Telecentric lens external parameter calibration method based on normal vector

Abstract

The invention provides a telecentric lens external parameter calibration method based on a normal vector, and relates to the technical field of machine vision application, and the method comprises thesteps: obtaining a first world position coordinate of a displacement platform; adjusting the displacement table to obtain a second world position coordinate and a third world position coordinate of the calibration point, and obtaining a direction vector according to the second world position coordinate and the first world position coordinate; obtaining pixel position coordinates of the calibration points; obtaining a homography matrix according to the pixel position coordinates and the third world position coordinates; decomposing the homography matrix to obtain a first part of elements and asecond part of elements; performing processing according to the first part of elements to obtain third-row first-column elements and third-row second-column elements; obtaining a normal vector of theplane calibration plate according to the rotation matrix; calculating an included angle between the direction vector and each normal vector, and taking a parameter corresponding to a minimum value inthe included angles as other elements of the rotation matrix; and performing processing according to the direction vector and the second part of elements to obtain other elements of the translation matrix. The calibration precision and stability are effectively improved.

Description

technical field [0001] The invention relates to the technical field of machine vision applications, in particular to a method for calibrating external parameters of a telecentric lens based on normal vectors. Background technique [0002] Telecentric lens (Telecentric) is mainly designed to correct the parallax of traditional industrial lenses. It can be within a certain range of object distance, so that the magnification of the obtained image will not change. is a very important application. Due to its unique parallel optical path design, telecentric lenses have always been favored by machine vision applications that require high lens distortion. In the image measurement process and machine vision applications, in order to determine the relationship between the three-dimensional geometric position of a point on the surface of a space object and its corresponding point in the image, it is necessary to establish a geometric model of telecentric lens imaging. These geometric ...

AI Technical Summary

Problems solved by technology

[0003] In the prior art, during the calibration process of the telecentric lens, since the telecentric lens is a parallel projection, the sign of the pitch angle and the roll angle in the external parameter Euler angle cannot be determined through the obtained two-dimensional image, so it is necessary to add an additional distance The positive and negative signs of pitch angle and roll angle are determined by surface points, which brings inconvenience to the calibration process; at the same time, in the process of telecentric lens calibration, it is generally considered that the movement direction of the translation stage is determined by the movement of the plane calibration plate placed on the translation stage. In the actual process, the movement direction of the translation stage is approximately parallel to the normal vector determined before and after the movement of the plane calibration plate, but there is a certain angle, which leads to errors in the calibration results

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