Get mobile device orientation with respect to North

[ranleu]

I use QField to document landscape features. In many cases the azimuthal angle (alternatively the bearing) is of relevance.
Also when taking a picture it is usually relevant to know in which direction the picture was taken. I am a user and not a developer, so I ask a bit of patience. In any case I have tried to do my homework.

I will use the term DIRECTION in my question to refer to the angle with respect to the north (From 0 to 359). The term ORIENTATION is most commonly used for Vertical vs. Horizontal image "format".

I have been searching a lot and reading whatever I could find on this, but I am unable to find a concrete answer to the issue (at least at my knowledge level). Among the things that I have read are:

1. https://gis.stackexchange.com/questions/376773/direction-of-taken-photo-qfield
   --This one covers extraction of the ORIENTATION from the EXIF data from the picture. However, it should be noted that:
   a. Not all devices/apss store neither the orientation nor the direction in the EXIF data.
   b. If at all, then it is usually the ORIENTATION (Vertical vs. Horizontal) information that is stored.
   c. The discussion focuses on post-processing extraction.

2. https://gis.stackexchange.com/questions/388378/store-and-use-compass-and-dip-with-qfield
   -- This question is much closer related to my question, however the final answer is that is a feature request and there is a link to the request (see Nr. 3 below)

3. Feature request: geologic compass #1882
   -- There is an interesting discussion on the request, but no definite answer. However, from the last entry, I understand that information from a third party app (like Rockd) may be streamed through TCP or UDP sockets and captured by QField. This sounds promissing, but my development/hardware knowledge are not that far reaching, that I could setup something like this.

4. Enhancement - add expression variable to record Orientation #3072
   -- This one also seems to deal with my issue. It appears closed after pointing to https://github.com/opengisch/QField/blob/master/src/core/utils/fileutils.cpp#L209-L213
   Yet another discussion points to (which is similar to the previous one).
   https://github.com/opengisch/QField/blob/master/src/core/utils/expressioncontextutils.cpp#L64

However, I am uncertain if the GPS Orientation (whatever that means) will return the DIRECTION of say the picture/camera is pointo towards. Also, I can make little out of this code. I need to know how I would call this into an attribute on a layer.
Could it be as simple as using the variable @position_orientation or simply @orientation in an expression while setting up the QField project?

5. No more use of the Open Camera app and therefore less image metadata since Android 11 update #2042
   Finally, from the closing comments in this discussion, is this information stored per-default when using the BuiltIn camera? Which would again close the loop to the discussion presented in Nr. 1 above....pffffff

If it turns out that the solution is already there and it is just my lack of knowledge what is preventing me from solving this, I have the feeling that this is a quite common "nice to have" and would be much welcomed to have it clearly treated in the QFIELD Documentation.

[nirvn]

@ranleu , you came pretty close to the answer by yourself :)

you can use the @position_orientation (or @gnss_orientation when not locked into the gnss device's position during ditiziting) in a default value expression to retrieve that value while digitizing.

It should be added to the documentation here (https://docs.qfield.org/how-to/gnss/#positioning-variables).

[ranleu]

Thank you for the quick reply. Just for my understanding, is mobile devices magnetometer the source of the orientation for the @position_orientation variable?

[nirvn]

@ranleu , correct.