Best practice for dealing with inconsistent GPS datums?

[william]

In our UAV dataset, we have images with GPS tags using the WGS84 datum. Agisoft markers were used on the ground, and their locations were recorded in the NAD83 datum. We can expect that the GPS tags will therefore be shifted by up to 1m between the images and the markers. What is the best practice for the most accurate photogrammetry in Metashape?

1. Pretend all GPS tags are in NAD83, and set measurement precision of the camera reference entries to be lower (1m - 10m, compared with 0.02m for markers).

2. Remove the camera reference entries altogether, and generate the georeference only based on the markers in NAD83.

I would appreciate any input. Thanks!

[Paulo]

Hello,

if your drone has a normal GPS (not survey grade or PPK) then the camera centers will have an assumed accuracy of about 10 meters, so shift between NAD83 and WGS84 will be totally whithin GPS error budget.

And if you have cm level GCPs, I would just uncheck all cameras before your final optimization so only GCP markers will affect final adjustment...

Now in case you have a GPS RTK drone giving you cm level coordinates for your camera centers, then to correctly model discrepancy between NAD83 and WGS84, you would need precise toWGS84 datum 7 parameter transformation definition a liitle like following for NAD83 CSRS...(here ITRF14 is basically equal to WGS84):

*  ITRF14 -> NAD83(CSRS)
*  Reference ellipsoid: GRS80=WGS84
*  ITRF Epoch: 2010.000 (y)
*  Transformation Parameters:
*  [Rotations positive clockwise]
*  TX  =  1.00530 (m)        dTX =  0.00079 (m/y)
*  TY  = -1.90921 (m)        dTY = -0.00060 (m/y)
*  TZ  = -0.54157 (m)        dTZ = -0.00144 (m/y)
*  RX  = -26.78138 (mas)     dRX =  -0.06667 (mas/y)
*  RY  =   0.42027 (mas)     dRY =   0.75744 (mas/y)
*  RZ  = -10.93206 (mas)     dRZ =   0.05133 (mas/y)
*  DS  =   0.36891 (ppb)     dDS =  -0.07201 (ppb/y)

[william]

Thanks Paulo, very helpful.