Waypoint Mission (IMPOSSIBLE) !!!!! 🇦🇮🦘

[Squidinc]

Hi all,

This is a "heads up" to be cautious when flying a preplanned waypoint mission, as altitudes can change from what you originally set!

Page 41 of the Air 3 manual states - "THE FLIGHT ROUTE WILL CURVE BETWEEN WAYPOINTS, SO THE AIRCRAFT ALTITUDE BETWEEN WAYPOINTS MAY BECOME LOWER THAN THE ALTITUDES OF THE WAYPOINTS DURING THE FLIGHT. MAKE SURE TO AVOID ANY OBSTACLES BELOW WHEN SETTING A WAYPOINT"

Recently I almost lost my Air 3 into the ocean because of this. This was due to a negative altitude being implemented by the waypoint flight that was not known until actually flying the mission. @KenG has had a similar issue, with DJI confirming that a new core board module was needed for his Air 3 and are replacing it under warranty.

Here is a short fun video of what happened in my case utilising my AirData stats. You can see how I was climbing nicely until suddenly at waypoint F a negative altitude is applied. In a state of panic I hit RTH with a second to spare. Enjoy!

Waypoints Mission (Impossible)-4K.mov

@Droning on and on...

 

[MARK (LI)]

Looks like quick thinking saved you....good thing you were paying attention

 

[DoomMeister]

This sounds like DJI is using a Curved Cable Camera with their waypoint missions. Each waypoint will be passed through, but the flight path will be a curve through those points to achieve smooth cinematic flight and video.

Other manufacturers have used this same approach and flight planning must allow for this. Also remember to factor in flight speed. The faster the speed the more the curves will deviate between waypoints.

 

[DJ Wes]

This sounds like DJI is using a Curved Cable Camera with their waypoint missions. Each waypoint will be passed through, but the flight path will be a curve through those points to achieve smooth cinematic flight and video.

This is correct. DJI uses a Catmul-Rom spline to define the flight path from the waypoints.

Also remember to factor in flight speed. The faster the speed the more the curves will deviate between waypoints.

Speed has nothing to do with the path. Geometry alone defines the path.

 

[MS Coast]

This is correct. DJI uses a Catmul-Rom spline to define the flight path from the waypoints.


Speed has nothing to do with the path. Geometry alone defines the path.

And the curved flight path happens in all three dimensions, not just two.

I had assumed that altitude would be controlled to the set values. I created a simple waypoint flight that involved moving to two locations at 200' AGL and descending vertically to 50'. The flight path was a smooth curve downward between the waypoints, which could have been a serious problem if there were obstacles between the waypoints.

 

[Pinedar]

Thanks for sharing! Did the altitude change after the mission began? How did RTH initiate?

 

[DoomMeister]

This is correct. DJI uses a Catmul-Rom spline to define the flight path from the waypoints.
View attachment 174957

Speed has nothing to do with the path. Geometry alone defines the path.

Thanks for the information update. Good to know speed does not affect the curves.

 

[4006448]

Love the music! Perhaps Mission Impossible required a submersible shore landing? Glad it worked out well with your quick action. Trust an Aussie to find the device’s limits.

 

[Shuttersky597]

Hi all,

This is a "heads up" to be cautious when flying a preplanned waypoint mission, as altitudes can change from what you originally set!

Page 41 of the Air 3 manual states - "THE FLIGHT ROUTE WILL CURVE BETWEEN WAYPOINTS, SO THE AIRCRAFT ALTITUDE BETWEEN WAYPOINTS MAY BECOME LOWER THAN THE ALTITUDES OF THE WAYPOINTS DURING THE FLIGHT. MAKE SURE TO AVOID ANY OBSTACLES BELOW WHEN SETTING A WAYPOINT"

Recently I almost lost my Air 3 into the ocean because of this. This was due to a negative altitude being implemented by the waypoint flight that was not known until actually flying the mission. @KenG has had a similar issue, with DJI confirming that a new core board module was needed for his Air 3 and are replacing it under warranty.

Here is a short fun video of what happened in my case utilising my AirData stats. You can see how I was climbing nicely until suddenly at waypoint F a negative altitude is applied. In a state of panic I hit RTH with a second to spare. Enjoy!

Waypoints Mission (Impossible)-4K.mov

@Droning on and on...

I have actually experienced this with my Mavic 3 classic, Specta Air, and my new Air 3. Waypoints have suspended when the point was set at 15 ft and during run it descended to 6. Three different drones , same thing.

 

[Squidinc]

Thanks for sharing! Did the altitude change after the mission began? How did RTH initiate?

Not sure when exactly the waypoint flight altitude changed. The sticks do not respond when flying a waypoint flight, so in my panic I hit the RTH button as a last resort. It worked….. Whew!

 

[Shuttersky597]

DJI knew exactly what to do with the pause/ RTH button.

 

[Kiwicbrthou]

Well that’s about as close as you’d ever want to get!
Just goes to show you can’t afford to get too distracted by stuff going on around you.

 

[mihaildorian]

Hi all,

This is a "heads up" to be cautious when flying a preplanned waypoint mission, as altitudes can change from what you originally set!

