[GRASS-user] define a region by 2 epsg

GRASS GRASS user
,
1

Please keep the thread on the list.

Yes I think it's inappropriate to split a watershed into 2 parts if you
want to model the whole thing as one. You are likely going to do better
finding a single projection that covers your entire area of interest.

-Alex

On 03/16/2016 10:20 AM, Mourad Boutouchent wrote:

IS it wrog if I split up my DEM in two parts, the 1st one in the UTM21N and the rest in the UTM22N then I can run Grass hydrological moudles (r.watershed and r.water.outlet among other) on each DEM and finally merge them in GRASS or QGIS. Think you this is an appropriate way to do it?

------------------------------------------------------------------------------------
Mourad Boutouhent
Laboratoire de Mathématiques Informatique et Applications
Université de Guyane
Tél : 06 63 81 50 29

--------------------------------------------
En date de : Mer 16.3.16, Alex Mandel <tech_dev@wildintellect.com> a écrit :

Objet: Re: [GRASS-user] define a region by 2 epsg
À: "Mourad Boutouchent" <mourad.boutouchent@yahoo.fr>, grass-user@lists.osgeo.org
Date: Mercredi 16 mars 2016, 16h50

How far into the second
UTM Zone does your region go? If not far and the
distortion is acceptable you can reproject 1
into the other.

Otherwise
you need to find or create a Projection that does a better
job
of covering your region. A UTM
projection is unlikely to be a good
candidate in this case. Do you care more about
preserving Area or
Distance measures (that
will help you pick an appropriate projection).

So, no, you can not use 2 EPSG
codes at the same time, you have to
convert
the data into a common projection.

Thanks,
Alex

On 03/16/2016 08:10 AM, Mourad Boutouchent
wrote:
> I'm working on watershed
hydrology, then I went to obtain drainage direction,
accumulation zones, streams system and elementary watersheds
of a study area. However I work on an area which belong to 2
EPSG (EPSG 3313 and EPSG 2972).
>
> I download all the SRTM tiles of the study
area and have filled the voids. I merged these tiles and
projected the result in the EPSG 2972 (initially WGS84). Of
course, a part of the DTM has negative EAST coordinates
which cause errors when assinging region and running
r.watershed and r.water.outlet.
> I tryed
to work in WGS84 but still r.water.outlet does not work.
>
> Is it possible to
define a region with two EPSG? How achieve r.water.outlet
with success
> I'm quite locked...Any
help ?
>
>
------------------------------------------------------------------------------------
> B.Mourad
>
Laboratoire de Mathématiques Informatique et
Applications
> Université de Guyane
> Tél : 06 63 81 50 29
>
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