[GRASS-user] NASADEM: new global 1 arcsec DEM

[Robert Nuske]

Hi Markus,

>> did you use the NASADEM further than importing it in GRASS?
> 
> Well, I used it like a DEM..

That's good to know.
I find it hard to find any applications using this data set. Seems to be
still early and r.in.nasadem a frontrunner ;-)


>> I need a DEM for Germany + 10km Buffer. So, I thought NASADEM would be a natural fit and am now trying to get a handle on this dataset.
>>
>> The import with r.in.nasadem in a WGS84 Location just worked.
>> Thanks a lot metzm!
>>
>> The NASADEM documentation states, that the height of the merged DEM (NASADEM_HGT) is above EGM96 geoid and not WGS84 ellipsoid. I have no clue how to get from there to UTM32 with a height reference common in Germany (DHHN92).
>>
>>
>> Do you have any solutions or hints how to proceed?

> According to the answer here
> https://gis.stackexchange.com/questions/361240/are-wgs84-latlon-coordinates-and-egm96-latlon-coordinates-the-same-and-differenc
> 
> the math would be a r.mapcalc formula.

This seems to be the transformation from orthometric heights
(approximately mean sea level) to ellipsoid heights.

According to wikipedia [1] EGM96 is also part of WGS84. WGS84 has two
reference heights the geoid EGM96 and the ellipsoid (now also named
WGS84). This makes the communication about it quite tricky.


> Time ago I played with
> https://grasswiki.osgeo.org/wiki/Global_datasets#EGM2008_Geoid_Data_.28Earth_Gravitational_Model.29
> 
> The EGM96 data appear to be here as interpolated grid:
> https://earth-info.nga.mil/GandG/update/index.php?action=home

Cool.
Looks like another way to compare geoid and ellipsoid heights.


After further reading at the weekend I got the impression that the whole
thing is a non-issue. The German vertical reference system DHHN92 [2]
uses a German Quasi Geoid which is "similar" to EGM96. The differences
between the geoids seem to be small (Couldn't find any numbers.). In
comparison to the vertical errors of NASADEM these differences are
probably negligible. So I would conclude, I do not need to transform the
NASADEM heights for using them in a model across Germany.

But I would still be interested in the differences of EGM96 and DHHN92.....



Many thanks for your interest
  Robert

[1]: https://en.wikipedia.org/wiki/World_Geodetic_System
[2]: https://de.wikipedia.org/wiki/Deutsches_Haupth%C3%B6hennetz#DHHN92
-------------- next part --------------
A non-text attachment was scrubbed...
Name: pEpkey.asc
Type: application/pgp-keys
Size: 2464 bytes
Desc: not available
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20200713/7f39dca5/attachment.key>