[Proj] GTX format

[nicolas david]

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 :
  http://vdatum.noaa.gov/dev/gtx_info.html#dev_gtx_binary

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
http://gitorious.org/proj4-sandbox/proj4-cmake/blobs/ign/proj/src/ign2gtx.c)

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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