[Geotiff] Essential information found in the citations

[Frank Warmerdam]

Mathieu.St-Pierre at bentley.com wrote:
> The first kind of information that I’ve found packed in the citation key 
> PCSCitationGeoKey is the coordinate transformation method. As an 
> example, the keys below have been found in some GeoTIFF file I got.

...
>       PCSCitationGeoKey (Ascii,47): "Space Oblique Mercator-preset 
> satellites WGS84"
...
> The second kind of information that I’ve found packed in the citation 
> key GeogCitationGeoKey is the datum and ellipsoid names. As an example, 
> the keys below have been found in some GeoTIFF file I got. Note that in 
> this example, there is also other relevant information in the other 
> citation keys, but these information are already in other non citation 
> GeoTIFF keys.
> 
>  
> 
> GTModelTypeGeoKey (Short,1): ModelTypeProjected
> 
>       GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
> 
>       GTCitationGeoKey (Ascii,274): "IMAGINE GeoTIFF Support\nCopyright 
> 1991 - 2005 by Leica Geosystems Geospatial Imaging, LLC. All Rights 
> Reserved\n@(#)$RCSfile: egtf.c $ IMAGINE 9.0 $Revision: 10.0 $ $Date: 
> 2005/07/26 15:10:00 EST $\nProjection Name = NAD_1983_HARN_Albers\nUnits 
> = meters\nGeoTIFF Units = meters"
> 
>       GeographicTypeGeoKey (Short,1): User-Defined
> 
>       GeogCitationGeoKey (Ascii,297): "IMAGINE GeoTIFF 
> Support\nCopyright 1991 - 2005 by Leica Geosystems Geospatial Imaging, 
> LLC. All Rights Reserved\n@(#)$RCSfile: egtf.c $ IMAGINE 9.0 $Revision: 
> 10.0 $ $Date: 2005/07/26 15:10:00 EST $\nUnable to match Ellipsoid 
> (Datum) to a GeographicTypeGeoKey value\nEllipsoid = GRS 1980\nDatum = HARN"
...
> As I understand, to use of the citation keys to store essential 
> information is a mean to cope with the limitation of the GeoTIFF standard.
> 
> So are some of you aware of some non-official standard or accepted 
> practice regarding the storing of information in citation keys?

Mathieu,

I am not aware of any accepted practice in interpreting the citations
to extract information.  Clearly these are underspecified GeoTIFF files.
You pretty much need to handle them on a per-generator basis if you want
to extract anything from the citations.  I generally just try to carry
the citations through to the user so they can interprete them and
reset coordinate system info.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org