The waypoints are not distributed regularly, but the track points are.

Here is why performance mattered in my case.

I needed to predict future positions of the cyclist (see https://www.ibm.com/developerworks/community/blogs/jfp/entry...). The computation relied mostly on weather forecasts provided for each track points.

I then needed to know where to start my computation, i.e. find the track point closest to the current location of the cyclist.