Baro alt vs GPS alt?

Fairly new to flying the Iris +.  Flights getting progressively bolder as I gain confidence.

Beautiful night last night and wanted to take video at sunset (didn't get it because somehow I switched GoPro out of video mode, oh well try that again later)

Any way I flew higher than I ever have in the past ~300' and the whole flight was perfect (not counting GoPro mistake) However as I was flying I looked at Telemetry on my Tx (Taranis) and saw a big difference between the 2 different altitude sensors. Entire flight in Loiter mode btw.

After landing I plugged in to Mission Planner to see what it said the altitude was since I'm not completely sure the Taranis is configured exactly right to properly show Telemetry data yet.  I saw the same mismatch of altitude data in MP.

This got me to wondering about which unit of measurement each is using, meters vs feet.  I looked through params and all through MP trying to find out how to specify which units to use and never saw it (I'm sure it's there, everything else is)

The GPS was showing ~ 3x the value the Barometer was so I think GPS is showing in feet and Baro in meters but I'd like to verify things and make sure both are outputting Telem data using the same units.

Also which sensor is the Pixhawk using for alt data if RTL is invoked?

Thanks,

Bob

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  • Perhaps helps if you share the log. didn't you have relative and abs altitudes in different readings? RTL uses basically baro, gps have much err in altitude, you can looks MPlanner units in config/tunning  page without connecting your Drone.

    • Ok thanks for the help, I missed RelAlt.

      Looking at the log again:

      Baro Alt = 115.65m

      Rel Alt   = 114.97m

      Closer than I expected, and a lot closer to my 120m Geo Fence than I wanted to get....

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