Multicamera alignment issues

[Echostorm]

Hi guys

We are having an issue aligning our three camera capture. We had a perfect capture, with 70% side lap of the three (incorporating the oblique angle) with 10% nadir (sidelap covered by the obliques looking over the Nadir). Really having trouble trying to get a solid align regardless of the settings I try. The runs seem to stick ok but do not align with the corresponding runs. In theory this should produce an excellent result. In practice, it doesnt.





I have attempted to run a camera calibration per camera separating the 3 cameras, however, it is still the same issue. Any ideas?

[Echostorm]

Here is a cleaner variation. Driving me insane!

[Alexey Pasumansky]

Hello Echostorm,

Were all three cameras taking images simultaneously? If so, are you using multi-camera system approach for processing.

[Echostorm]

Hi Alexey,

Cameras shot simultaneously (well within a few hundred milliseconds).


As far as multi camera setup, I have broken the cameras up in the camera calibration section. However still same issue as if they were all just merged in the one calibration group.

[Echostorm]

Note the 50mm lens is different on the Nadir camera, where the port starboard is a different 50mm lens. I have also tried 85mm lens port and starboard with the same bad results.

[Paulo]

Hi Echostorm,

if you are using a fixed rig with 3 cameras shooting simultaneously, then I would try using nadir as master in Calibration pane... for that you may have to import the photos as nadir, port, starboard stored in different sub folders of principal and use Import from folder option see

When you have separate synchronized sensors it is suggested to use Multi-camera system approach. In you case:
1. Create a new directory and then two subdirictories in it. Call them "1-RGB" and "2-IR", then put the images to each folder coming from the certain sensor - the order of the images in the folder should correspond to each other.
2. In Metashape interface use Workflow Menu -> Add Folder option and point to the "master" directory created in the beginning of the previous step. In the Add Photos dialog shown shortly after the folder contents are analyzed, select Multi-Camera System approach - > "Create sensor from each subfolder" option.
3. After loading images go to Tools Menu -> Camera Calibration dialog and, if necessary, enable "Reference" option for the slave sensor. In case the offset between the sensors cannot be neglected, then enable also "Adjust location" option. Additionally make sure that Layer Index in the Bands tab is different for Master and Slave sensor.
Approach would work if the sensors are synchronized and their relative exterior orientation doesn't change during the capturing process.

Also what is nadir overlap from one line to next? If it is 10% as I understand, it may not be enough....

[Echostorm]

I understand what you are saying about only 10% side lap for Nadir not being enough, however techinically it is 70% side lap, as the oblique cameras are still 50mm and they cover the Nadir area on either sides so plenty of side lap, one would assume that these would calculate as cameras at an angle. I do like how you have the sub menu style though. I will give that a go but I am not optimistic. It would be good to be able to allocate a single plane within agisoft for the scan type, i.e. height field vs arbitrary in the align process.

[Echostorm]

What is curious, is the actual oblique and nadir align, its the runs that dont despite the solid side lap.

[Paulo]

I think you should check matches between one nadir photo and other photos on another line.. with View matches context menu command of selected image...

It seems there is a lack of matches between lines...

[Echostorm]

No luck with the multicamera setting. The few microseconds between captures will likely not let this succeed.

I can't get tie points between Nadir runs when processing with multiple cameras so I cannot get these to display and send to you. 

It is something else and not an overlap issue as I can get it to stick by removing the nadir and only keeping oblique, likewise I can get it to stick (not very accurately) with Nadir only too although at 25% it isn't great). The forward lap is about 95%.

So that makes me think that the Nadir being a different lens type is causing issues. See photo of overlap with all three frames, with POI highlighted for overlap reference.

[Echostorm]

Won't let me post any more photos. See link https://ibb.co/mNbRzRq

It is exceptionally clean data, no pixel movement, no lens blur, optimum lighting conditions, minimal shade movement between runs.

[Matt]

Hi Echostorm and Alexey,

I have been having similar problems trying to align images from an A3 aerial surveying camera.
I found that using Photoscan 1.2 - 1.4.3 I was able to align the images with more success. If using the default settings High 40000/4000 doesnt work I found that aligning at low using 20000 key points and 4000 tie points or loosening the marker and tie point accuracy may also help with your alignment issues. 
If you still have issues i suggest using some tie points or control points.
Alexey can you please supply some feedback as to why the more recent versions of Metashape are not aligning complex camera scenarios.
I have been using Agisoft since beta and alignment while a lot faster now is not working reliably for my needs.

Many Thanks

[Echostorm]

Thanks Matt,

Yes I have definitely noticed this in the later version, also coming from the Beta days. 

Here is a visualisation of my swath https://imgur.com/eMJv34M

as well as result of my oblique only (Nadir disabled) align... https://imgur.com/a/jioLHsJ as you can see it works, ergo we should meet the side lap requirements, although in the ortho I am getting the odd double up.

[Alexey Pasumansky]

Hello Echostorm,

I could recommend to disable the pre-calibration parameters and allow Metashape to use autocalibration for all the sensors. If it doesn't help either, would it be possible to share the sample image set that can be used to reproduce the problem with support@agisoft.com?

[Echostorm]

Hi Alexey, I will send across the sample dataset.