Enable the use of offline maps

[sgelb]

As a user, I want the possibility to download map data in advance and disable the use of online maps. This would reduce the used bandwidth on the road and speed up the time until the map can be rendered.

OsmDroid supports the integration of MapsForge to render offline vector maps. The basic implementation is pretty easy, see here. I tried this on a local branch and it does work very well.

There are multiple sources available to download offline maps. It is also possible to reuse offline maps already downloaded e.g. for Locus or Oruxmaps.

Related to #265.

[saemy]

Sounds amazing! Mind sharing the progress in a WIP PR?
Related: Allow the integration of OsmAnd map files as they might already be around.

[sgelb]

Yes, I'll update my outdated proof of concept branch and push it in the next days as a WIP PR.

Integration of OsmAnd would be really great - it's my prefered map app -, but will not work. They use their own data format, the code is heavily integrated into OsmAnd and there is no lib.

[mulles]

With #274 done, I just tried the app on my FOSS only Phone. I am really happy to find likeminded people here :)
After testing the app the same ideas as here discussed came to my head:
-> Offline Maps
-> OSMand as source for vector maps (as already stored on my phone)

After little research before this post I can confirm @sgelb statement, OSMand
used different file format called .OBF. Maps can be generated as described here: https://wiki.openstreetmap.org/wiki/OsmAndMapCreator.

Another approach would be to import the WS hosts as POI's to OSMAND and open profile with a link within OSMand pointing to WSandroid App.
->An export WS as POI's would be needed from WSandroid

Any update on @sgelb your PR?