[GRASS-user] r.terraflow on massive DEM

[Daniel Victoria]

Charlie,

I just downloaded some SRTM 1arc sec. from EarthExplorer. The data is
supplied in 3 different file types, GeoTIFF, DTED or BIL and they are all
in Integer values (Int16). No floating point elevation values.

Cheers
Daniel

On Tue, Jan 13, 2015 at 12:12 PM, Charlie Shobe <chsh5846 at colorado.edu>
wrote:

> Hi Daniel,
>
> I believe that SRTM data does in fact provide floating point elevation
> values, so you may want to try working with the DEM as type FCELL from the
> very beginning. I don't know if this will help solve your problem, but the
> last time I brought in SRTM (1 arc second) data it was type FCELL and
> contained several decimal places of precision.
>
> Good luck,
>
> Charlie
>
>
> On Jan 13, 2015, at 4:00 AM, Daniel Victoria <daniel.victoria at gmail.com>
> wrote:
>
> 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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