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

[Javier Jimenez Shaw]

Italy? I am not aware of any Geoid grid file for Italy in PROJ-Data:
https://cdn.proj.org/

EPSG:5214 is the vertical coordinate reference system, not a geoid model.
https://epsg.org/crs_5214/Genoa-1942-height.html
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.



On Mon, 17 Oct 2022 at 10:59, Diogo <diogo at photopills.com> wrote:

> 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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