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Author Topic: Georeferencing 3D scan with known position points  (Read 1327 times)

tinybear

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Georeferencing 3D scan with known position points
« on: April 08, 2022, 06:51:01 PM »
Hi everyone!

I'm back again with my faro cloud.

It is non-georeferenced, in Local coordinate system (m).

I have some reference points of known position in a projected CS LV1903+ (meters too).

I created markers on my point cloud; they of course display unrealistic Local XYZ values. Both markers and reference points represent the same points on the cloud.

I tried to manually change the XYZ markers + update.

How could I "force" Metashape to "move" my Local point cloud to a georeferenced one using GCP-like points?

Paulo

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Re: Georeferencing 3D scan with known position points
« Reply #1 on: April 09, 2022, 04:59:20 AM »
Hi tinybear,

i think you could probably do this with Cloud Compare and Align... look it uo and you will find many tutorials on the subject...

Best Regards,
Paul Pelletier,
Surveyor

tinybear

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Re: Georeferencing 3D scan with known position points
« Reply #2 on: April 09, 2022, 10:40:47 AM »
Hi Paulo!

I finally found the workaround:

Re-importing the 3D scan point cloud  and shifting the XYZ coordinates in "Import cloud" form with XYZ values of one of the known points. Thus, both clouds are "almost aligned" +/-10 meters and above all georeferenced in the same coordinates reference system.

The following workflow makes the final alignment very well:

1. Create Markers on the 3D scan (corners etc...)
2. Export Markers in txt
3. Transform WGS84 cameras geotags CRS into projected one (metric) : UTM, RGF93 etc. )in photogrammetric chunk
4. Align cameras
3. Import Markers  (tie points)
4. Align Markers with cameras (same corners etc. ) as with GCPs
5. Optimize
5. Generate Dense Cloud
6. "Align chunks" and "Merge chunks"

Done.  :)