Altitudes in APM 2.68

Hi all,

I'm flying an APM2.5 with version 2.68 of the code. I'm having an issue with altitude.

I boot up the auto pilot and wait for it to get GPS lock. Often times, the altitude says around 20m or so. My altitude above mean see level (which I think is what GPS uses) is about 20m so this could be correct. I then hit the "zero home altitude" button on the mission planner and my altitude does indeed move to 0. The problem is that when I go to fly in auto, the desired altitude of each waypoint is not what I've set it to in my mission. Often times I set all my waypoints to 80m. Instead of flying around at 80m, the autopilot will fly around at another altitude like 60m (The fact that 80-20=60 doesn't seem to be just a coincidence!). And it's not as though the autopilot is trying to get to 80m; it's desired altitude is indeed 60m. If I don't zero out the altitude when I boot up the APM, then the mission will indeed be executed at the correct indicated altitude (80m), but it wont be 80m with respect to the ground. It will be 80m with respect to whatever altitude it started up with (most times around 20m).

Has anyone else noticed this behavior?

Anyone know how the altitude is supposed to be handled? It seems to me that if you enter waypoint altitudes and you don't have the abs altitude button checked, then the desired altitude should be relative to what you started out as. And in the case of zeroing out the altitude while on the ground, then I can't see why it wouldn't fly at exactly the desired altitude of each waypoint...

Any help would be appreciated.

Also, I do not have absolute altitude checked in the flight planning tab.


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  • Where is the "zero home altitude" button in mission planner ?




  • So it safe to use the plane in all modes except maybe AUTO without bringing the computer to the field? I dont really like to always set altitude to zero and bring my PC and based on what Will says i dont have to?



  • I have the same issue i think.
    Will do some more testing, maybe its just mission planner messing things up.

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