[Gdal-dev] OGR, PROJ.4, and handling of Datum

[Ben Discoe]

(Replying to myself..)

> Question #1: What is this ntv2_0.gsb file?  If PROJ looks for it,
> why is it not included with the standard PROJ distribution data?

Sorry about that question, i was able to answer it with a Google search for
"ntv2_0.gsb".  Apparently is a large (14MB) proprietary Datum shift file
specifically for Canada.  So, it is quite unrelated to why my data point in
Panama is failing.

So, the more important question is #2.  The gist of this is, how can i as a
user of OGR find out when OGR/PROJ has failed to produce a viable
transformation.

> Now, on to OGR.  When i use OGRCreateCoordinateTransformation()
> for the same transformation as above, it cheerfully gives me an
> OGRCoordinateTransformation object which proceeds to perform
> totally bogus conversions.
>
> Question #2: Since PROJ is clearly failing in this case, shouldn't
> OGRCreateCoordinateTransformation fail, i.e. return NULL?  Is
> this a lack of error-checking in OGR, PROJ, or both?
>
> Thanks,
> Ben