Custom elevation data

stefcud · April 22, 2020, 6:40pm

hi

I would like to use my custom data in place of the classic srtm / cgiar, I have available geo-referenced geotif(.TIF) files in the right way that cover my road graph

how can i use them? do I have to put them in a zip file that has the same name as my elevation cache automatically downloaded?
in my case only one file: srtm_39_03.zip
contains: srtm_39_03.tif,srtm_39_03.hdr,srtm_39_03.tfw

changing the elevation cache the graph cache should not be regenerated right?

Could it be an interesting feature support to custom elevation provider

nils · April 23, 2020, 6:17am

just try it and let us know. We have no experience at all using different elevation providers. I’d figure that you need to use the same name as the tile would have for cgiar. Also of course the same CRS. Other than that it might just work, a tif is a tif…

And no: graph rebuild is required when changing elevation files.

HendrikLeuschner · April 23, 2020, 9:57am

Check out Graphhopper:

github.com

graphhopper/graphhopper/blob/master/docs/core/elevation.md

# Elevation

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/`

## What to download and where to store it? 

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 there are two URLs you can use: `http://droppr.org/srtm/v4.1/6_5x5_TIFs` and

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nils · April 23, 2020, 10:04am

Yep, for in-code solutions. I’d guess you can hack it though if you pretend to have CGIAR by putting it into the elevation_cache folder and giving the file the same name it’d have had with CGIAR. Obviously has its limitations, e.g. not sure what happens if multiple own tiles overlap with a cgiar tile.

Anyways @stefcud, should be even easy to infer from the GH code what’s possible and what not without touching the code. Else good old trial & error.