Does QField know the CRS of the coordinates provided?

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1

Hi,
Something I never really thought about, but how does QField reproject data from the gps-device (internal or external) to the CRS of the layer where the coordinates are stored.

In QGIS, I have to manually reproject data if, for instance, I have a file with coordinates in 4326 and I want to store them in 8857.

Is QField doing the transformation automatically? A GPS device sends coordinates in a given CRS (and for my internal gps I actually don’t even know which one this is) and I create a layer to store my points in 8857. It works, but what actually happens?
This suggests that QField:

  1. knows the CRS of the received coordinates, but does it?
  2. does a transformation in the background and thus has access to relevant proj information?
  3. writes the coordinates using the CRS of the layer

See also this older topic: Add way to set CRS of data from GNSS receiver · Issue #2855 · opengisch/QField · GitHub

So I think my main question here is, how does QField know the CRS of the provided coordinates from the GPS used?

2

Hi @Jeroen-GroeneBij Literally 10 minutes ago, I spoke to @Mathieu_Pellerin about this. QField treats every external GNSS position signal as WGS84. When you then use a different projection / CRS in your project, this may lead to according shifts.

If you are using the internal GPS of your phone, the accuracy is appr. 5 m by default, hence you would not necessarily notice the offset.

Best

3

Aha, and by WGS84 you mean EPSG:4326?

And what does this mean when using an external GPS with RTK corrections? Some of those devices or RTK services have the ability to set an output CRS.
QField does not consider the output CRS?
So the output for these devices or services should be set to 4326 in order for transformation to the datalayer CRS to be correct?

Should this be mentioned in the docs?

4

You are absolutely right with your guesses.
Yes I mean 4326 and regardless of what CRS is put in the RTK device, QField will treat it as 4326

Yes - It is now on my list of things to put in the docs..