Daniel,
Before you go through the trouble of recompiling you may want to try
downloading a smaller SRTM DEM from Earth Explorer and make sure it works with
r.terraflow. I would recommend making sure r.terraflow works at all on your
system. Then scale up to the full mosaic and see if you still have a problem.
-Thayer
From: Daniel Victoria <[email protected]>
To: Charlie Shobe <[email protected]>
Cc: Thayer Young <[email protected]>; "[email protected]"
<[email protected]>
Sent: Tuesday, January 13, 2015 9:17 AM
Subject: Re: [GRASS-user] r.terraflow on massive DEM
Ouch! That means that probably, the person who imported the data, converted it
to integer without knowing...
Anyway, I'll still need to recompile r.terraflow if I'm to use on such a large
region (ncol=141114 x nrow=14048).
Thanks
Daniel
On Tue, Jan 13, 2015 at 12:12 PM, Charlie Shobe <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <[email protected]>
To: grass <[email protected]>
Subject: [GRASS-user] r.terraflow on massive DEM
Message-ID:
<CA+irsJjf7xhWgU968D+4+xc2YGJ=_n4xjtp0_weu1zportt...@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@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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