Import Laserscan data -registration lost

[Paulo]

Hello Bassistas,

running the quick layout scrit will assign Estimated EO from the source values but not generate tie points. So to generate the tie points you should use Tools > Tie Points > Build Poind Cloud command (assuring that you set Keep Key Points option in Preferences settings). Then you can import photos and do alignment in incremental fashion. However, if you wnt to keep the Laser scan registration, give them a very high accuracy in m and degrees....

The other alternative is to measure a few well identifiables features in the laser scans, and use these feature points as GCPs to align the images in separate chunk as specified by Dieter...then merge chunks...

Hope this helpful,

[bassistas]

Hello Bassistas,

running the quick layout scrit will assign Estimated EO from the source values but not generate tie points. So to generate the tie points you should use Tools > Tie Points > Build Poind Cloud command (assuring that you set Keep Key Points option in Preferences settings). Then you can import photos and do alignment in incremental fashion. However, if you wnt to keep the Laser scan registration, give them a very high accuracy in m and degrees....

The other alternative is to measure a few well identifiables features in the laser scans, and use these feature points as GCPs to align the images in separate chunk as specified by Dieter...then merge chunks...

Hope this helpful,

Thank you, I'll give it a try, but what do you mean by "give them a very high accuracy in m and degrees"? Is there any setting for that?
I also tried to follow this tutorial I found here https://agisoft.freshdesk.com/support/solutions/articles/31000159101-terrestrial-laser-scanning-data-processing which at the bottom it says:
"If the project contains also the common digital images to be aligned, it is recommended to align such image set first and then load the TLS data to the same chunk and run the mentioned script. Note that the digital images alignment should be referenced in the same coordinate space as laser scanning data in order to be properly processed together."
But how this can work if you try to import registered scans on top of already aligned photos that are probably out of scale already? In my case a drone like the standard phantom 4 pro without RTK

[Dieter]

Wait a minute, if I do set the laser scans as fixed points and then do the allignment via laser scans and photos, the tie points must be generated in the scans and in the photos, or am I completely wrong? The same function also works with photos if I have RTK coordinates, what's the difference?

As I have already noticed several times here, I find it totally unfortunate to do an essential function of the program (setting the laser scans as fixed points) with an external script. I never know exactly whether the script is up-to-date or whether it still fits the new version. This function must be integrated into the main Metashape program.

[Paulo]

Yes Dieter,

the quick layout will only set the aligned  TLSs position and orientation to values from source. To get tie Points you must run Tools > Tie Points > Build Point Coud... (having previuosly set Keep Key Points option). And then you can add orther images and do an incremental alignment.... However the matching between the intensity based TLSs and optical images may not generate many points ...

So other options would be used GCPs measured from the TLS chunk in the added optical image chunk to aligne and then merge with TLS..

Eventually, I guess we could add the matchPhotos() + triangulatePoints() prcess inside a quick layout script to generate the tie points ...

[Dieter]

@Paulo

I've tested that again now. For me, the tie points are also searched for in the laser scans and compared with those of the photos. Of course you have to select all elements (photos and scans) for allignment. To be honest, I haven't even known the menu item you mentioned until today.

Dieter

[Paulo]

Hi Dieter,

what exactly were u testing? The quick layout script or trying to align all scans with images? Because it it is just a common alignment then of course you can just do a normal alignment with both TLSs and images.To keep scans original  reference fixed, set a very high accuracy on scans position and orientation...

[Dieter]

My approach:

1) Import scans
2) Quick layout script
3) Import photos
4) mark only the scans as reference with an accuracy of 0.001 meters
5) allign scans and photos

Tie points are determined in the scans and the photos and compared with each other. The coordinates of the scans are held as a reference system.

Dieter

[Paulo]

OK, I see,

but IMHO if you use the scans with reference marked with high accuracy then I do not see the utility of quick layout script....

[James]

but IMHO if you use the scans with reference marked with high accuracy then I do not see the utility of quick layout script....

Some TLS scans may not get aligned at all if they do not get sufficient tie points to other scans and images.

I guess the script ensures that these 'orphan' scans still end up in the result and in the right place.

Unfortunately this is not often enough part of my workflow for me to know it inside out yet, but it does seem that given that the discussion is ongoing it would benefit from some clarity from above. Part of the reason I don't do it more often is that I'm not confident of what the outcome will be.

Making the selection of markers for manually tying the photos to the scans part of the official workflow with proper tools would be huge. I use Cyclone for TLS and take a lot of time looking at the data in 3D to choose my reference points as accurately as possible. I'm almost always working with buildings, so I'm looking at windows and cornices etc, to get my points correct to within a couple of mm, which is not possible currently in Metashape just by putting a marker on a depth map in '2D'.

[jedfrechette]

I use Cyclone for TLS and take a lot of time looking at the data in 3D to choose my reference points as accurately as possible. I'm almost always working with buildings, so I'm looking at windows and cornices etc, to get my points correct to within a couple of mm, which is not possible currently in Metashape just by putting a marker on a depth map in '2D'.

I think this is the key observation that the Agisoft developers need to make if they want to make laser scan support actually useful in their product. Those of us coming from the TLS world have very good tools to make sure that our laser scans are very well aligned relative to each other as well as independent reference points.  In most cases those registrations are also much better constrained, and therefore more reliable, than pure photogrammetry solutions. As a result, just treating laser scans as low resolution panoramas and throwing them in to your bundle adjustment largely ignores their benefits and is never going to be a satisfactory solution.

Currently, the only practical method I've found for combining laser scans and photogrammetry with Metashape is the traditional approach of manually picking ground control points. However, that method is also time consuming, error prone, and requires jumping back and forth between multiple pieces of software. We've worked on a few Python tools to make it slightly less painful but the process is by no means as efficient as it should be.

[Dieter]

but IMHO if you use the scans with reference marked with high accuracy then I do not see the utility of quick layout script....

Some TLS scans may not get aligned at all if they do not get sufficient tie points to other scans and images.

That is exact the point!

I use Cyclone for TLS and take a lot of time looking at the data in 3D to choose my reference points as accurately as possible. I'm almost always working with buildings, so I'm looking at windows and cornices etc, to get my points correct to within a couple of mm, which is not possible currently in Metashape just by putting a marker on a depth map in '2D'.

Currently, the only practical method I've found for combining laser scans and photogrammetry with Metashape is the traditional approach of manually picking ground control points. However, that method is also time consuming, error prone, and requires jumping back and forth between multiple pieces of software. We've worked on a few Python tools to make it slightly less painful but the process is by no means as efficient as it should be.

If you take the scans and photos of the same objects (e.g. walls) and do the scan in color and choose the right exposure for the color scans, and also about the same resolution between photos and color scans, the photos are linked to the scans. It takes some practice and experience, but it works.

We often work like this, the base point cloud comes from the scans and inaccessible areas are condensed by photos.

[bassistas]

My approach:

1) Import scans
2) Quick layout script
3) Import photos
4) mark only the scans as reference with an accuracy of 0.001 meters
5) allign scans and photos

Tie points are determined in the scans and the photos and compared with each other. The coordinates of the scans are held as a reference system.

Dieter

I had some success with this workflow but in the case I already have a project with imported laser scans and photos with markers attached, if I disable all the photos and leave just the laser scans enabled after the execution of the quick layout script , I go to Tools-> Tie points -> build point cloud and it messes up the position of the scans for some reason. It brings all the scans to the same center like a ball.
If I create a new project and add just the scans first then this is working as it should but how can I make it work on an existing project in which I have more than 150 markers already placed on photos and laser scans and is a pain to place all of them from the begining?