[Proj] patch: fallback to 7/3 param transform when gridshift transform fails

[Craig de Stigter]

Hi list

We came across some out-of-grid geometries when transforming from EPSG:27200
(New Zealand Map Grid). The results returned included INFs and NANs, which
was hardly useful.

As a solution I wrote a patch for the pj_datum_transform function in Proj.
The patch first tries to convert coordinates using the gridshift approach if
available, but on failure will fall back to using the appropriate 3- or
7-parameter transform.

The Bugzilla page linked from http://www.remotesensing.org/proj/ is not
working, so I've attached the patch to this message for your perusal.
Comments are welcome.

Regards
Craig de Stigter

-- 
Koordinates Ltd (formerly One Track Mind).
PO Box 1604, Shortland St, Auckland, New Zealand
Phone +64-9-966 0433 Fax +64-9-969 0045
Web http://www.koordinates.com
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