[PROJ] Vertical grid transformation / ellipsoidal height to EGM2008 (EPSG 3855)

[Javier Jimenez Shaw]

Hola Inti

On Thu, 15 Sept 2022 at 22:18, inti luna <inti.luna.rsgis at gmail.com> wrote:

> Dear PROJ community,
> I am using a GNSS (Emlid REACH RS2 )to collect ground control points for
> drone mapping and supporting a project of monitoring vegetation after fire.
> I have collected data in LAT,LON (CRS EPSG 4326) and ellipsoidal height (m)
> and would like to transform it to another CRS. Target horizontal is EPSG:
> 25831 and target height is based on EGM2008 (EPSG 3855).
>
That RTK device should not produce vales in WGS84. The coordinates you
provide are in Spain. I would assume that the reference system used by the
base stations is ETRS89 (2D: EPSG:4258 , 3D EPSG:4937).
In addition to that, Spain has its own vertical CRS, Alicante height,
EPSG:5782
So probably your source CRS would be EPSG:4937 and destination
EPSG:25830+5782

> I just discovered PROJ and I am having issues with the vertical
> transformation.
>
> Using Linux Ubuntu 11 and installed PROJ using anaconda with:
>
Ubuntu 11?

> <conda install -c conda-forge proj>
>
> <conda install -c conda-forge proj-data>
>
> I tested with:
>
> <echo -2.69713764 43.37551925 | cs2cs +init=epsg:4326 +to +init=epsg:25830>
>
> which outputs: -2.69713764 43.37551925 which is fine.
>
> However, I don't understand very well how to perform the vertical grid
> shift.
>
> I tried:
>
> 1. <echo -2.69713764 43.37551925 102.635| cs2cs +init=epsg:4326
> +vgridshift  +to +init=epsg:25830 +grids=egm08_25.gtx>
>
> 2.<echo -2.69713764 43.37551925 102.635 | proj +init=epsg:4326
> +proj=vgridshift +grids=egm08_25.gtx>
>
This is working for me:
Using from WGS84 3D to EPSG:25830 + EGM2008
echo 43.37551925 -2.69713764 102.635 | PROJ_NETWORK=ON cs2cs EPSG:4979
EPSG:25830+3855
524534.95 4802561.48 53.07

Using from ETRS89 3D to EPSG:25830 + Alicante height
echo 43.37551925 -2.69713764 102.635 | PROJ_NETWORK=ON cs2cs EPSG:4937
EPSG:25830+5782
524534.95 4802561.48 53.72

PROJ_NETWORK=ON is not needed if proj-data is properly installed.

> But the first try ignores the height and the second got me an error
> message:
>
> "can't initialize operations that produce angular output coordinates
> program abnormally terminated"
>
> Thank you for your help,
>
> Inti
>
>
>
>
> --
> Inti Luna
> + 34 688756449
>
>
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>


.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.
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