4 Extended GeoTIFF

This section is for future development TBD.
Possible additional GeoKeys for Revision 2.0:
   PerspectHeightGeoKey   (General Vertical Nearsided Perspective)
   SOMInclinAngleGeoKey   (SOM)
   SOMAscendLongGeoKey    (SOM)
   SOMRevPeriodGeoKey     (SOM)
   SOMEndOfPathGeoKey     (SOM)  ? is this needed ?  SHORT
   SOMRatioGeoKey         (SOM)
   SOMPathNumGeoKey       (SOM)    SHORT
   SOMSatelliteNumGeoKey  (SOM)    SHORT
   OEAShapeMGeoKey        (Oblated Equal Area)
   OEAShapeNGeoKey        (Oblated Equal Area)
   OEARotationAngleGeoKey (Oblated Equal Area)
Other items for consideration:
o Digital Elevation Model information, such as Vertical Datums, Sounding Datums.
o Accuracy Keys for linear, circular, and spherical errors, etc.

o Source information, such as details of an original coordinate system 
  and of transformations between it and the coordinate system in which 
  data is being exchanged.