Page 41 of the Air 3 manual states - "THE FLIGHT ROUTE WILL CURVE BETWEEN WAYPOINTS, SO THE AIRCRAFT ALTITUDE BETWEEN WAYPOINTS MAY BECOME LOWER THAN THE ALTITUDES OF THE WAYPOINTS DURING THE FLIGHT. MAKE SURE TO AVOID ANY OBSTACLES BELOW WHEN SETTING A WAYPOINT"

Recently I almost lost my Air 3 into the ocean because of this. This was due to a negative altitude being implemented by the waypoint flight that was not known until actually flying the mission. @KenG has had a similar issue, with DJI confirming that a new core board module was needed for his Air 3 and are replacing it under warranty.

Here is a short fun video of what happened in my case utilising my AirData stats. You can see how I was climbing nicely until suddenly at waypoint F a negative altitude is applied. In a state of panic I hit RTH with a second to spare. Enjoy!

Waypoints Mission (Impossible)-4K.mov

@Droning on and on...

I also did missions but with the Mavic 3. Nothing special happened. Maybe you made a mistake somewhere or it was a system error.

 

[Squidinc]

I also did missions but with the Mavic 3. Nothing special happened. Maybe you made a mistake somewhere or it was a system error.

I definitely did not make a mistake as all the waypoints set were several meters AGL.

 

[Droning on and on...]

And the curved flight path happens in all three dimensions, not just two.

I had assumed that altitude would be controlled to the set values. I created a simple waypoint flight that involved moving to two locations at 200' AGL and descending vertically to 50'. The flight path was a smooth curve downward between the waypoints, which could have been a serious problem if there were obstacles between the waypoints.

This is very troubling, and makes planning a waypoint mission potentially much more difficult.

Is there some way to see the path in 3D and rotate it around?

 

[Squidinc]

This is very troubling, and makes planning a waypoint mission potentially much more difficult.

Is there some way to see the path in 3D and rotate it around?

I don’t believe so. DJI are aware of this. Personally, I’m not game to plot a waypoint flight now after my near fatal experience thanks to waypoint altitudes changing as the flight is in motion!

 

[DJ Wes]

Maybe you made a mistake somewhere or it was a system error.

This was not the result of a mistake or error. Instead, it is the result of a waypoint mission whose path is defined by a spline that passes through the waypoints and the waypoints were positioned such that the path between them is forced to be at a lower altitude than the waypoints on either side as shown by the red line in the image below.

This is very troubling, and makes planning a waypoint mission potentially much more difficult.

Is there some way to see the path in 3D and rotate it around?

One just has to be aware that the flight path exists in 3D space. In the image above and a spline that goes through the waypoints, there is no choice but for the spline to pass outside of the convex hull defined by the waypoints.

thanks to waypoint altitudes changing as the flight is in motion!

It's not that the height of the waypoints is changing. It is caused by the spline that passes through those waypoints and passing below a line that connects the waypoints.

 

[Droning on and on...]

It's not that the height of the waypoints is changing. It is caused by the spline that passes through those waypoints and passing below a line that connects the waypoints.

That's the explanation, but it's not an excuse for this behavior.

Lazy programming. There's no reason the curve has to be fit in 3D. The curve can be computed in 2D, and altitude transitions can be linear. This is pretty much what people expect, I believe. It's certainly what I expect.

I consider the aircraft following a vertical flight path I can't see on the screen during planning, nor can reasonably predict to be a serious limitation of the feature.

 

[Squidinc]

That's the explanation, but it's not an excuse for this behavior.

Lazy programming. There's no reason the curve has to be fit in 3D. The curve can be computed in 2D, and altitude transitions can be linear. This is pretty much what people expect, I believe. It's certainly what I expect.

I consider the aircraft following a vertical flight path I can't see on the screen during planning, nor can reasonably predict to be a serious limitation of the feature.

Thank you @Droning on and on... for your knowledgeable input on this issue. I’m surprised that more of us haven’t experienced this behaviour, which in my case nearly cost me a brand new Air 3. Hopefully DJI will provide a software update ASAP to rectify this before more of us lose their drones?

 

[DJ Wes]

That's the explanation, but it's not an excuse for this behavior.

Lazy programming. There's no reason the curve has to be fit in 3D. The curve can be computed in 2D, and altitude transitions can be linear. This is pretty much what people expect, I believe. It's certainly what I expect.

DJI uses a Centripetal Catmull-Rom spline to define the flight path. A Catmull-Rom spline has C1 continuity. If you are not familiar with parametric continuity you can read about it here:

Smoothness - Wikipedia

en.wikipedia.org

When compared to other types of splines, the Centripetal Catmull-Rom spline provides some features that are well-suited for drone flight paths. If a Catmull-Rom spline was implemented in 2D and altitude transitions were made linear, it would result in a path that has C0 continuity. This means that the 1st derivative at the waypoints would not be continuous and would require infinite acceleration at those points. This would be similar to a straight-line mission where the flight path abruptly changes at the waypoints. Litchi and DJI handle such cases by having the drone stop momentarily at each waypoint. The WPML language used by DJI calls this waypoint mode "toPointAndStopWithDiscontinuityCurvature".

Additionally, if a spline with C0 continuity was used to define a flight path in which video was captured, the resulting video would have abrupt changes at the waypoints rendering the video less than pleasing.

What DJI has implemented is not "lazy programming" with regard to the use of a spline. It is the correct implementation of a Centripetal Catmull-Rom spline applied to waypoints in 3D space. What DJI could do is to provide some stats such as the minimum (and perhaps maximum) heights of the resulting flight path. DJI's implementation of waypoints has always seemed like more of a proof-of-concept where only the most basic waypoint functions are provided. Applications such as DroneLink or Litchi provide more advanced waypoint design features making the creation of waypoint missions much more efficient.