After fixing a problem, that the ground shape was not accurate enough represent by the physic collision, I decided that for the ground shape there will be a triangle accurate collision test.
This leaded to the idea of different grounds, which can now be easily added.
For my weekly update a added new screenshots, showing a new environment (mountain).
Its still under development - no background image, not the final shape of the mountain.
But I like the idea of having different levels with different ground shapes (also thinking about a Canyon, where you need to build something between a bridge and a building).