[Gdal-dev] Coordinate transform problem

[Frank Warmerdam]

Chapman, Martin wrote:
> Ok, I figured it out.  I had numerous things wrong in my code outside 
> this function.  I still have one problem though.  The Transform method 
> of the OGRCoordinateTransformation class doesn't like it when I pass in 
> coordinates that are outside the valid limit for certain projections 
> (i.e. Mercator).  My new question is, how do I calculate what the valid 
> limits are for a projection like mercator?  Is it a matter of 
> subtracting False Easting and Northing or something like that?  Any help 
> on understanding how to calculate these limits for a projection would be 
> much appreciated.

Martin,

I am not aware of any systematic way of determining bounds of validity
for projections.  Note that in many cases the projectinos equations
degrade gradually so there is no obvious bound.  It depends on your
error tolerance.  But even at that, there is no GDAL/OGR/PROJ support
for determining error or regions of appropriateness.

Best regards,
-- 
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