Align drone photogrammetry with a terrestrial scanner point cloud

[Stef]

Hello, I've been widely searching for this subject but found not a proper solution, so I'm starting a new topic.

My purpose is to merge drone photogrammetry with terrestrial scanner point cloud, pretty much an actual theme. I'll list what I am trying to do:

• create 2 chunks, one for the photogrammetry data, and the other one for the scanner data
• in chunk #1 load all the drone photos and produce the dense cloud, referenced by GCPs in use
• in chunk #2 import the scanner point cloud, unreferenced (Local System), using a .E57 file published by Cyclone REGISTER 360
• align and merge chunks

I was expecting to simply pick common points and all come in place at once. Evidently I'm thinking wrong, because 'Align chunks' function is greyed and I can't execute it, probably because chunk #2 is not referenced.
The only thing about this argument I've found so far is this article from the helpdesk.

Isn't enough to have one chunk referenced for the alignment to happen?
I have a drone and a Leica RTC360, what is the procedure I should rely on, to merge everytime the work of both instruments in Metashape?

[Alexey Pasumansky]

Hello Stef,

If you can get structured scans from Leica RTC 360 in E57 format, then I'd recommend to follow the approach mentioned in the article that you are referring to. Following it you should be able to align the photos from your drone with the laser scans and reference the complete solution using the GCPs. Then generate the surface (mesh, DEM or dense cloud) using the depth maps source, that will use both depth data fro the laser scanner and from the photogrammetric reconstruction.

[Stef]

Thank you Alexey, I'm actually trying to follow the helpdesk article and I'll be back maybe tomorrow with the results.

I'm most doubtful about what will happen to the scanner registration. Because Cyclone REGISTER 360 already did the registration of the stations and it is very precise (globally ±3mm), so the thought of scanner spherical photo aligniment is scary, to say the least.

[Alexey Pasumansky]

Hello Stef,

I'm not sure, how you wish to keep the original registration of TLS data, but have it georeferenced in geographic coordinates?

If you mean keeping relative orientation of the TLS positions, then I could suggest the following workaround that, as I assume, should work for this task, although, I haven't yet tested it on real data:
- align TLS data with the drone imagery as described in the tutorial,
- set coordinate system for the chunk (including cameras and markers) to Local Coordinates in the Reference pane settings dialog,
- place marker projections for GCPs both on the drone photos and on the spherical panoramas,
- uncheck all drone cameras and markers in the Reference pane,
- check on TLS cameras (which have local coordinates) in the Reference pane,
- press Update button on the Reference pane toolbar
- reset alignment for TLS cameras,
- use quick_layout.py script (https://github.com/agisoft-llc/metashape-scripts/blob/master/src/quick_layout.py) to apply the source registration information to the TLS cameras,
- uncheck TLS cameras in the Reference pane,
- input markers' coordinates to the Reference pane in geographic/projected coordinate system,
- check on all markers in the Reference pane,
- in the Reference pane settings dialog switch the chunks' coordinate system to the geographic/projected system used for the GCPs measurement,
- press Update button on the Reference pane toolbar.

I think I haven't missed any important steps here, but as mentioned above, haven't yet tried it on real data myself. If you are going to try that on your project data, you may start with the sub-set to reduce the processing time.



Maybe you can falso ind some additional ideas in the following thread related to the TLS data processing:
https://www.agisoft.com/forum/index.php?topic=12997.0

[Stef]

Thanks a lot for what you're doing Alexey.

Basically, I need to complete the terrestrial scanner cloud with the data collected from air, for rooftop, balcony and such. Laser scanner point cloud is already produced and registered, I do not want Metashape to build it again from dome photos, it would not make sense. I just want Metashape to take the scanner cloud as it is and align it with photogrammetry cloud. Since a year I'm doing this align operation using CloudCompare, which is a powerful tool but not so stable and reliable, so I think it is time to learn how to do it in Metashape.

The process you listed seems like complicated, I'll read carefully every step and I'll try to apply it to my case. I'll be back with results as soon as possible.

EDIT: Thank you for pointing me to the linked thread 'Import Laserscan data -registration lost'. That is exactly my same situation, I'm going to read it all and see what the ending conclusions are, if any.
In my mind Metashape should not try to align or position anything when dealing with stations, it is counter-productive because the (relative) position in the 3D space is already given. Metashape should just take it and eventually transform coordinates to align and match it to its georeferenced photogrammetry cloud.