I sometimes get high GPS_HDOP values (i.e. above 2) so naturally my copter (3DR X8+) fails the pre-arm check. However, once the copter goes up a few meters, I imagine the signal will get better in most instances. So I was wondering if it’s possible to take the HDOP off the pre-arm check and making it a failsafe, so once the copter reaches its flying altitude it checks the hdop and if it’s too low it does an RTL. So in effect making the hdop kinda like a geofence. Or maybe program the copter to have one HDOP value when it’s on the ground (e.g. 350) and another when it reaches it’s first waypoint up in the air (e.g. 200).
Thanks
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Thanks, I hadn't considered the scaling of position errors. In my (somewhat limited) experience adding GLONASS doesn't help all that much. Having more satellites doesn't help much if you are in a narrow valley or if you are surrounding by lots of trees.
Waiting longer to take off does give the GPS 15 minutes to catch up with the almanac.