[GRASS-dev] custom CRS

[Benjamin Ducke]

On 18/03/17 12:15, Paulo van Breugel wrote:
> 
> 
> 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]]

[SNIP]

>> +proj=longlat +a=6377301.243 +b=6356100.2284
>> +towgs84=295,736,257,0,0,0,0 +no_defs

Are you sure that your "+towgs84" parameters are correct?
It seems to me that you intend to apply a three parameter
transformation, but you are specifying a seven parameter
transform with the scaling (last parameter) set to "0",
which might have unintended consequences.

To specify a three parameter datum transform:

+towgs84=295,736,257

If you really want to specify all seven parameters, but
want only the first three to take effect:

+towgs84=295,736,257,0,0,0,1

Best,

Ben

>>
>> 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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-- 
Dr. Benjamin Ducke
{*} Geospatial Consultant
{*} GIS Developer

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