[gdal-dev] Transformations with same horizontal datum but different geoid outputs the same Z value

[Diogo]

Hi Andrew. Thanks for taking the time to read my email and reply it.
I'm aware of Copernicus land and other datasets like SMRT3 and ASTER
however I need the best possible elevation resolution available. To do so,
I'm getting the elevation dataset directly from countries geographic
institutes and converting them into the coordinate system 4326+3855. But as
described in my previous email, I'm having some trouble with some geoids.
Do you have an idea why I'm having these transformation issues? To be
honest, I'm a bit lost because I can't understand it.

Thanks again for your help,
Diogo

On Fri, 14 Oct 2022 at 15:57, Andrew C Aitchison <andrew at aitchison.me.uk>
wrote:

> On Fri, 14 Oct 2022, Diogo wrote:
>
> > Hello everyone!
> >
> > I'm merging multiple elevation datasets from different countries and I
> > would like to re-project all into the same coordinates system, 4326+3855
> > using gdalwarp. I'm using `gdaltransform` to confirm that there is in
> fact
> > a conversion from the original projection to the aspected one. However,
> for
> > some datasets, there is only conversion in the XY axis, while the Z
> output
> > is the same as the input.
>
> Is there a good reason to start with these particular datasets ?
>
> There are international bodies who have produced elevation datasets
> covering the whole of
> Europe, eg
> https://land.copernicus.eu/user-corner/how-to-access-our-data
>
> https://www.eea.europa.eu/data-and-maps/data#c0=5&c11=&c5=all&b_start=0&c12=elevation
>
> https://www.eea.europa.eu/data-and-maps/data/copernicus-land-monitoring-service-eu-dem
>
> which would save you trying to stitch together data in different CRSes.
>
> > Below there are some examples (the geoid code is extracted from the
> dataset
> > documentation)
> >
> > Genoa 1942 height (Italy)
> >
> > $ echo "14.995 37.755 3357" | PROJ_NETWORK=ON gdaltransform --debug on
> > -s_srs "EPSG:4326+3855" -t_srs "EPSG:32632+5214">> 1028333.73796622
> > 4195591.29690422 3357
> >
> > N2000 (Finland)
> >
> > $ echo "25.15296 62.50195 269" | PROJ_NETWORK=ON gdaltransform --debug
> > on -s_srs "EPSG:4326+3855" -t_srs "EPSG:3067+3900">> 404861.868388335
> > 6931460.32557422 269
> >
> > EVRF2007 (Estonia)
> >
> > $ echo "27.059167 57.714444 318" | PROJ_NETWORK=ON gdaltransform
> > --debug on -s_srs "EPSG:4326+3855" -t_srs "EPSG:3301+5621">>
> > 682284.606829111 6401087.4159131 318
> >
> >
> > I don't have much experience with the projections and I'm a bit lost
> > to understand the possible issues, or interpreted the Z output. What
> > can be the possible issues?
> >
> > Any help would be appreciated.
> >
> > Best regards,
> >
> > Diogo
> >
>
> --
> Andrew C. Aitchison                      Kendal, UK
>                     andrew at aitchison.me.uk
>
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