[GRASS-dev] custom CRS

[Paulo van Breugel]

On 18-03-17 10:06, Paulo van Breugel wrote:
> Dear all,
>
> I have a shapefile which is in CRS ESRI:37203 [1], which is defined in 
> the prj file as
>
> GEOGCS["GCS_Everest_India_Nepal",DATUM["D_Everest_India_Nepal",SPHEROID["Everest_Definition_1962",6377301.243,300.8017255]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]] 
>
>
>
> The corresponding proj.4 definition (as defined in the esri epsg-codes 
> file in /usr/share/proj/)
>
> +proj=longlat +a=6377301.243 +b=6356100.230165384 +no_defs
>
> And when I create a location based on this shapefile, the projection 
> information is:
>
> -PROJ_INFO-------------------------------------------------
> name       : GCS_Everest_India_Nepal
> a          : 6377301.243
> es         : 0.006637846068423442
> proj       : ll
> no_defs    : defined
> -PROJ_UNITS------------------------------------------------
> unit       : degree
> units      : degrees
> meters     : 1.0
>
> Question 1: Now, I can import a shapefile or raster layer in 
> latlon/WGS84 (EPGS: 4326) without reprojection. GRASS thus assumes the 
> projection is identical, even if they are not? Why is that?
>
> The proj.4 definition above is missing the shift w.r.t. the WGS84. The 
> correct proj.4 definition for EPGS 37203 would be [2]
>
> +proj=longlat +a=6377301.243 +b=6356100.2284 
> +towgs84=295,736,257,0,0,0,0 +no_defs
>
> Question 2: In QGIS it is possible to define a custom CRS using the 
> above. Can I do this in GRASS as well, and if so, how? Or can / should 
> I add this to the datum information files in $GISBASE/etc/proj/ogr_csv?
>
>
> Regards,
>
> Paulo
>
>
> [1] https://epsg.io/37203
> [2] 
> https://disqus.com/home/discussion/qgistutorials/georeferencing_topo_sheets_and_scanned_maps/#comment-1426454689

A link that provides further relevant information

https://github.com/klokantech/epsg.io/issues/49


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