[Proj] converting WGS84/ETRS89 to ITM/OSGM15

[Elmir Jagudin]

Hi

I'm trying to convert a WGS84/ETRS89 positions in Ireland into a ITM (Irish
Transverse Mercator) easting northings and OSGM15 elevations.

Using the this commands:

  echo -6.6 53 21 | /proj \
     +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=0.99982 +x_0=600000 +y_0=750000
+ellps=GRS80
     +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

gives me:

  693972.63    695281.52 21

The easting and northing are correct, however the elevation is not, the
correct value is -35.15.

Is it possible to use proj4 to calculate OSGM15 elevations? What should the
proj-string be in that case?

Or do i need to create a .gtx file for OSGM15?

Not sure how the elevations work in proj4, is there any documentation i
could read?


Thanks in advance,
Elmir
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