Since the gear engagement is a common coupling form between rotors, the transfer matrix of skew gear engagement in global coordinate system is deduced based on the concept of coupling element.

Error locating for form data field because of form image deforming, skew, noise and shift when printing and so on will lead to data extract failure.

We use a vectorization algorithm to extract form lines from run length connect graph which is calculated first, and in the same time the skew Angle is detected.