[GRASS-user] r.terraflow on massive DEM

[Daniel Victoria]

Stephan, I'll give r.watershed a try and let it run for a couple of days.
Thanks

Thayer, I used r.recode because the person that sent me the data messed up
the null values. So in order to fix that I did:
1) use r.external to bring the data to Grass
2) fix null values with r.recode, which was faster than r.null

But I gave up on that path and since imported the data (r.in.gdal) and
fixed the null values with r.null.
I'm also using integer values (CELL type) because from what I heard, SRTM
does not provide floating point data.

Now I tried to run r.terraflow but I got a type error which asked me to use
r.terraflow.short. Since I don't have that command in my grass instalatin,
I converted the SRTM data to float. But that was to no avail since it's now
giving me a dimensions type overflow error and asking me to change the
dimension_type and recompile.

I'll give r.watershed a try. If that does not work, I'll see if I can
recompile.

Thanks
Daniel

On Mon, Jan 12, 2015 at 9:22 PM, Thayer Young <thayeray at yahoo.com> wrote:

> With regards to the size of DEM, if you can get the command to run it may
> take several days to finish, this is more than twice the size of the
> Washington State DEM that took the authors 33 hours in 2003 (Arge, Chase,
> Halpin, Toma, Urban, Vitter, Wickremesinghe  Efficient Flow Computation on
> Massive Grid Terrain Datasets Geoinformatica Volume 7 Issue 4, December
> 2003 Pages 283 - 313 ).  My mid-2014 computer runs at about twice the
> speed quoted in the paper.
>
> Did you r.recode it to make it smaller?  In flat areas you need the data
> contained after the decimal point to allow the flow a chance to make it
> down hill, otherwise you can get streams going no where near where they do
> in real life.  I have never tried running r.terraflow on an integer raster,
> I know that it works on decimal rasters.
>
> -Thayer
>
>
>
>  ------------------------------
>
> Date: Mon, 12 Jan 2015 09:59:40 -0200
> From: Daniel Victoria <daniel.victoria at gmail.com>
> To: grass <grass-user at lists.osgeo.org>
> Subject: [GRASS-user] r.terraflow on massive DEM
> Message-ID:
>     <CA+irsJjf7xhWgU968D+4+xc2YGJ=_n4xJtP0_WeU1ZpoRTt9ng at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
>
> Hi list,
>
> I'm trying to run r.terraflow on a very large DEM but I wander if it's
> __too large__.
>
> The region dimensions are:
> ncol=141114
> nrow=140487
> Data type = CELL
>
> The map is actually a reclass map of a raster that I imported using
> r.external.
>
> When I run r.terraflow I get:
>
> r.terraflow elevation=srtm_brasil at PERMANENT filled=srtm_fill
> direction=flowdir swatershed=sink accumulation=flowacc tci=srtm_tci
> directory=E:\terraflow_temp
>
> WARNING: raster srtm_brasil is of type CELL_TYPE --you should use
> r.terraflow.short
> ERROR: [nrows=140487, ncols=141114] dimension_type overflow -- change
> dimension_type and recompile
> (Mon Jan 12 09:57:18 2015) Command finished (0
> sec)
>
> However, I don't have an r.terraflow.short command
> I'm running Grass 7.0.0beta4 from OsGeo4W
>
> Cheers
> Daniel
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