@rmackay9
I would like to suggest the possibility to include Radar (Rangefinder) information for RTL as a sensor option. I´m having serious problems on low flying crop sprayer operations, since many times you take of at a certain altitude (marked as zero on the barometer) and you spray down the hill. The usual flight is 3 to 5m above the crop height, adjusted by Radar (not barometer). When the RTL triggers, having for example a 10m RTL_ALT (1000), the copter can be at a lower altitude at this moment, for example minus (-)15m at the Baro reading. Now he will crash into the ground before returning home since the Radar info is ignored.