Why the key points change every time I run Align Photos?

[Ryuseiken]

Hello.

I have been wondering why the result of “Align Photos” command (e.g., the number and positions of points in the sparse point cloud) is different every time I run the command, even if I restart PhotoScan each time and use exactly the same setting.

Then, I have noticed that the number of the key points (feature points) detected in each image changes every time I run the “Align Photos” command. It means that the process is stochastic in its first stage: feature detection.

I understand if the optimization (e.g., bundle adjustment) process is stochastic, because stochastic strategy is sometimes useful to avoid local minima in optimization. However, I have no idea why the feature detection process should be stochastic, not deterministic.

Of course the detailed algorithm must be secret, but I would be happy if I can understand why it should be stochastic.