[Proj] proj-4 introduced errors!

[Frank Warmerdam]

support.mn at elisanet.fi wrote:
> To: proj at lists.maptools.org
> 
> PJ_Transform_Plus() or similar....
> 
> Is there any plan to add a new routine to the library (PJ_Transform_Plus 
> or similar), that would do the datum conversion more elegantly? Current 
> version intoduces datum shits to transformations where usually such 
> shits are not seen! Let's have an example:
> 
> Datum 1:
> 
> proj=robin
> ellps=WGS84
> datum=WGS86
> no_defs
> 
> Datum 2:
> 
> proj=tmerc
> ellps=WGS84
> datum=WGS86
> no_defs

Folks,

For reference, the reason a problem occurs is that internally the ellipse
for robinson is reset to a sphere since it is a spherical only projection.
Unfortunately the datum/ellipse shift code then picks up on this difference
and attempts an ellipse to ellipse conversion.

This is definately not desirable, but I'm not sure how to fix it.  And
somehow Janne's approach is such that I don't feel like putting everything
else aside to work on the issue.

Good solutions welcome.

Best regards,
-- 
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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