Shift of ortho image upon exporting

[Rockflower]

I am having the same problem. Ortho images in Metashage have good alignments with GCPs, but once I exported to TIF, they shift randomly by half to a meter.
The coordinate system I am working on is NAD83 State Plane for Metashape file and GCPs. The location file of photos is in WGS83.
Export Orthomosaic function in WGS83 and NAD83 State Plane give different results.

[Alexey Pasumansky]

Hello Rockflower,

Can you please confirm that you are using only GCPs for the model referencing and the cameras are unchecked during the optimization procedure?

Do you have any check points for the project, which are not involved in georeferencing operation, but can be used for the accuracy validation.

NAD83 has different sets of ToWGS84 parameters, depending on which one you are using, the export result may be different.

[Rockflower]

Dear Alex,

Thank you for your reply!
I have checked the cameras upon optimization. This may have caused the shift upon the export?
I have more than ten GCPs and they can be used for the check, but I used them all for all procedures this time.

The same problem repeated when I set all the coordinate (project, camera, and GCP) as WGS84.
Exporting orthos in different projection gives different shifts even though they will be shown converted to the same projection of the map file in ArcGIS.

When I look the ortho in the Metashape Ortho tab, all the GCPs locate exactly on the GCPs, but they shift significantly upon export...

[Matt]

Try resetting the Z axis in the model. There is a python script I have used in the past attached.
This can sometimes shift out of alignment when dealing with old imagery.

[Rockflower]

Hi Matt,

Thank you for your comment! Let me have a look at the script and try.

[willcodeforfoo]

I've just started noticing the exact same issue with some historic aerials we are processing... GCPs are dead on in the ortho view but when exporting they shift. Our project is WGS 84, but exporting to MBTiles as EPSG:3857 and TIFFs as WGS84 and EPSG:3857 still have the same issue.

[Duncan Bourne]

Has there been a resolution of this issue? I'm having a similar problem: both markers and orthomosaic retain their alignment to each other but are misaligned with the basemap when exported.

[dsmapping]

Has anyone figured out how to fix this? Very frustrating

[Alexey Pasumansky]

Hello!

Do you use Check Points (markers that are not checked on in the Reference pane) for the accuracy validation in the project? Do the check points show low error in the Reference pane for the project?