[Proj] GTX format

nicolas david ericnico.david at gmail.com
Sun Jan 8 04:49:35 EST 2012

Hi Michal

But I have no idea how to create and install gtx file with geoid data?

the gtx file description could be found on vdatum noaa pages :

some Vertical Datum could be found on http://download.osgeo.org/proj/vdatum/
You need to install them on the same directory as your proj nad file (
directory containing nadgrid data, EPSG dictionnary etc..).
Look at your PROJ_LIB environnement Variable for the path of this directory.

> Is there something like geo2bin? To compile text data in binary format?
I'm not aware of such utilities, for french geoidgrids I have to write my
own utilitiy to convert from french geoid format to gtx format (you could
look this code on gitorious

When your write "text data" do you mean like *.lla file ?

> How to aware proj that new gtx file exists and where?
A) add theses gtx files on your nad directory ( PROJ_LIB envVar)
B) add the "+geoidgrids" option on your proj description

Nicolas DAVID
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