Need to create auto mission which at each waypoint descends to height x AGL (with sensor)

I am working on a copter application where it is essential to fly to a set of waypoints and descend at each point to a certain height to perform a task before moving on to the next waypoint, then descend there again, and so forth.

The height descended to at a given coordinate/ waypoint must always be the same - say 0.7m above actual terrain.
(The terrain is not flat, therefore I will need to use a rangefinder sensor)

I have researched this and found absolute waypoint heights and relative to home waypoint heights. Also terrain following based on geotiff. But I have not found how to set waypoint to use a rangefinder input to always descend to 0.7 m.
The terrain is unknown, and there are no maps available accurate enough to be reliable. So the input that needs to be “trusted” there is the rangefinder reading.

Can anybody point me to a solution? Any help is greatly appreciated as the entire application heavily depends on this flight pattern/ procedure working.

If you use APM Planner 2.0 you can set the frame (ABS, Relative, Terrain (i.e. AGL based on RangeFinder) per waypoint.

I also have working branch to add that feature to Tower.

The solution would be to set three waypoints at the target location. One for arrival, one to descend to the 0.7m alt, and one to return to starting alt.

Thanks for the hint, Bill. I had the same approach in mind, with the three WP stacked on top of each other.

I have never used APM Planner yet, so the thought of using an alternate GCS is new to me. But that would require running matching firmware, no? I am a little shy of the additional learning curve, though… (Or am I maybe missing the obvious here and APM Planner will happily interface with the same Copter-3.4 firmware as Mission Planner does?)

Ideally though - does anybody know if the needed functionality is possible with Mission Planner (and the matching firmware) as well?

APM Planner 2.0 is AC3.4 compatible, it detects it automagically.

MP is either terrain or abs/relative I don’t think you can mix missions

mission planner only supports a single mission frame per mission.

Thank you for the inputs.

@billb Good to know that 3.4 would run on APM Planner. But it seems like RTK is not supported - yet this accuracy is essential to the application I have in mind…
Would it be possible to upload a flight plan with waypoints based on terrain heights (and supported by a rangefinder) using APM Planner - yet then carry out the actual auto mission with Mission Planner to get any RTK benefits? Or am I completely messing up compatibility concepts here?

"Single mission frame", I take it, means that what Bill has outlined: Either terrain based or abs/relative - correct?

If I then made the missions generally terrain-based (in Mission Planner), but vary the terrain-based AGL height at the waypoints where I need it - is this a feasible workaround?
(Sorry if questions seem weird - can’t test it yet by upload/ download of flightplan myself (am waiting for Pixhawk2 to be delivered), but am also trying to move forward with project and identify potential “show stoppers”.)

Hi Michael,

Any specific reason why Mission Planner only supports a single frame per mission? Would you consider supporting multiple frames in the future?

That’s a good question. Would supporting multiple frames be possible in Mission Planner? Or does the underlying architecture maybe not allow this?

the reason is that why you may want this, I think 90% of the population will only end up confused. and result in a crash because of a badly programmed mission.

Thanks for the feedback, Michael.
If the concern is only to avoid a possible, accidental mishap, I think that situation could easily be avoided by a general switch in the settings.

That way the default would be as you see fit, yet the option to fly to waypoints based on terrain height and accomplish measurements or other work at a constant height could still be available - without the risk you foresee.

There is a currently thread “Enhancement - Copter - create mission for vertical mapping” which also has a need for a consistent distance of a waypoint away from an object:
"…it would be great to also include an ability to set a horizontal stand off distance from an object that may be sensed by a LIDAR or any other type of range sensor."

If I understand correctly, this type of vertical mapping/ inspection of vertical structures would then have a somewhat similar requirement as my suggested enhancement - a predefined distance to an object…

If one thinks of planning and automating missions of, say

  • hi-res optical inspections of large, slanted roofs or
  • other 3D-objects/ shapes/ structures or
  • photo voltaic installations on a hill side or
  • other scientific measuring at a given distance from the ground (while terrain-following) or
  • identifying land-mines more accurately,

this need for flying way points at a constant distance based on range-finding (rather than only an absolute or relative-to-home height) comes into play again and again.

So having the (hidden?) option to program more complex way points based on sensed terrain heights has a number of valid applications and would really be a helpful addition I believe.