[postgis-users] What is the proj4text for this .prj entry

[Robert Coup]

Hiya,

On Sat, Mar 14, 2009 at 11:28 AM, Paul Ramsey <pramsey at opengeo.org> wrote:

> Since I can't verify, I'll just give you my guess:
>
> +proj=merc +lat_ts=-46 +lon_0=100 +x_0=0 +y_0=0 +ellps=clrk66
>

Some working behind Paul's "guess" (via Python+GDAL)....

from osgeo.osr import SpatialReference
s = SpatialReference()

s.ImportFromWkt('PROJCS["Clarke_1866_Mercator",GEOGCS["GCS_Clarke_1866",DATUM["D_Clarke_1866",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Mercator"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",100.0],PARAMETER["Standard_Parallel_1",-46.0],UNIT["Meter",1.0]]')
>>> 0

s.ExportToProj4()
>>> ERROR 6: No translation for Mercator to PROJ.4 format is known.

s.ImportFromWkt('PROJCS["Clarke_1866_Mercator",GEOGCS["GCS_Clarke_1866",DATUM["D_Clarke_1866",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],
PROJECTION["Mercator_2SP"]
,PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",100.0],PARAMETER["Standard_Parallel_1",-46.0],UNIT["Meter",1.0]]')
>>> 0

s.ExportToProj4()
'+proj=merc +lon_0=100 +lat_ts=-46 +x_0=0 +y_0=0 +ellps=clrk66 +units=m
+no_defs '


Mercator 2SP seems to be what you want: you have a latitude & a longitude
instead of a longitude and a scale (1SP).
http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html

HTH,

Rob :)
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