On Mon, 17 Oct 2022, Diogo 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.
Sorry, I know no more (and probably less) than you about the transforms.
From what others have said, I suspect that there is no *meaningful*
way to have better elevation resolution over such a large area than the
Copernicus data.
I do know that 4326 uses a geoid which is less accurate *over Great
Britain* than the one the Great Britain Ordnance Survey have been
using for a century or two (OSGB36 Datum 1936, Airy Spheriod 1830!).
I suspect that other national geo-organisations do the same thing and you
will lose the extra accuracy in standardising on one coordinate system over
Europe.
Thanks again for your help,
Diogo
On Fri, 14 Oct 2022 at 15:57, Andrew C Aitchison <and...@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
and...@aitchison.me.uk
--
Andrew C. Aitchison Kendal, UK
and...@aitchison.me.uk
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