Point Layer ITRF2020(PointPerfect) Transformation to Nad83(CSRS)V7(Project)

[DrawQuick]

I have a Qfield Cloud Project with the Project CRS set to EPSG(22717). I am connecting my gps receiver(U-Blox C099-F9P) to PointPerfect which transmits ITRF2020(quarterly Epoch EPSG:9989) correction data. I have set Transformations in the project settings 9989 to 22717, 22717 to 9989, 4326 to 22717 and 22717 to 4326. When I record a point with the Point Layer set to ITRF2020 the resulting project coordinate does not match NR Canada conversion.
Point Data Copied from QGIS
Lat: 43.91879931791666
Long:-80.09282190216666
h:387.6080522460936
x:572831.4388
y:4863254.0782
z:385.3951217

NRCan Transformation
Lat: 43.91879931791666
Long:-80.09282190216666
h:387.6080522460936
x:572832.234
y:4863253.035
h:388.704
Can someone tell me what transformation Qfield is using?
Should the point layer be set to WGS84(EPSG:4326)?

[nirvn]

@DrawQuick , can you share a sample project?

[DrawQuick]

Hi nirvn,
Attached is my project.
The points coloured Blue(Layer TestIRTF2020) are the ones I recorded at various times using the PointPerfect subscription service.
The points coloured Orange(Layer PointsN83V7) were recorded using my base station(RTK2GO - OvilleOne Base coordinates established using NRCan PPP).
Both sets of points were observed on the same point.
Project5540.zip

[nirvn]

@DrawQuick , OK, here's what is happening. While you GPS transmits coordinates in EPGS:9989, QField doesn't yet support custom CRSes from GPS devices. At the moment, QField hardcodes all coordinates coming from GPS devices as being EPGS:4326.

In your case, what it means is that the dynamic epoch of the 9989 CRS is not considered, and the coordinates are transformed using the fixed WGS84 EPSG:4326.

You can confirm this using the python console in QGIS. When handling your lat lon height point projected in EPSG:4326 using the simple script below, we end up with the "wrong" result when transforming to EPSG:22717:

point = QgsPoint(
    -80.09282190216666,
    43.91879931791666,
    387.6080522460936
)

crsFrom = QgsCoordinateReferenceSystem('EPSG:4326')
crsTo = QgsCoordinateReferenceSystem('EPSG:22717')
transform = QgsCoordinateTransform(
    crsFrom,
    crsTo,
    QgsProject.instance().transformContext()
)

point.transform(transform, transformZ=True)
print(point.asWkt()) 

>> PointZ (572831.4387031098594889 4863254.07845740206539631 387.60805224609362085)

However, if we project your point using the EPGS:9989 CRS and set the proper epoch (say June 2024, i.e. 2024.6), we get results that essentially agree with NRCan:

point = QgsPoint(
    -80.09282190216666,
    43.91879931791666,
    387.6080522460936
)

crsFrom = QgsCoordinateReferenceSystem('EPSG:9989')
crsFrom.setCoordinateEpoch(2024.6)
crsTo = QgsCoordinateReferenceSystem('EPSG:22717')
transform = QgsCoordinateTransform(
    crsFrom,
    crsTo,
    QgsProject.instance().transformContext()
)

point.transform(transform, transformZ=True)
print(point.asWkt())

>> PointZ (572832.23591925122309476 4863253.03488864377140999 388.70384873077273369)

The solution here is for QField to gain support for customizing the CRS for external GPS devices. See this enhancement request by fellow QField users (#2855).

This is a functionality I'm really hoping to implement on day. The wait period can be greatly shorten if this gets sponsored of course. If you are interested, let us know.