[GRASS-user] define a region by 2 epsg

[Alex M]

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 at wildintellect.com> a écrit :
> 
>  Objet: Re: [GRASS-user] define a region by 2 epsg
>  À: "Mourad Boutouchent" <mourad.boutouchent at yahoo.fr>, grass-user at 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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