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

Mon Oct 17 03:03:35 PDT 2022

Hi,

Maybe there is no transformation for converting heights from N2000 into WGS84 heights registered into the EPSG database. I found only two N2000 related transformations EPSG:9573 and EPSG:9574 and they seem convert to EVRF2019 height.
Proj can convert between our national height systems N2000, N60, and N43 but I fear that we at the National Land Survey of Finland have not managed to register them yet.

This publication is too heavy to read for me but please have a look and contact Mirjam if you need more advice https://www.researchgate.net/publication/256481988_Development_of_the_Finnish_Height_Conversion_Surface_FIN2005N00#read

-Jukka Rahkonen-

Lähettäjä: gdal-dev <gdal-dev-bounces at lists.osgeo.org> Puolesta Diogo
Lähetetty: maanantai 17. lokakuuta 2022 11.59
Vastaanottaja: gdal-dev at lists.osgeo.org
Aihe: Re: [gdal-dev] Transformations with same horizontal datum but different geoid outputs the same Z value

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<mailto: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://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fland.copernicus.eu%2Fuser-corner%2Fhow-to-access-our-data&data=05%7C01%7Cjukka.rahkonen%40maanmittauslaitos.fi%7Caa18fc3bad0649824f9708dab01ed49b%7Cc4f8a63255804a1c92371d5a571b71fa%7C0%7C1%7C638015943753338265%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=mfo6NuPABxZJkU3MRQeYfLRAsV0TeX%2FlNkAlinnKN8w%3D&reserved=0>
https://www.eea.europa.eu/data-and-maps/data#c0=5&c11=&c5=all&b_start=0&c12=elevation<https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.eea.europa.eu%2Fdata-and-maps%2Fdata%23c0%3D5%26c11%3D%26c5%3Dall%26b_start%3D0%26c12%3Delevation&data=05%7C01%7Cjukka.rahkonen%40maanmittauslaitos.fi%7Caa18fc3bad0649824f9708dab01ed49b%7Cc4f8a63255804a1c92371d5a571b71fa%7C0%7C1%7C638015943753338265%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=1b7YhCgROWYUTq8TBXIivDLKmzEHuj5NpNRCW%2BeVQ%2Fg%3D&reserved=0>
https://www.eea.europa.eu/data-and-maps/data/copernicus-land-monitoring-service-eu-dem<https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.eea.europa.eu%2Fdata-and-maps%2Fdata%2Fcopernicus-land-monitoring-service-eu-dem&data=05%7C01%7Cjukka.rahkonen%40maanmittauslaitos.fi%7Caa18fc3bad0649824f9708dab01ed49b%7Cc4f8a63255804a1c92371d5a571b71fa%7C0%7C1%7C638015943753338265%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=PKBB6EfcZ5qniFw6gKkcENOzoPvnfTiQr53ErOZV4DA%3D&reserved=0>

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<mailto:andrew at aitchison.me.uk>
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