[Proj] Vertical Datum Shift

Andy Wilson wilson.andrew.j at gmail.com
Fri Dec 23 12:57:19 EST 2011

Hi Daniel.

I just joined the mailing list today so I don't think I can reply to
your message directly, but here goes.

You can get some useful information if you run cs2cs with debugging turned on:

PROJ_DEBUG=ON  cs2cs +proj=latlong +ellps=WGS84 +datum=WGS84
+geoidgrids=egm96_15.gtx +to +proj=latlong +ellps=WGS84 +datum=WGS84

It might be that that proj isn't finding your .gtx file, which needs
to be in PROJ_LIB which is likely /usr/share/proj/ or
/usr/local/share/proj/. I think the exact location is output when you
compile proj.

> I'm having trouble figuring out how to the the +geoidgrids option. I'm trying to
> convert EGM96 values to WGS84 with cs2cs (I will eventually be converting a dted
> file but first I'm trying to just get this to work) and I cannot get it to alter
> the values so I'm doing something wrong. Using 4.7.1.
> cs2cs +proj=latlong +ellps=WGS84 +datum=WGS84 +geoidgrids=egm96_15.gtx +to
> +proj=latlong +ellps=WGS84 +datum=WGS84
> It always outputs the exact same numbers I put in.
> Thanks.

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