For some pictures, I got a message saying "Please specify at least 6 correspondences for further processing". I don't see that message for other pictures, why?
When the message is displayed the metrology engine has failed to infer the movement of the camera in between the two camera shots automatically. You can still process the pictures even if you see the warning message. However, you will have to specify at least 6 pairs of corresponding features (including the reference) to obtain measurements.
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