[gdal-dev] Setting up GDAL Custom Transformation from ESRI GTF File

[Andre Joost]

Am 03.04.2016 um 14:05 schrieb Derek Stuart:
> Andre: The only Gulshan coordinate system I see with EPSG 4682 is a
> geographic coordinate system.  I am using a projected coordinate
> system called BTM. This is a fairly new coordinate system, but it is
> the standard here in Bangladesh.
>
> PROJCS["BTM",GEOGCS["GCS_Everest_Bangladesh",DATUM["D_Everest_Bangladesh",SPHEROID["Everest_Adjustment_1937",6377276.345,300.8017]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",-2000000.0],PARAMETER["Central_Meridian",90.0],PARAMETER["Scale_Factor",0.9996],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]
>
>  There is a projected coordinate system called Gulshan 303 Bangladesh
> TM that uses the Gulshan datum, but it has EPSG 3106, not 4682.
>
> PROJCS["Gulshan_303_Bangladesh_TM",GEOGCS["GCS_Gulshan_303",DATUM["D_Gulshan_303",SPHEROID["Everest_Adjustment_1937",6377276.345,300.8017]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",90.0],PARAMETER["Scale_Factor",0.9996],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0],AUTHORITY["EPSG",3106]]
>
>  This has very similar parameters to BTM, except that Gulshan 303 has
> a false northing of 0 and BTM has -2000000.0.  I asked some other
> GIS professionals locally and was told that here isn't a EPSG code
> that matches BTM.  Unless I want to reproject my data and work in
> UTM, I don't see a way to avoid adding a custom transformation to
> GDAL.

Your first post did not include information on the projected coordinate 
system. Since it has a different false Northing, you really have to put 
up a custom CRS. But you have to take the +towgs84 parameter set to 
shift from the Everest ellipsoid to WGS84. The WKT definitions you give 
do not include that, because the ARCGIS world handles datum 
transformations separately.

You can put the WKT definition above in a text file, and run gdalsrsinfo 
on that file. It will report:

+proj=tmerc +lat_0=0 +lon_0=90 +k=0.9996 +x_0=500000 +y_0=-2000000 
+a=6377276.345 +b=6356075.41314024 +units=m +no_defs

As mentioned above, add the +towgs84 set for Gulshan, which you find in 
EPSG:4682:

+proj=tmerc +lat_0=0 +lon_0=90 +k=0.9996 +x_0=500000 +y_0=-2000000 
+a=6377276.345 +b=6356075.41314024 +towgs84=283.7,735.9,261.1,0,0,0,0 
+units=m +no_defs

HTH,
André Joost