[gdal-dev] (Swiss) SPOT projection - not able to identify it

[Frank Warmerdam]

Stefan Schwarzer wrote:
> Hi there,
> 
> I have a SPOT image for some part of Switzerland. The metadata are a bit 
> vague, it's saying:
...
> The GDALINFO gives me this:
> 
> gridmac7:~ schwarzer$ 
> /Library/Frameworks/GDAL.framework/Versions/1.4/Programs/gdalinfo 
> /Volumes/couvagl/data/source\ data/SPOT/tif/SITL-Spot-5m-RGB.tif
> Driver: GTiff/GeoTIFFSize is 13000, 12000
> Coordinate System is:
> PROJCS["OM          D514",
>     GEOGCS["unnamed",
>         DATUM["unknown",
>             SPHEROID["unretrievable - using WGS84",6378137,298.257223563]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433]],
>     PROJECTION["Hotine_Oblique_Mercator"],
>     PARAMETER["latitude_of_center",46.95240555555556],
>     PARAMETER["longitude_of_center",7.439583333333333],
>     PARAMETER["azimuth",90],
>     PARAMETER["rectified_grid_angle",90],
>     PARAMETER["scale_factor",1],
>     PARAMETER["false_easting",600000],
>     PARAMETER["false_northing",200000],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]]]
...
> But what kind of projection is this? 
> 
> Normally I would have said it's in the national system, which is CH1903 
> has the same Projection parameters. But I am confused due to
> 
> 1. PROJCS["OM          D514"
> 2. GEOGCS["unnamed"
> 3. DATUM["unknown",
> 
> also, the metadata are talkingabout WGS84....
> 
> Can some one clear the picture for me please?

Stefan,

I imagine this is intended to be CH1903.  The PROJCS name "OM     D514"
indicates that this is a PCI generated TIFF file (from Spot!) and based on
my intimate knowledge of that GeoTIFF writer I suspect it is not writing
out the normal EPSG datum code for the file so GDAL ends up with "unnamed".

It might be interesting to see a "listgeo" report on this file.

BTW, I'm not positive that Hotine Oblique Mercator is really the best way
to translate Swiss Oblique Mercator.  I'm not sure if this will invalidate
reprojection results within GDAL or not.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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