[Gdal-dev] python CoordinateTransformation

[Frank Warmerdam]

Xiaodong Zhang wrote:
> Thanks Frank and Howard,
> 
> It works. Just curious to know a little bit of CloneGeogCS() method, the 
> description of which is not available from the gdal web. Is it designed 
> to create a geographic projection (i.e., lat & long) out of the existing 
> projection using the same, say, datum, etc.

Xiaodong,

Yes.  The Geographic coordinate system includes the ellipsoid, datum,
shift to wgs84, prime meridian and angular units.  Projected coordinate
systems are based on a geographic coordinate system.  CloneGeogCS() creates
a new geographic coordinate system capturing the geographic coordinate system
of the source geograhpic or projected coordinate system.

For a projected coordinate system like this:
PROJCS["WGS_1984_UTM_Zone_11S",
     GEOGCS["GCS_WGS_1984",
         DATUM["D_WGS_1984",
             SPHEROID["WGS_84",6378137,298.257223563]],
         PRIMEM["Greenwich",0],
         UNIT["Degree",0.017453292519943295]],
     PROJECTION["Transverse_Mercator"],
     PARAMETER["latitude_of_origin",0],
     PARAMETER["central_meridian",-117],
     PARAMETER["scale_factor",0.9996],
     PARAMETER["false_easting",500000],
     PARAMETER["false_northing",10000000],
     UNIT["Meter",1]]

The Geographic coordinate system would be:

     GEOGCS["GCS_WGS_1984",
         DATUM["D_WGS_1984",
             SPHEROID["WGS_84",6378137,298.257223563]],
         PRIMEM["Greenwich",0],
         UNIT["Degree",0.017453292519943295]],

Best regards,
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