Digital Elevation Model get more accessible and open-source. It's pretty "easy" to produce elevation contours using a software like QGIS. It would be great to be able to import contour file to produce a pseudo DEM in CRP.
I have attached a KML format export file as an exemple if you want to have a look and see what could be done. There are many other formats available.[[File:contours_test_2.kml.zip]]

I believe WGS84 is standard to kml format and whatever coordinates datum is used, QGIS will converted them during the export to kml... I created another set of isohypses using GML format with UTM 31 coordinates. File attached below.

I assume you've already downloaded one or several DEM raster tiles and you know their original Coordinates Reference System (CRS).

Two sources of free/global DEM
NASA SRTM: https://earthexplorer.usgs.gov/
ALOS AW3D30: https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm

In QGIS:

Set the project Coordinates Reference System (CRS):
1 - Top menu bar: Projet > Properties > CRS > Select the appropriate UTM CRS.

Import DEM tiles into project:
2 - Top menu bar: Layer > add layer > add raster layer >> select raster dataset(s) > Open.
3 - Set DEM tiles' CRS: in Layers panel: right clic on each tile > Layers CRS > Select the appropriate original DEM CRS (potentially different from UTM)

If several adjacent tiles, create one Virtual Raster:
4 - top menu bar > Raster > Miscellaneous > Build Virtual Raster >> Select input tiles, Resolution "High", untick "place each input file into separate band", in "Virtual": save to file > Run.
5 - Set DEM virtual tiles' CRS: in Layers panel: right clic on virtual tile > Layers CRS > Select the appropriate original DEM CRS (potentially different from UTM)

Create contours from DEM tile or from virtual DEM tile:
6 - top menu bar: Raster > Extraction > Contours >> select input layer, define interval between contour lines, save to file > Run.
7 - Set DEM contours layer's CRS: in Layers panel: right clic on contours layer > Layers CRS > Select the appropriate contours CRS (should be the same as original DEM)

Export contours to GML:
8 - in layer panels: right click on contours layer > Export > Save features as >> select Format = GML, set file name, set layer name, select export CRS: should be the appropriate UTM CRS > OK.

Done.

Hi Jochen,

That's a massive area and 7.5 arcsec resolution isn't great. In many countries, national DEM have become open-source, and they often have a high resolution and accuracy. You just need to know where to find them... If not, NASA SRTM (available on https://earthexplorer.usgs.gov/ in Dataset > Digital Elevation (where you found GMTED2010) > SRTM) and ALOS AW3D30 are a good source of free and global DEM. They both have a 30-metre resolution. AW3D30 claims a vertical accuracy of 5m, SRTM claims an absolute accuracy of 16m and relative accuracy of 6m (from pixel to neighboring pixels).

I had a look at the DEM available in your area: SRTM has unfortunately many voids (missing pixels/data) in your expedition area and won't be of much use. Luckily, the ALOS AW3D30 seems of a much better quality in this area : https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm. I believe you need to create an account first. For your expedition area, you can download the following corresponding tile here: https://www.eorc.jaxa.jp/ALOS/en/aw3d30/...45E010_N047E012

1 - From the package, open the *DSM.tif file in QGIS.
2 - Make sure the CRS is WGS84 (EPSG4326).
3 - Create the contours for the entire area. In Top menu: Raster>Extraction>contours >> Select input layer (DEM), set the required interval >Run

That remains lots of data and a huge area, so you need to extract from the contours created the contours for your expedition area.

4 - In top menu: Layer >Create Layer> New Shapefile Layer >> give the new layer a name, select Geometry type = polygon > OK
5 - In Layers Panel: Right clic on the newly created layer > Toggle Editing. This layer is now editable.
6 - In top menu: Edit> Add Polygon feature. Start drawing the polygon of your expedition area. When done right clic>> OK
7 - In top menu: Vector > Geoprocessing Tools>Clip...>> Input layer is the contour layer, Overlay layer is your expedition area > Run
8 - In Layers Panel: Right clic on the clipped contours layer>Export>Save feature as >> Format GML, give the file a name, select the export UTM CRS >> OK

Done!! :)

Prima!

The results is really impressive! Thank a lot!

Hi Jochen,

Would it be possible to display the contours in Plan mode?

My user story... I'd like to be able to overlay surface contours with the cave, to highlight the relation between surface and cave(s) in plan mode: proximity with the surface or crossing through a mountain, valley and riverbeds... as well as the topographic relief for cave access.
Ideally it should be exportable as a drawing layer (like we can with surevy shoots).