[gdal-dev] Using a specific earth model

[Frank Warmerdam]

Andrea Battisti wrote:
> Hi list!
> 
> 
> I am testing a geotiff file which is in the following coordinate system
> (from gdalinfo...):
> 
> 
> Coordinate System is:
> PROJCS["SIN         E019",
>     GEOGCS["unnamed",
>         DATUM["unknown",
>             SPHEROID["unretrievable - using WGS84",6378137,298.257223563]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433]],
>     PROJECTION["Sinusoidal"],
>     PARAMETER["longitude_of_center",-82],
>     PARAMETER["false_easting",0],
>     PARAMETER["false_northing",0],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]]]
> 
> 
> 
> The earth model used in the "SIN E019" should be an ideal sphere with
> radius (m): 6370997, but it is not recognized and the WGS84 is used instead.
> This leads to unwanted offsets on the projected image.
> 
> Is there a way to tell GDAL to use a specific model when it encounters a
> specific coordinate system?

Andrea,

Briefly, no.  There is no way to have GDAL recognise something like
"SIN     E019" and override the SPHEROID.  But there are ways of manually
overriding the coordinate system on a file.  For instance, create a
well known text file of the coordinate system you want to use and doing:

   gdal_translate in.pix -a_srs fixed.wkt out.tif

The above coordinate system was obviously originally from PCI.  Did you
get it directly from a PCIDSK file, or from an intermediate GeoTIFF file?
the gdal/ogr/ogr_srs_pci.cpp code already knows that E019 is a normal
sphere, so I would expect it to get expanded properly if coming from
a PCIDSK file (or anything else like PAux using pci coordinate system
translation).

If it came from a GeoTIFF file, then I would have expected PCI to write
the proper spheroid info into the geotiff file, and for GDAL to pick it
up.  If this is the situation, I'd appreciate seeing a "listgeo" report
on the file.  Listgeo is part of libgeotiff and should be available in
FWTools distributions.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent