How to successfully align images from Pix4D Catch app project

[jkova96]

Hi dear Agisoft Metashape team,

I want to know what should I do to successfully align all images used in Pix4D Catch project, which is by the way aligned well.
So, to be honest with you don't know what should be the reason for that cause all photos submitted are same resolution as Pix4D Catch images are.

Image overlap is about 90% (see pictures within this link: https://drive.google.com/drive/folders/1V1RyRk-S-014fUtl7o1lQ7VzrIVDLX1L?usp=sharing )

I don't know what to say but difference between alignment results done in Pix4D cloud and Metashape are enormous.
See pictures below for differences.

Pictures - from Pix4D cloud: https://drive.google.com/drive/folders/1V1RyRk-S-014fUtl7o1lQ7VzrIVDLX1L?usp=sharing
Pictures - from Agisoft Metashape: https://drive.google.com/drive/folders/1A_lmgqdIlY3gphgnwzKeuoue8CfSBth9?usp=sharing

In fact best mesh what I got from Pix4D Catch images is generated with help of this script - https://github.com/agisoft-llc/metashape-scripts/blob/master/src/quick_layout.py
When I apply this script then I got, at least, complete model (I mean model with all images covered)

My settings are, source preselection - with  70 000 key points and 20 000 tie points. No masks used. (But take in consideration that no masks are used for processing in Pix4D cloud too)

Agisoft Report is available in file accessible here: https://drive.google.com/file/d/1Vmfa8rY0x_7ORxpk1hFcClaZUk_GuAWS/view?usp=sharing
Here's comparison, down below.

3D Model from Pix4D Catch: https://skfb.ly/pqRsw
3D Model from Agisft Metashape, quick layout script used: https://skfb.ly/pqRs6
Pictures showing difference between Agisoft Metashape quick layout (best look) VS Pix4D Catch/Cloud result: https://drive.google.com/drive/folders/1QM6wWAf8USRrMHS9l6n4F_9jZtEwXUYD?usp=sharing
Used photos submitted are available through this link: https://drive.google.com/file/d/1XlAqLBvu0LSfIZLf_CGdmuFn54foC3m7/view?usp=sharing
More informations, with included photos (I mean, informations about gps pose and etc) are available through this link: https://drive.google.com/file/d/1U2lQgqGr4pwyblrfchDAiOd2Eyy_2UCD/view?usp=sharing


I know that's too much informations for you, but MEAN QUESTION IS - WHY?! - I'm getting these results, wrong results...Please help. I just want to align these images perfectly without any help out of Agisoft Metashape (I mean without using script as quick layout script). Tips are also well included. Thank you. Hope you can get better results, cause in this case Pix4D wins...if someone (me or anyone) figure out how to align photos than Agisoft wins.

[James]

Hi jkova,

sorry i was in a bit of a hurry and didn't have time to read or look at everything you posted, but did manage to download and align all your images!

metashape really doesn't like image that are taken moving 'forwards', or images that are extremely similar to subsequent/previous images.

i added all images and checked the 'rotation/yaw' checkbox for all images though i don't think that had much effect in this case, but i did it so i mention it.

i aligned all images using generic and reference preselection, ignoring the warning that the capture distance wasn't specified.

all images aligned and it was garbage as expected.

i then reset alignment for all images. at this point the key points are still present and you can then re-use those to align selected images more deliberately.

i switched the photos pane to small icons and resized it so it was 7 columns wide. 8 or 10 or 5 would have probably also been fine. i then selected a single column of images by clicking and dragging over them, so i effectively select every 7th image.

then i right click and select align selected images. this way it is not trying to align images with virtually identical neighbouring images, and gives it a better chance to work out some proper geometry.

then i selected another column of images, and then repeated and so on, as shown in the attachments below and you can download the project here:

https://we.tl/t-gk5Zxf9oE7

You can align the remaining images if you like, but i suspect that 3 sevenths of all of those images is actually plenty!

