Grid transformation not taken into account when using gdaltransform (3.10) in command line (anaconda)

Question

I have installed GDAL-3.9.2-cp313-cp313-win_amd64.whl using Anaconda and I want to perform coordinate transformations with simple command lines using gdaltransform.

The issue I have is that the grid files needed for the transformation doesn't seem to be used.

Ex : I am trying to convert from WGS84 EPSG:4326 to WGS84 + EGM96 height EPSG:4326+5773

The command line I am using looks like this :

gdaltransform -s_srs EPSG:4326 -t_srs EPSG:4326+5773

If i look in the proj.db database I can located the expected grid file name WW15MGH.GRD. I have downloaded this file and installed it in multiple locations, but it never seems to be taken into account.

I have tried installing it in the same folder than the proj.db. I have tried setting up the environment variable PROJ_DATA and PROJ_LIB and put the grid file in this defined path. But it didn't make it work.

I am out of ideas now.

How can I spot what I am doing wrong?

Answer 1

EPSG:4326 is a 2D system and therefore height is not processed.

projinfo -s epsg:4326 -t epsg:4326+5773
Candidate operations found: 1
-------------------------------------
Operation No. 1:

unknown id, Inverse of Null geographic offset from WGS 84 to WGS 84, 0 m, World.

PROJ string:
+proj=noop

Try EPSG:4979 https://spatialreference.org/ref/epsg/4979/ instead

projinfo -s EPSG:4979 -t EPSG:4326+5773
Candidate operations found: 2
-------------------------------------
Operation No. 1:

unknown id, WGS 84 to EGM96 height (1), 1 m, World.

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +xy_out=rad
  +step +inv +proj=vgridshift +grids=us_nga_egm96_15.tif +multiplier=1
  +step +proj=unitconvert +xy_in=rad +xy_out=deg
  +step +proj=axisswap +order=2,1

Test with gdaltransform:

gdaltransform -s_srs EPSG:4979 -t_srs EPSG:4326+5773
Enter X Y [Z [T]] values separated by space, and press Return.
50 70 100
50 70 96.9851653575897