Why? Total number of matchings between 2 images depends on other images.

[Ryuseiken]

Hello.
I'd like to ask why the number of matchings (valid + invalid) between a pair of images depends on the existences of other overlapping images.

Suppose I have 100 images taken from UAV, with the overlapping ratio of 80%.
The number of total matchings (valid + invalid) between the 50th and 51th images, obtained by "Align Photos" command, significantly decreases if I do not include any of other 98 images in the chunk.

The number of total matchings between any pair of images seems to be large when the chunk contains enough images in the surounding areas.

I am asking why this happens, because it is not likely to happen in principle.

In my Alignment, both of the keypoint and tie point limits are disabled. The result is the same if I use the default value of 50000 for the key point limit.

Thanks for your help.

[ManishSahu]

This because matches are also filtered based of spatial location and orientation (Look for fundamental matrix outlier detection). This will calculate relative location and orientation of multiple images  and if certain match pair don't satisfy this constraint then it will be rejected, hence they depend on surrounding images,

[Ryuseiken]

Thank you for your quick and informative response ManishSahu.

In my understanding, such matches (that do not have enough geometrical consistency with the estimated relative camera positions and orientations) are labeled as "Invalid" in PhotoScan.

The strange point is that, not only the numbers of "Valid" and "Invalid" matches between a pair of images, but also their sum, is affected by the existence of surrounding images.

In addition, even the total number of the key points (feature points) in each of the two images is affected by the existence of surrounding images. It seems to decrease when the surrounding images are not included in the Chunk.

I appreciate your further replies.

(PhotoScan 1.4.3 Professional)