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

[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.

Derek





On Fri, Apr 1, 2016 at 12:18 PM, Andre Joost <andre+joost at nurfuerspam.de>
wrote:

> Am 31.03.2016 um 17:16 schrieb Derek Stuart:
>
>> I am using GDAL routines as part of RAS Mapper within HEC-RAS.   I
>> am coming from ArcMap where I am using a custom transformation GTF
>> file to translate from the D_Everest_Bangladesh datum to WGS_1984.
>>
>> The GTF file includes the following:
>>
>>
>> GEOGTRAN["ever2wgs",GEOGCS["GCS_Everest_Bangladesh",DATUM["D_Everest_Bangladesh",SPHEROID["Everest_Adjustment_1937",6377276.345,300.8017]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],METHOD["Geocentric_Translation"],PARAMETER["X_Axis_Translation",283.729],PARAMETER["Y_Axis_Translation",735.942],PARAMETER["Z_Axis_Translation",261.143]]
>>
>>
> The parameters seem to be identical with EPSG:4682 Gulshan 303:
>
> +proj=longlat +a=6377276.345 +b=6356075.41314024
> +towgs84=283.7,735.9,261.1,0,0,0,0 +no_defs
>
> So just assign that CRS and see if the data fits to other data sources,
> like Openstreetmap.
>
> HTH,
> André Joost
>
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-- 
Derek
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