[GRASS-dev] custom CRS

[Paulo van Breugel]

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