So, there was quite a lot of work to do, but now the first prototypes show some progress! The latest version is able to record my tracks, which are colored by fuel consumption. The cool thing, when you start a new track, all recorded tracks in your area (map region) are loaded and visualized on the screen. Still there are lots of use cases left to solve, but milestone 1 (getting car specific consumption data and visualize it on a map) is done. Finally :)
By the way, getting more and more into it, the name of the project (and app) changed to….
Next milestone: store consumption tracks on a remote data base for community usage, appropriate eco value calculation, create first UI related ideas