Litchi and waypoint heights

[analbeard]

I've had Litchi for a while but not yet had the courage to hand control of the drone over to it. After browsing this subforum I read about VLM, so I imported a mission into it but the heights are all over the place. I'm flying around a ridgeline so the ground height varies - the mission starts off 100ft above the ground and stays there up the side of the hill (first three waypoints have 'above ground' ticked). I then set the remainder to an absolute height which is the ground height of the third waypoint + 100ft.When I open this in Google Earth the track starts off as I expect but at the third waypoint it shoots up another 1050ft, even though 'above ground' isn't ticked.

Which do I trust? Litchi hub or Google earth?

 

[Kazzaaz]

Honestly I wouldn't fly the route if Google Earth isn't matching up with Litchi.
The data Litchi uses for ground altitude isn't 100% reliable in my experience.
I get the altitude profile using a path on Google Earth and then work in absolute altitudes on Litchi using GE as reference.
Of course, the best way to get your altitudes is to fly there and measure it yourself while in LOS!

 

[brett8883]

I've had Litchi for a while but not yet had the courage to hand control of the drone over to it. After browsing this subforum I read about VLM, so I imported a mission into it but the heights are all over the place. I'm flying around a ridgeline so the ground height varies - the mission starts off 100ft above the ground and stays there up the side of the hill (first three waypoints have 'above ground' ticked). I then set the remainder to an absolute height which is the ground height of the third waypoint + 100ft.When I open this in Google Earth the track starts off as I expect but at the third waypoint it shoots up another 1050ft, even though 'above ground' isn't ticked.

Which do I trust? Litchi hub or Google earth?

I didn’t think Litchi could do a relative to the pervious height reference. If you don’t have AGL checked it’s just going to be relative to your home point. Did you defend down from the home point in this mission?

 

[analbeard]

Right, I think I sussed my problem - I didn't properly understand how the heights were calculated relative to the first waypoint. I think I've also introduced some confusion by the fact that I'm starting the mission already in the air as opposed to allowing to take off etc. I've now got the track in Google Earth nice and flat so I think I'm a bit more confident with it. I'll try it out this weekend and just be read to kill it if needs be.

 

[br-travel]

I have a related question, I want to fly the exact same path, but from two different takeoff points which are about 50ft different in elevation. How should I do this in Litchi hub? Are the elevations I set in the hub always relative to the takeoff point elevation? Or if you check the box, it's relative to ground elevation supplied by Google Earth?

If that's the case, it seems I have two options. (1) Find the exact elevation difference of the takeoff points, let's say 53ft, then the mission taking off from the lower elevation will use waypoints at 100ft, and the mission taking off from the higher elevation will use waypoints at 47ft. or (2) Check the 'above ground' box, and use the same waypoint elevations for both missions.

Does that sound right?

 

[sar104]

I have a related question, I want to fly the exact same path, but from two different takeoff points which are about 50ft different in elevation. How should I do this in Litchi hub? Are the elevations I set in the hub always relative to the takeoff point elevation? Or if you check the box, it's relative to ground elevation supplied by Google Earth?

If that's the case, it seems I have two options. (1) Find the exact elevation difference of the takeoff points, let's say 53ft, then the mission taking off from the lower elevation will use waypoints at 100ft, and the mission taking off from the higher elevation will use waypoints at 47ft. or (2) Check the 'above ground' box, and use the same waypoint elevations for both missions.

Does that sound right?

You have identified a real problem, but there is a simpler solution to it. Litchi uses "relative to ground" elevations perfectly well to create mission profiles but the aircraft only knows about height relative to the takeoff point, and it doesn't know the elevation of the takeoff point. As a result, in anywhere other than perfectly flat terrain, you need to put the first waypoint directly over the takeoff point. That way it will correctly fly to the requested height AGL and all subsequent waypoints will be appropriately referenced.

If you need to fly a mission from various locations, or don't know exactly where you will start when originally planning it, then rather than trying to change all the waypoints, just include a spare, moveable waypoint at the start of the mission profile. After uploading it to your mobile device you can drag it to the correct location on the map when you decide where to launch from.