[Proj] tmerc "folding back" far from the central meridian

Frank Warmerdam warmerdam at pobox.com
Tue Jun 17 12:45:41 EDT 2008

Folks (mostly Gerald),

The tmerc projection has a tendency to fold back on itself when you get
really far from the central meridian.  This causes problems when applications
naively try to reproject locations from all around the world into transverse
mercator without regard to appropriateness.

What I would like is if we could make the tmerc projection fail (ie return
HUGE_VAL) for points so far from the central meridian that they are likely
to start folding back on themselves.

Is this a reasonable idea?  What longitude range would be suitable?
Should we make this conditional on some extra parameter in the projeciton
definition?  I have a ticket at:


For my client, I'll likely try something like limiting things to a 60
degree swath centered on the central meridian.  But I'd like input on a
more systematic approach.

I'd add that I'm investigating this with regard to tmerc, but similar
issues must exist for some other projections.

Best regards,
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

More information about the Proj mailing list