:       44:50W
> > nsres:      0:00:03
> > ewres:      0:00:03
> > rows:       33340
> > cols:       42940
> > cells:      1431619600
> >
> > With 14.3 billion cels,
>
> Isn't it 1431619600 = 1.431.619.600 = 1.4 billion cells?
>
> > r.watershed would need about 450 GiB of disk space
> > running in seg mode, is that correct? (from the manual, 31 MB for 1
> million
> > cells).
>
> https://grass.osgeo.org/grass72/manuals/r.watershed.
> html#large-regions-with-many-cells
> " The upper limit of the ram version is 2 billion (2^31 - 1) cells,
> whereas the upper limit for the seg version is 9 billion-billion (2^63
> - 1 = 9.223372e+18) cells."
>
> So that would be supported by r.watershed.
>
> > I do have that disk space available, but it's in a secondary drive. If I
> set
> > TMPDIR to that drive, will r/watershed use it? I ask because the
> > documentation (https://grass.osgeo.org/grass72/manuals/variables.html)
> only
> > says that this environmental variable is used by "[Various GRASS GIS
> > commands and wxGUI]".
>
> AFAIK the TMPDIR variable is not relevant here. The tmp dir is
>
> location/mapset/.tmp/
>
> which you could link to the extra drive. This should be simplified for
> sure:
>
> Involved code:
> https://trac.osgeo.org/grass/browser/grass/trunk/lib/gis/file_name.c
> https://trac.osgeo.org/grass/browser/grass/trunk/lib/gis/tempfile.c
>
> Please open a ticket with the relevant info in it.
>
> > On a side note, r.terraflow should be an alternative for such a large
> > dataset, but from the manual:
> > "r.terraflow has a limit on the number of rows and columns (max 32,767
> > each)".
> > That's the size of a positive short integer. Is this limit still needed?
>
> I have no idea here, did you try it?
>
> Markus
>
>
> --
> Markus Neteler
> http://www.mundialis.de - free data with free software
> http://grass.osgeo.org
> http://courses.neteler.org/blog
>



-- 
Prof. Carlos Henrique Grohmann
Institute of Energy and Environment - Univ. of São Paulo, Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -

http://carlosgrohmann.com
http://orcid.org/0000-0001-5073-5572
________________
Can’t stop the signal.
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