I have detected a discrepancy between the mission information and the drone’s behavior
In RELATIVE frame, when defining a waypoint at altitude 0, the drone neither ascends nor descends from the previous point but instead flies along the established route without changing the flight altitude.
However, in the mission profile, the altitude graph appears correct.
The error occurs both in real flight and in the simulator. I have tried various combinations, and it always happens.
Very interesting. I just tried it in SITL and you’re right. I set a waypoint command with an altitude of 0 and the drone remained at it’s flight height. I tried with both relative and terrain frames. Same result.
The elevation graph did show a planned descent, but the drone didn’t do it.
That said, is this a bug or a feature? If you create a waypoint with a location manually the alt will default to 0, so this might save you from an unexpected dirt nap.
Edit: I just tried with -1m and the drone acted as planned. It descended to -1m. Obviously in the sim. 
Hi @Robotic,
Thanks for the report. This is the intended behaviour actually. zero altitude and/or 0,0 lat,lon will result in the vehicle using its current target (alt or lat,lon) for the waypoint.
We have discussed whether we should change this but this is how it’s always been.
Hello, thanks for the responses and try it !
I humbly believe it’s important that the behavior is modified
I’ve been flying missions for years, and this is the first time I’ve detected this behavior, and the first time it has occurred. I’m almost 100% sure that it didn’t happen with previous firmware versions (but its imposible argue to rmackay =)
Additionally, it’s very important to note that the mission profile graph (map tools - elevation graph) does generate the desired flight path exactly as we’ve programmed it. At no point does it show that the drone will maintain a straight line; instead, it graphs that the drone will ascend or descend depending on the situation as usual.
This discrepancy between the route graph shown by Mission Planner that the drone is supposed to follow and the actual behavior, which is different from what was programmed and graphed, means it definitely needs to be reviewed. Either to ensure that the current behavior is maintained and properly graphed, or to make sure the drone’s behavior matches the projected flight graph
By the way… unfortunately, I discovered this the hard way.
Ardupilot worked as documented here
Supported by: All vehicles.
Navigate to the specified position.
The Copter will fly a straight line to the specified latitude, longitude , and altitude. It will then wait at the point for a specified delay time and then proceed to the next waypoint.
Command parameters
| Command Field | Mission Planner Field | Description |
|---|---|---|
| param1 | Delay | Hold time at mission waypoint in integer seconds - MAX 65535 seconds. |
| param2 | ||
| param3 | ||
| param4 | ||
| param5 | Lat | Target latitude. If zero, the Copter will hold at the current latitude. |
| param6 | Lon | Target longitude. If zero, the Copter will hold at the current longitude. |
| param7 | Alt | Target altitude. If zero, the Copter will hold at the current altitude. |
Therefore, the bug is within the tool not ArduCopter itself.
Renamed the topic, as it is neither a bug nor worthy of an alarming caution. I understand your argument and will leave it to the team to review as needed.
