implements https://github.com/valhalla/valhalla/pull/3318 to only download elevation tiles which are covering the graph tiles. this meant we had to switch to a build process in stages, where we first build the base graph, then download the elevation tiles based on that and finally run the other stages to enhance the graph.
reportedly that reduces the disk space for the full planet by approx a terabyte!
fixes #40
implements https://github.com/valhalla/valhalla/pull/3318 to only download elevation tiles which are covering the graph tiles. this meant we had to switch to a build process in stages, where we first build the base graph, then download the elevation tiles based on that and finally run the other stages to enhance the graph.
reportedly that reduces the disk space for the full planet by approx a terabyte!