Litchi Height Restriction

[Facherty]

I couldn't find a simple and modern Mavic Air answer to the conundrum below, despite a wide search.

Simply, I had made a Litchi mission to stay within 30m of the ground as the drone climbed and then descended a hill. After I hit the 'play' button and the mission was 100% transmitted to the aircraft, a red message appeared in Litchi saying, "Aircraft altitude too high", and the mission did not start. I assumed that I had made an error in the programme (perhaps had left off an "Above ground" checkbox in a waypoint?) but I couldn't find the problem, so I returned home and started again. New blank Litchi page, new mission, similar route... identical result: "Aircraft altitude too high".

The answer was simply to quit Litchi, start DJI Go 4, and change my maximum height. It was a (UK legal) 120m, but I had to set it to 230m, even though it never went more that 30m above the ground:

At its highest point, the drone was 187m above the start point, which itself was 30m in the air. Therefore the drone would be 187+30m above the ground - 217m. (I added another 13m for the sake of "roundness")

There have been other posts on this matter, but they seem to have started from different places.

As an aside, despite wonderful weather, the film from this mission was not great - somehow the Mavic Air seemed shakier than usual. The wind was not excessive, so I am wondering whether the rates of ascent/descent I was asking for had strained the performance capabilities of the little craft?

 

[brett8883]

I couldn't find a simple and modern Mavic Air answer to the conundrum below, despite a wide search.

Simply, I had made a Litchi mission to stay within 30m of the ground as the drone climbed and then descended a hill. After I hit the 'play' button and the mission was 100% transmitted to the aircraft, a red message appeared in Litchi saying, "Aircraft altitude too high", and the mission did not start. I assumed that I had made an error in the programme (perhaps had left off an "Above ground" checkbox in a waypoint?) but I couldn't find the problem, so I returned home and started again. New blank Litchi page, new mission, similar route... identical result: "Aircraft altitude too high".

The answer was simply to quit Litchi, start DJI Go 4, and change my maximum height. It was a (UK legal) 120m, but I had to set it to 230m, even though it never went more that 30m above the ground:
View attachment 75681
At its highest point, the drone was 187m above the start point, which itself was 30m in the air. Therefore the drone would be 187+30m above the ground - 217m. (I added another 13m for the sake of "roundness")

There have been other posts on this matter, but they seem to have started from different places.

As an aside, despite wonderful weather, the film from this mission was not great - somehow the Mavic Air seemed shakier than usual. The wind was not excessive, so I am wondering whether the rates of ascent/descent I was asking for had strained the performance capabilities of the little craft?

Because the drone always understands height as height above the home point.

All Litchi does is take the AGL input and converts that to a home point height for the waypoint. You can see in your picture at waypoint 13 that you have inputted an AgL height of 30m but in parenthesis it shows the height it is telling the drone for the home point which is 152.6m above the home point.

So therefore that homepoint would have violated the 120m height limit you had programmed into the drone and the drone didn’t accept the mission.

Simply the aircraft doesn’t understand above ground height it only understands above homepoint height.

As far as the shakiness it’s harder to diagnose but remember just because the wind is light where you are doesn’t mean it isn’t stronger even just a few meters above you so 200 meters above you in a hilly or mountainous terrain really all bets are off and the wind at your level is somewhat unrelated to the wind at such a great altitude difference.

 

[Facherty]

Brett - thanks: this confirms my observations.

Agreed on the wind as a possible source of interference, Certainly, the section at the highest points (waypoints 15-19) are not changing rapidly in height, yet there are still wobbles.

Not a big thing anyway - happy to get my drone back after my most ambitious Litchi project yet! For once Litchi's estimate was spot on - it said 13mins for the mission; it took 12m50s...

 

[JonasJr]

Did anyone had problems with those above mentioned height restrictions? If one WP is accidentally above the allowed height (due to topography), is it then Litchi software or is it the DJI drone which prevents the drone from starting?

 

[brett8883]

Did anyone had problems with those above mentioned height restrictions? If one WP is accidentally above the allowed height (due to topography), is it then Litchi software or is it the DJI drone which presents the drone from starting?

The height above the home point is what is restricted not the AGL height. The drone is what restricts the aircraft from flying not Litchi. Litchi will send the mission to the aircraft as you have entered it no matter what, it’s the aircraft that accepts or rejects.

 

[Facherty]

Agreed with brett8883. The solution is within the DJI Go 4 app - change your maximum height. This is explained in the first post in this thread.

 

[GregE]

Interesting clump of trees in center of the picture
and thanks for the info on planning routes

 

[JonasJr]

Agreed with brett8883. The solution is within the DJI Go 4 app - change your maximum height. This is explained in the first post in this thread.

Thank you for your helpful comments. Indeed, my setting in the DJI Go 4 app was probably responsible for not being allowed to lift off. The set maximimum height in the app was 4 m lower than the highest altitude of the waypoint above the *starting ground*. It is actually weird that the set maximum flying altitude in the app does not consider the changing topography as reference but the location of the starting point. If I would have planned my mission with a start right next to this highest WP (a hill top), than everything would be judged as legal. But in my case, flying upwards within the legal height limit is considered as illegal.