[Geotiff] Polar Stereographic, GeoTIFF & ProjScaleAtCenterGeoKey

[Moore, Dave M (UK Rochester)]

Hi All,
I'm having 'fun' with GeoTIFF and Polar Stereographic projections. My
problem appears to be associated with the 'scale factor' attribute of
this projection. It appears that using the ProjScaleAtCenterGeoKey key
makes no difference to the output file irrespective of the value I give
it (at least when viewed in Global Mapper and other GeoTIFF viewers). 
 
This issue has come about because my GeoTIFF output files for the polar
regions appear to have a small error in the scaling (of the order of
about 0.992) which just happens to be the average scaling factor for a
polar stereographic projection for over 80 degrees
(http://en.wikipedia.org/wiki/Universal_Polar_Stereographic_coordinate_s
ystem). I thought I could apply this scaling through the
ProjScaleAtCenterGeoKey key on the geotiff library but irrespective of
the value, it appears to make no difference when I view the file. I have
applied the scale factor manually to the tiepoint and pixscale values
which works but it would be better to apply it through the key IMO.
 
Any ideas why the output file does not respond to the
ProjScaleAtCenterGeoKey?. An example would be nice. Thanks in advance
for any comments or suggestions.
 
Dave
 

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