GLOBE Elevation data alternate download

[albar965 1,040]

I added an alternate download location in the LNM download section: https://www.littlenavmap.org/downloads/GLOBE Elevation Data/

Just in case the download page https://ngdc.noaa.gov/mgg/topo/globe.html is not available.

 

Alex

[rusentu 0]

Hi Alex.
Your program is very useful and simple.
I installed global elevation files the other day.
https://www.littlenavmap.org/manuals/littlenavmap/release/2.6/en/OPTIONS.html#install-globe-elevation-data
I haven't noticed much difference from online.
I also noticed that everyone downloads from the site:
https://ngdc.noaa.gov/mgg/topo/gltiles.html
The archive is very old there.
2004 year...

How can you use data from these services?
https://lpdaac.usgs.gov/products/astgtmv003/
https://earthexplorer.usgs.gov/
https://earthdata.nasa.gov/
http://dwtkns.com/srtm/
Which DEM file format does Little Nav Map accept?
https://ngdc.noaa.gov/mgg/topo/report/globedocumentationmanual.pdf

Edited October 30, 2021 by rusentu

[albar965 1,040]

3 hours ago, rusentu said:

The archive is very old there.

I know.😞 
On the one hand, the mountains rearely change🙃, on the other hand, the data is a bit too low-resolution.

Therefore, I'm looking into alternatives.

Plenty thanks for the links. I added them to this issue: https://github.com/albar965/littlenavmap/issues/282
No idea when this will happen. I need a free to use dataset which is not too big and uses simple format.

Alex

[rusentu 0]

To understand, are you using data from the GLOBE files and plugging it into the altitude profile of the flight plan (red arrows in the figure)?
Flight plan exceedance profile - green bar at the bottom of the program?
What data format have you set for use in LNM?
GLOBO?
When we select online in the LNM program - is the data also taken from the server https://ngdc.noaa.gov/mgg/topo/gltiles.html?
After a bit of research, there are now many other height formats:
GTOPO
ETOPO
GMTED2010 (It seems suitable to me that this format is most for replacing GLOBE):

https://topotools.cr.usgs.gov/gmted_viewer/gmted2010_global_grids.php(ZIP)
https://pubs.usgs.gov/of/2011/1073/pdf/of2011-1073.pdf
https://topotools.cr.usgs.gov/gmted_viewer/viewer.htm
https://yceo.yale.edu/gmted2010-global-multi-resolution-terrain-elevation-data
Data in Russian(please use google translator) - https://desktop.arcgis.com/ru/arcmap/latest/manage-data/raster-and-images/wkflw-elevation-part1.htm
In the section - public data, many links to open data.
To fully understand elevation data, it is also necessary to distinguish between absolute (relative to the geoid) and geodetic (relative to the ellipsoid) heights.
Geodetic heights are the heights of points above or below an idealized surface when the shape of the Earth is assumed to be an ellipsoid.

I downloaded this archive, about 600 megabytes.
I opened it with the help of the program QGIS and received data on the heights of the earth.
https://edcintl.cr.usgs.gov/downloads/sciweb1/shared/topo/downloads/GMTED/Grid_ZipFiles/sd15_grd.zip

Edited October 31, 2021 by rusentu

[albar965 1,040]

30 minutes ago, rusentu said:

To understand, are you using data from the GLOBE files and plugging it into the altitude profile of the flight plan (red arrows in the figure)?
Flight plan exceedance profile - green bar at the bottom of the program?

Yes.

30 minutes ago, rusentu said:

What data format have you set for use in LNM?

None. I read the GLOBE files directly. They can be accessed on the fly while hovering the mouse above the map. The code is replaceable (one C++ class) which allows to change the format without messing up the whole program.

31 minutes ago, rusentu said:

When we select online in the LNM program - is the data also taken from the server https://ngdc.noaa.gov/mgg/topo/gltiles.html?

No. It uses the default source https://maps.kde.org/earth/srtm2/ (see file srtm2.dgml in LNM installation). This data has a lot of issues and very limited coverage. 

35 minutes ago, rusentu said:

To fully understand elevation data, it is also necessary to distinguish between absolute (relative to the geoid) and geodetic (relative to the ellipsoid) heights.
Geodetic heights are the heights of points above or below an idealized surface when the shape of the Earth is assumed to be an ellipsoid.

Ellipsoid (i.e. WGS84) is not used in in LNM (and the Marble widget) or in aviation in general. Earth is assumed to be a sphere for simplicity. Ellipsoids would make distance calculations insanely complex. Yes, some of the datasets would need an additional conversion step from ellipsoidal height to spherical height.

Thank you for the links. I added them to the Github issue.

If you or anybody can program C++: Feel free to help out.

Alex