[postgis-devel] Issue 89 in postgis: transform() grid-shift 2nd chance logic defective

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Comment #8 on issue 89 by william.... at acm.org: transform() grid-shift 2nd  
chance logic defective
http://code.google.com/p/postgis/issues/detail?id=89

Thanks, Frank.  I hadn't dug that deeply into proj (and thanks for all you  
do there
and on GDAL).  I can hardly do otherwise than gratefully embrace your  
analysis and
conclusion.  However ...

1. It would be really nice if proj.4 error handling clearly distinguished  
between
missing grid-shift files and transformed points outside the range for which  
the grid
shift is defined.

2. The "second chance" logic in PostGIS's lwgeom_transform.c should be  
entirely
removed.  It does not do what its comments claim, and, if it did, would  
conflict
with the approach you recommend above.

3. It would be helpful to improve PostGIS warning/error messages as I  
suggest in the
next to last paragraph of my last message above, at least to the extent  
still
relevant with your recommended approach.

I'll be happy to take a swipe at patches for items 2 and 3 above, though  
given my
limited C coding skills, it would probably be better for the PostGIS  
development
team to do so if resources are available.

-- Bill

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