[James]

last 2 attachments

[jkova96]

Hi dear James,
You maybe don't have idea, how grateful I am to you!!
This what you done is true kidness, because you take time to help me, and analyse all these things what I mentioned in post.
Definitely, If I was from Agisoft - I would you give you an reward, definitely deserved, cause you know this program so well.
BTW, I was unable to open your project since my Agisoft Metashape version is 1.8.5.
I would like to see exactly what you done in PSZ file which was sent to me.
But, no matter that, I did it how you describe it.
Every single step I followed, and I don't know why Agisoft "hates" so good overlaping images.
I think that overlap was, according to Pix4D Catch defaults,  90% (see picture below)
I choose first, fourth and last of 7 images in each column, like in picture (see that below)
...and I got best model from NO USING ANY SCRIPT!
I want to show you, if you interested, at least to see how all looks now, and this is link to my final result: https://skfb.ly/pqSOJ
OBJ Model for downloading is here: https://drive.google.com/file/d/1PjnXuoF-WbzRGfN947cFL-KSp9RTvuR-/view?usp=sharing
And got Processing report too: https://drive.google.com/file/d/18i-JazzeN3vCm7ax0ZSC7VOVXpY0nI9U/view?usp=sharing
And, yeah...I think you're best engineer in your field, whatever that field is. 

Thanks once again, and have a nice day!!

Bye

J.K.

[Alexey Pasumansky]

Hello Josip,

Due to the specifics of the shooting scenario in this project (very oblique angle for most of the cameras - 45-65 degrees for pitch) ​please consider using the following steps after adding the images to the project:

- uncheck all cameras in the Reference pane,

- then in Align Photos dialog disable Reference preselection option and use only Generic preselection.

After the initial alignment is finished, check that all the cameras are aligned correctly and there are no blocks of incorrectly aligned cameras. If there are any, reset alignment for them, then select them in the Workspace or Photos pane, right-click on selection and choose Align Selected Cameras option in order to re-align them - usually it helps to position the cameras to the right place.

After all the cameras (or almost all) are properly aligned, check on all the cameras in the Reference pane and press Update button on the pane's toolbar in order to apply georeferencing.


The project obtained following this approach can be downloaded by the link (saved in 1.8 compatibility mode):
https://www.dropbox.com/scl/fi/l149pr6t03gdcl863408w/josip_205004_model_1.8.psz?rlkey=ms933da9na3p0zbz7qbcojpqr&st=juddl3cp&dl=0


Actually, I would not call it "good overlap" when one part of the area is two meters apart from the camera and another - 10 meters away. For such project near nadir shooting scenario will be much better (for example, mount camera on a 1-2m pole and point camera almost vertically down, but so that it does not see the person carrying the pole and his shadow).

[jkova96]

Hi Alexey,Before starting my answer I can say that I'm grateful to you for analysing my dataset.
BTW...I'm always grateful when someone from tech support contacts me back, cause then I'm sure for getting the correct answer.

I can't imagine how great a result, I mean excellent result you've got!! You're definitely an expert! Of course I'm satisfied with your result.Hope what you described is now a workflow for highly oblique shoots, I wonder in which cases I should only use "Generic" preselection  Thank you so much for sharing your project with me. It's much better comparing what I got, also you can see what I got via this link, just reminding you: https://skfb.ly/pqSOJ
For someone who will, maybe later, face with this issue, or similar - I'll upload your project to this link: https://mega.nz/file/cSJmAQTJ#B6IYX-Q7gauCM1QcKQcrsRkHmwlUkbk5T4HCRorIiSE
You can (and everybody interested) download project whenever you want, better said whenever a link from Mega.nz survives.

Best regards and have a nice day!

J.K.

[Alexey Pasumansky]

Hello J.K.,

Reference preselection is mostly recommended for nadir aerial surveys. If there are oblique images, then Capture Distance should be properly defined before running matching with the reference preselection enabled.

[jkova96]

Hi Alexey,
Thanks for reply.
Can you tell me how accurate should be distance capture, and what exactly distance capture means - if images are oblique?

In my case, does it mean distance to ground - perpendicular from my position (vertical distance to ground)? I take photos in upright position, standing position, but camera was pointed downards and it was angled too.

Have a nice day!

J.K.