Ok, that is more work for me but possible to handle.
Thanks.
PS: perhaps I could write a little tool (based on xml data), that generates an "walkable corona" around my defined waypoint paths automatically...hm.... I love such small puzzles. PPS: Not, what I need, but very interesting:
http://www.geosensor.net/papers/duckham08.PR.pdf , PPPS: That is the right way:
click