Coordinate Frames in QGC

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Coordinate Frames in QGC

Postby nplayle » Sat Jul 19, 2014 7:41 pm

Hi all,

I'm working on getting some autonomous flights done but I've got some questions about QGC, specifically about the coordinate frames used in the waypoint setup menu.

1. I would like to specify waypoints in terms of positions and altitude relative to takeoff. Eg, fly (10, 20, 5) will fly to a point 10m north, 20m east and 5m above initial takeoff points.
1a. Currently it looks like the 'local' frame would do this, however it says 'Z negative', but then has D 550m (for example). I'm assuming this is 550m 'down', which is 550m ASL correct? How do i specify absolute altitude above initialisation point? I don't like the idea of relative altitudes because on larger missions you end up having to take a running tally of your altitude movements. Specifying absolute altitudes ASL is annoying as well because to fly the same mission in multiple locations you need to update the height, lest it fly into the ground or off into the sky.

1b. It also looks like the 'mission' frame might be able to do this as well. Are these implemented / which one to use?

2. Are the takeoff, rth and land commands working correctly as of 6.7.r224.b1400?

Thanks,
Nick
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Re: Coordinate Frames in QGC

Postby Max » Sat Jul 19, 2014 7:45 pm

Hi Nick,

1) To specify relative alt., use the Global/Rel. Alt. option. Only the Global frame types work with AQ.
2) Yes, as far as I know...

-Max
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Re: Coordinate Frames in QGC

Postby nplayle » Sat Jul 19, 2014 8:12 pm

Hi Max,

Thanks for the quick reply, going to test it later this afternoon.

Do you know if there are any plans to add relative waypoint navigation?

Nick
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Re: Coordinate Frames in QGC

Postby Max » Sat Jul 19, 2014 8:33 pm

Do you mean X/Y coordinates relative to previous waypoint? Eg. "go 10m at heading 270." No plans that I know of, although I can see how that could be useful. Not sure if this would be better as a GCS (mission planner) function, or implemented onboard the aircraft. Both ways could work...

Cheers,
-Max
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Re: Coordinate Frames in QGC

Postby nplayle » Tue Jul 22, 2014 5:02 pm

It could work on either the GCS / aircraft side, but I think aircraft side implementation would be safer. That way the aircraft always stores relative waypoints rather than absolute-waypoints-converted-from-relative if they are ever stored to flash. Plus I think to do it from the GCS side you'd have to have the known starting coordinates which breaks some of the reusability (eg, flying a square at flying site A uses a different waypoint file than flying the same square at flying site B)

I believe the Pixhawk uses something along the lines as 0,0 is the intialisation point, and you have commands such as

fly(10,15)
fly(20,10)

Goes 10m north and 15m east from the start point, and then go to 20m north and 10m east of the start point (typically point of first GPS lock). Negative numbers specify distance south and west.

As an example, in APM (http://copter.ardupilot.com/wiki/planni ... nd-events/) you have a waypoint bitmask that can specify if the waypoint is abolute in world coordinates or relative to the initialisation point (bit 4).

Nick

P.S. Got my hex flying over the weekend and its looking good, navigates and lands okay but on takeoff it seems to sit and think for about 15s before flipping itself over. Haven't looked at the logs yet but I suspect my throttle probably isnt in the right place and its getting wound up.
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