How to align orthomosaics using external point cloud?

[ianMc]

Hi,

I am struggling with aligning orthomosaics using an external point cloud.

This is my initial workflow:
- upload georeferenced photos to Metashape
- align photos and create point cloud
- export point cloud

I then align the photogrammetry-derived point cloud to a LiDAR-derived point cloud using CloudCompare. This involves first retiling the photo-point cloud to a standard grid of 844 tiles.

What I want to do is then use this (now-external) aligned point cloud to create an aligned orthomosaic. However, this is not working. I've tried the following attempts:

Attempt #1
- upload aligned point cloud (844 tiles) and merge into single cloud
- create DEM, then orthomosaic
- Result = not aligned

Attempt #2
- upload aligned point cloud as laser scans
- create orthomosaic directly from the scans
- Result = exactly aligned, but the resolution is coarse and there are multiple blurry spots (still apparent even when using a higher-resolution point cloud)

Attempt #3
- (following this tutorial: https://agisoft.freshdesk.com/support/solutions/articles/31000168474)
- create new chunk
- upload aligned point cloud as laser scans, group them, change to Fixed, disable lock transform
- re-upload photos
- align the photos (now Metashape uses the laser scan info)
- build a new point cloud, then DEM, then orthomosaic
- Result = not aligned, but slightly better than Attempt #1


What I want is to get the output of Attempt #2 but with the orthomosaic using the photos. It seems to do that I would need to directly transform each individual photo but I have 844 transformation matrices and >1000 photos.

Is there another way I can get a fully aligned orthomosaic? I know the new point cloud is fully aligned but I can't figure out how to do this.