Thats a good point and I really do want to integrate HDOP in the rerouting-check calculation. But as there might be another causes for false-alerts, namely routes that were mapped with a slight offset or routes that were mapped correctly, but then reduced in point count to reduce storage space (eq. you might get a straight line for a slightly curved route in the routing result), I would still like to let the user to set the rerouting distance to some arbitrary number manually, to get rid of excessive reroutes in some cases. IMHO, just using a HDOP multiple won't work - if you have a very good HDOP (say <1 m), the real route differing just 3 meters from the computed one would trigger rerouting. A very bad HDOP (>100m) would result in a 300+ m corridor. ... Possible algorithms that take HDOP into account: Algorithm nr. 1 ... Algorithm nr. 2 ... Algorithm nr. 3: ... Algorithm nr. 4:check if HDOP < (1/3)*rerouting_threshold (in meters) if its larger, them rerouting threshold = 3*HDOP