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
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