Valid matches marked as invalid

[groob]

Hi Alexey,
For one of my sites, Metashape in unable to align almost half of the photos (437/721 aligned). The images are of good quality and resolution, and the software is finding many CORRECT matches between them, but marking them as invalid anyway! This happens at high and low accuracy settings...

Several other people have asked how the program decides whether a match is valid and I have not seen an answer yet. What is going on?

Thanks,
Sam

[Felix_]

This still remains a recurring issue for me. Could anybody help us out with this, please?

[James]

This is my theory:

I think the terms 'valid' and 'invalid' might be misleading. I think they more likely should be named 'used' and 'unused'.

A set of key points can only be 'used' to align an image if they are matched in two other aligned images.

See here for the full thread which will make it make more sense.

[Felix_]

Hey James thank you for your reply.
The need for a keypoint to be found in at least two other aligned images is a very helpful information. Somehow I missed that before. Thanks!

[Paulo]

Hi James,

I think your idea is not correct  Actually invalid points are points matched in 2 photos or more but not accepted during aligning process for not satisfying certain threshold (far,inaccurate,invisible,weak,,..).

So if you look at an image the grey points are matched points that were rejected during alignment or optimize process. Blue points are points that were accepted and valid... see attachment, where you can see grey points (invalid)  are present in at least 2 images...

[James]

I think your idea is not correct  Actually invalid points are points matched in 2 photos or more but not accepted during aligning process for not satisfying certain threshold (far,inaccurate,invisible,weak,,..)

I'm not sure that what you're saying and what I'm saying are mutually exclusive.

I agree that points that 'make it' to the invalid matches list will necessarily exist in at least two photos. If they didn't, they wouldn't be considered for alignment at all and therefore not be considered to be valid or invalid, just ignored completely (except for where you choose to retain key points, in which case they live to fight another day).

I'm not sure that I previously said anything to contradict that. If I did, then I admit that it was not correct!

[James]

Ah I guess it was this bit:

A set of key points can only be 'used' to align an image if they are matched in two other aligned images.

but 'can' only be used, and 'will' only be used are not the same. So I will admit my explanation was incomplete