BRouter: Elevation algorithm

Elevation awareness is the most important issue in bike routing if not routing in a flat country. But in most routing software, elevation is either not handled at all or in a way that is not really useful.

Even worse, most tools do not even report on elevation in a useful manner. The far-too-high "total climbs" usually reported do not only accumulate real, small height-variations that are averaged-out by the bikers momentum - they accumulate also noise and grid-interpolation errors from the elevation data source.

BRouter uses elevation data from the Shuttle Radar Topography Mission (SRTM), precisely the hole-filled Version 4.1 Data provided by srtm.csi.cgiar.org, which is the data that is displayed e.g. in Google Earth and which is used in most elevation-enabled routing tools. However, the routing algorithm is able to extract the information on real ascends and descends and ignores the noise.

See the section about crossing the alpes for real examples.

On the reporting side, BRouter uses a similar concept to compute the "filtered ascend", which is the ascend without the noise and the small hills and which turned out to be a valid concept to estimate the real elevation penalty.