I am trying to plan a flight of a slope that is below me - is it possible to set the altitude to negative values?
To fly your drone over a slope below where you are standing, you could do a free flight mission as you cannot select a negative altitude in the app.
In the app, when you plan a drone mission, you have to set the flight height. It is relative to the altitude of where the drone was turned on and gets satellite signal (see article). It is not relative to the altitude of the homepoint (takeoff site), nor the starting point (drone position for the first picture).
For example, if you choose a flight height of 50 meters, the drone will fly 50 meters above the ground (i.e. the place it was first turned on) for the entire mission.
Side note: when dealing with slopes, it is best to keep approximately the same distance from the ground. You can consult the Image Acquisition Plan for Terrain with Height Variations article.
are you from the Pix4D support team? I have made different experiences with the flight height. Some weeks ago i made 5 flights for one project. Four with 40m and one with 90m height. I turned on the drone on a roof (about 20m high), a colleague took it, went downstairs and put it on the ground and then i started the Image aquisition from the roof. The (computed) camera position shows, that the flight height was about 40m (respectively 90m) from the ground. I don‘t know how Pix4D and DJI manage the height! The GPS coordinates in the EXIF data is useless in my opinion (look at my answer in the processing forum — coordinate system problem). The GPS height seems to be used (relative to take off position) but not saved correctly to the EXIF data. That is the only explanation i have got at the moment.
best regards Martin
Yes I am part of the support team and check out this post. We’ve known about the issue concerning elevation data saved in the EXIF file for images acquired with DJI drones.
Hope this helps!