Hello Ben,

First I would be very suspicious if your camera coordinates from VRSNow RTK have a shift of some 1 to 2 m in E,N compared to your GCP RTK surveyed points. Are you sure they are in same datum? I think maybe your GCP reference Survey Mark coordinates were in GDA94 datum....see https://www.agisoft.com/forum/index.php?topic=12063.msg54003#msg54003 for difference between GDA94 and GDA2020...

Anyhow the X, Y, Z datum shift parameters that you are specifying are related to the geocentric CS (red axii in attachment) and not projected compound CS (E, N, H green axii). See folowing screen copy for representation of the different CSs. So you would need to do following:

1. find E, N coordinate values of some point in center of project P1 (Eavg, Navg, Havg)

2. transform to geocentric P1gc = chunk.crs.unproject(Metashape.Vector((Eavg, Navg, Havg)))

3. define second point geocentric coordinates from first point with offset applied P2gc = chunk.crs.unproject(Metashape.Vector((Eavg + 0.547, Navg + 1.545, Havg + 0.023)))

4. P2gc - P1gc should represent the off set in X, Y, Z for datum transformation (check sign for correct TOWGS84 transformation).

But again this is really not a rigorous procedure as it only takes into account 3 parameters instead of 7. And then you would need to define 2 datums: one for for markers (GDA94 ?) with these 3 calculated parameters and one for cameras with all 0 towgs84 parameters. Best would be to use the complete 7 parameters of GDA94 to GDA2020 or WGS94 transformation defined in above link...supposing that your GCPs are actually referenced in GDA94.

Hope this can help,

Hi Paulo (and everyone else),

Thanks for your great response, and you are correct, there are two different datums. The GCP's are on GDA 2020 Zone 56 but after reading your post, I did some digging, and it looks like the drone's VRSnow mount point (TVN_Nearest_RTCM_32) was transmitting on GDA94 Zone 56 datum.

I need all my data on GDA2020 + AusGeiod2020

One of the problems I’m having now is converting the image exif data (lat and longs) to GDA94.

I ran the "Convert Reference" from the Reference Pane - converting images from their exif WGS84 data to a compound co-ordinate system - that being GDA 94 / MGA zone56 + Aus Geoid 09, but the reference co-ordinates don’t change to Easting Northing. They stay at Lat Long? Has anyone been able to convert WGS 84 to GDA94 using the CS supplied with Metashape?

Previously when I ran convert using (the incorrect) WGS84 to GDA2020 it converted all image data to Easting Northing coords.

Am I correct in saying that if I could get the converter to work for MGA 94 then I could run “convert reference” again to convert from GDA94 to GDA2020? Then my images and GPS would be on the same datum.

Paulo did a great job of explaining my XYZ datum transformation parameters didn’t work (geocentric CS vs compound CS) but am I very new to this (this is the first P4 RTK using VRSNOW I have reduced) so could someone explain if Metashape has the functionality to do small Compound CS shifts by directly entering the shift needed? If the E, N, distance needed to shift the data is small (say under 10metres) shouldn’t that be doable with a command within Metashape? In my case it is E 0.547 N 1.545 H 0.023. Or is my only option to calculate the geocentric offset as Paulo detailed and enter it into the “datum transformation parameters” XYZ (m) shift?

Would it be a lot easier if in “datum transformation Parameter” there was the option to select either XYZ shift in Geocentric CS or XYZ shift E N RL shift in Compound CS?

Any help very much appreciated