[GRASS-user] Re: problem using r.watershed

[Markus Metz]

On Sun, Mar 25, 2012 at 2:59 PM, Filipe Silva Dias
<filipesdias at gmail.com> wrote:
> Thanks. Out of curiosity and tried with Grass 7 with -m (and 30 m
> resolution) and I obtained this error message:
>
> r.watershed -m elevation=DemPT2 at Grass7 threshold=10000
> stream=streams
> SECTION 1 beginning: Initiating Variables. 5 sections total.
> SECTION 1a: Mark masked and NULL cells
> SECTION 1b: Determining Offmap Flow.
> SECTION 2: A* Search.
> SECTION 3: Accumulating Surface Flow with MFD.
> SECTION 4: Watershed determination.
> SECTION 5: Closing Maps.
> ERROR: Rast_make_random_colors: min (1) > max (0)

Apparently no basins were determined, probably because the threshold
of 10000 for flow accumulation was never reached. Maybe the current
region was either too small or did not cover parts of the DEM DemPT2?

BTW, if you want to try out GRASS 7 in a separate mapset, you don't
need to copy over the DEM if you just want to read it. Within the
mapset Grass7, the following commands should work:
g.region -p rast=DemPt at ETRS89
r.watershed elevation=DemPt at ETRS89 stream=stream threshold=10000 -m

Markus M

>
> Subprocess failed with exit code 1
> category information for [streams] in [Grass7] missing or invalid
>
>
>
>
> On Sun, Mar 25, 2012 at 11:49 AM, Markus Metz
> <markus.metz.giswork at googlemail.com> wrote:
>>
>> On Sun, Mar 25, 2012 at 12:30 PM, Filipe Silva Dias
>> <filipesdias at gmail.com> wrote:
>> > I switched the resolution from 30x30 to 100x100 and now it works.
>> > Problem
>> > solved.
>> >
>> >
>> > On Sun, Mar 25, 2012 at 11:12 AM, Filipe Silva Dias
>> > <filipesdias at gmail.com>
>> > wrote:
>> >>
>> >> I'm using GRASS 6.4.2 and I'm on Windows 7
>> >>
>> >>
>> >> On Sun, Mar 25, 2012 at 11:11 AM, Filipe Silva Dias
>> >> <filipesdias at gmail.com> wrote:
>> >>>
>> >>> Dear all
>> >>>
>> >>> I'm trying to run r.watershed on a ASTER DEM (with the size of
>> >>> Portugal)
>> >>> but I'm getting this error:
>> >>>
>> >>> r.watershed elevation=DemPt at ETRS89 stream=stream
>> >>> threshold=10000
>> >>> SECTION 1a (of 5): Initiating Memory.
>> >>> ERROR: G_malloc: unable to allocate 1515173064 bytes at
>> >>> init_vars.c:134
>> >>> Subprocess failed with exit code 1
>> >>> category information for [stream] in [ETRS89] missing or invalid
>> >>>
>> >>> What am I doing wrong?
>> >>>
>> As you figured out already, the region, i.e. number of cells was too
>> large. In order to run r.watershed with that region (Portugal at 30m
>> resolution) on Windows, you would need GRASS 7 and run r.watershed
>> with the -m option.
>>
>> Markus M
>
>