[Geotiff] Essential information found in the citations

[Mathieu.St-Pierre at bentley.com]

Hi all, 

 

I have found some GeoTIFF files for which a PCS or GCS cannot be found
if the information contained in the citation keys aren't processed.

 

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. 

 

      GTModelTypeGeoKey (Short,1): ModelTypeProjected

      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea

      GeographicTypeGeoKey (Short,1): Unknown-32768

      GeogGeodeticDatumGeoKey (Short,1): Datum_WGS84

      GeogEllipsoidGeoKey (Short,1): Ellipse_WGS_84

      ProjectedCSTypeGeoKey (Short,1): User-Defined

      PCSCitationGeoKey (Ascii,47): "Space Oblique Mercator-preset
satellites WGS84"

      ProjectionGeoKey (Short,1): User-Defined

      ProjCoordTransGeoKey (Short,1): User-Defined

      ProjLinearUnitsGeoKey (Short,1): Linear_Meter

      ProjNatOriginLongGeoKey (Double,1): 76.7733936       

      ProjNatOriginLatGeoKey (Double,1): 0   

 

 

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"

      GeogGeodeticDatumGeoKey (Short,1): User-Defined

      GeogPrimeMeridianGeoKey (Short,1): PM_Greenwich

      GeogLinearUnitsGeoKey (Short,1): Linear_Meter

      GeogAngularUnitsGeoKey (Short,1): Angular_Degree

      GeogEllipsoidGeoKey (Short,1): User-Defined

      GeogSemiMajorAxisGeoKey (Double,1): 6378137          

      GeogSemiMinorAxisGeoKey (Double,1): 6356752.31       

      ProjectedCSTypeGeoKey (Short,1): User-Defined

      PCSCitationGeoKey (Ascii,236): "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 = Albers Conical Equal Area"

      ProjectionGeoKey (Short,1): User-Defined

      ProjCoordTransGeoKey (Short,1): CT_AlbersEqualArea

      ProjLinearUnitsGeoKey (Short,1): Linear_Meter

      ProjStdParallel1GeoKey (Double,1): 34               

      ProjStdParallel2GeoKey (Double,1): 40.5             

      ProjNatOriginLatGeoKey (Double,1): 0                

      ProjFalseEastingGeoKey (Double,1): 0                

      ProjFalseNorthingGeoKey (Double,1): -4000000         

      ProjCenterLongGeoKey (Double,1): -120     

 

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?

 

Thanks, 

 

Mathieu

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