Per default elevation is disabled. But you can easily enable it e.g. via
graph.elevation.provider: cgiar. Or use other possibilities srtm, gmted
or multi (combined cgiar and gmted).
Then GraphHopper will automatically download the necessary data for the area and include elevation for all vehicles - making also the distances a bit more precise.
The default cache directory /tmp/<provider name> will be used. For large areas it is highly recommended to
use a SSD disc, thus you need to specify the cache directory:
graph.elevation.cache_dir: /myssd/ele_cache/
The average_slope and max_slope attributes of a road segment can be used to make your routing
elevation-aware, i.e. to prefer or avoid, to speed up or slow down your vehicle based on the elevation
change. See the custom model feature.
All should work automatically but you can tune certain settings like the location where the files are
downloaded and e.g. if the servers are not reachable, then you set:
graph.elevation.base_url
For CGIAR the default URL is http://srtm.csi.cgiar.org/SRT-ZIP/SRTM_V41/SRTM_Data_GeoTiff/
and this is only accessibly if you specify the full zip file.
If the geographical area is small and you need a faster import you can change the default MMAP setting to:
graph.elevation.dataaccess: RAM_STORE
The CGIAR data is preferred because of the quality but is in general not public domain. But we got a license for our and our users' usage: https://graphhopper.com/public/license/CGIAR.txt
Using SRTM instead CGIAR has the minor advantage of a faster download, especially for smaller areas.
Integrating your own elevation data is easy and just requires you to implement the ElevationProvider interface and then specify it via GraphHopper.setElevationProvider. Have a look in the existing implementations for a simple overview of caching and DataAccess usage.