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Author Topic: Align photos - Tie points ghosting  (Read 3080 times)

frmgsft

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Align photos - Tie points ghosting
« on: February 11, 2021, 11:20:48 PM »
Hello Dears,
I meet this type of issue from time to time, please advise how to deal with it.
I got all cameras aligned, however tie points are split into a few groups of partial reconstruction. I hope the screenshot will explain everything.
What would be the best approach to workaround this? What settings should I tweak to get correct alignment? I use standard version of Metashape 1.7.1 if that matters.
I would greatly appreciate any hints.

Alexey Pasumansky

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Re: Align photos - Tie points ghosting
« Reply #1 on: February 11, 2021, 11:36:31 PM »
Hello frmgsft,

Please try the following settings:

High accuracy, Generic preselection - enabled, Reference preselection - disabled, Reset current alignment - enabled,
Key point limit - 40 000, tie point limit - 10 000,
Adaptive fitting - disabled, Guided matching - disabled, Exclude stationary points - disabled.
Best regards,
Alexey Pasumansky,
Agisoft LLC

frmgsft

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Re: Align photos - Tie points ghosting
« Reply #2 on: February 11, 2021, 11:55:32 PM »
Wow, that was quick. Thanks Alexey!
It looks better now - see screenshots.

frmgsft

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Re: Align photos - Tie points ghosting
« Reply #3 on: March 02, 2021, 04:35:33 PM »
What could I do if some ghosting occurs no matter what settings I use?
So far I used to filter photos by points/cameras/tie points, then remove or disable cameras and repeat alignment. That's quite tedious workflow. Are there any smarter alternatives?

Alexey Pasumansky

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Re: Align photos - Tie points ghosting
« Reply #4 on: March 03, 2021, 07:10:20 PM »
Hello frmgsft,

I would say that with the settings that you have mentioned before the alignment should be correct, providing that there is sufficient overlap between all the images.

If you are working with the Professional edition of Metashape try to uncheck all cameras in the Reference pane and repeat the Align Photos operation with the same parameters. If the problem persists, please save the project in PSZ format via File Menu -> Save As command with the latest results and send it to support@agisoft.com.
Best regards,
Alexey Pasumansky,
Agisoft LLC

frmgsft

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Re: Align photos - Tie points ghosting
« Reply #5 on: March 03, 2021, 09:01:50 PM »
Hey Alexey, I only have Standard edition. Do you need the psz file only or complete set photo captures as well?

Alexey Pasumansky

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Re: Align photos - Tie points ghosting
« Reply #6 on: March 03, 2021, 09:34:04 PM »
Hello frmgsft,

Just PSZ file (with the alignment results) without the complete image set would be sufficient at this point.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Alexey Pasumansky

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Re: Align photos - Tie points ghosting
« Reply #7 on: March 03, 2021, 09:57:19 PM »
Hello frmgsft,

Thank you for sharing the project file.

I have reset camera alignment for all the cameras in the project, then switched the camera type to Fisheye in the Tools Menu -> Camera Calibration dialog and then run Align Selected operation for all the cameras in the project. Visually, the result seems to be correct. So I can suggest to try the same procedure and see, if it helps.

‚ÄčIf the alignment results meet your expectations, shrink the bounding box to the area of interest and run depth maps based mesh generation procedure.
Best regards,
Alexey Pasumansky,
Agisoft LLC

cbnewham

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Re: Align photos - Tie points ghosting
« Reply #8 on: March 04, 2021, 02:50:51 PM »
I sometimes get this.

I found that the best way is to select the points of the "ghost" (or secondary object) and reset the cameras for it. Then align just those cameras in small batches. It usually works in aligning the errant pictures with the correct ones.

If you select "details" for your images after selecting and resetting the images from the "ghost" (and then removing the filter, to see all of the images again), you can then order the results by "aligned" and realign just those images. I suggest doing it in small batches, otherwise you can sometimes end up with the "ghost" again. It appears to sometimes depend on the order in which the alignment is done. Sometimes you just can't get all to align correctly, in which case just discard those images causing the problem.

There have been rare occasions where I have had several "ghosts" and a really messed up sparse cloud, but with some careful use of the above technique, managed to correct all of the problems by doing multiple manual passes of aligning sets of cameras.

I hope this helps.

Alexey Pasumansky

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Re: Align photos - Tie points ghosting
« Reply #9 on: March 04, 2021, 06:01:43 PM »
The new concept of "components" displayed in the Workspace pane that was introduced in the version 1.7 should help to see the major blocks of aligned sub-sets. However, in this particular project the problem was caused by incorrect camera type (Frame instead of Fisheye).
Best regards,
Alexey Pasumansky,
Agisoft LLC