Improved elevation tile downloading in Python

[chrstnbwnkl]

Issue

fixes #3298 by replacing valhalla_build_elevation bash script with a corresponding Python script, which

• adds shapely support while still supporting the bbox method
• uses hyperthreading
• accepts a directory path as an argument that will be parsed for GeoJSON files
• handles Polygons and MultiPolygons

Tasklist

• Add tests
• Add #fixes with the issue number that this PR addresses
• Update the docs with any new request parameters or changes to behavior described
• Update the changelog
• If you made changes to the lua files, update the taginfo too.

Requirements / Relations

Waiting to merge #3308 so this can be properly tested

[nilsnolde]

we already had some rounds internally reviewing this. until final review I'd ideally like to merge #3308 before. anyone chiming in is appreciated!

[nilsnolde]

@chrstnbwnkl #3308 is merged, you can look there to see how testing works for these scripts: the most important part is that you relatively symlink the script you wanna test into the folder where the test file is with a .py extension, then you can import the script you wanna test easily

[nilsnolde]

I made the same mistake, see #3308 (comment)

you can leave it for now until we had a chance to discuss it in the PR meeting (to save some CI hours:))

[nilsnolde]

to leave it here as well: I just found a file which is not built anymore, https://github.com/valhalla/valhalla/blob/master/src/valhalla_tiles_for_elevation.cc. that actually outputs a list of the elevation tile "names" the graph covers. it seems to be forgotten about over the years and I think it doesn't need to be written in c++ as long as it's not actually lazy-loading at runtime as @kevinkreiser suggested but just a script producing output.

should we include that functionality in this PR and remove that file? I didn't think about it before but now that I see it it makes total sense. then we'd have 3 options for downloading elevation tiles: bbox, polygons and data-driven, all having their merit IMO.

[dnesbitt61]

I wrote that a couple years ago as a way of reducing the elevation data size by not downloading data over oceans and places where no roads exist. This reduced the size of worldwide elevation from ~1.5TB to ~500GB. It would be great to add this logic to valhalla_build_elevation as an option.

[nilsnolde]

I added the option to only download tiles the graph covers to valhalla_build_elevation and re-arranged a little but didn't change much more @chrstnbwnkl . was in a bit of a hurry, we want to use that feature for the fossgis server, so we only download 500 gigs.

should be ready for review. CI will fail, we first need the docker image with python3-shapely installed. I'll PR real quick