In order to solve the problem of the three-dimensional deformation measurement in mechanics experiments
a new deformation measurement system based on stereo vision
photogrammetry and a digital image correlation method is proposed and implemented. The key technologies applied in the system are studied
including binocular camera calibration
image correlation algorithms
three-dimensional reconstruction and the calculations of three-dimensional displacement and strain. Firstly
a new camera calibration algorithm based on the photogrammetry is proposed
in which a 10 parameter lens distortion model is adopted to achive a reliable camera calibration result without any accurate calibration pattern. Then
the high precision image correlation is realized by using a least-square nonlinear optimization algorithm.To solve the problem in calculating initial values for the nonlinear optimization
a method based on seed points is proposed to provide a reliable initial value for the least-square nonlinear optimization. Finally
the approaches used for three-dimensional reconstruction and calculating three-dimensional displacement and strain are presented in detail. Experimental results show that the RMS error of the calibration result is 0.03 pixel
the accuracy of image correlation is about 0.02 pixel
and the measurement accuracies for the static profile
displacement and the strain are 0.05% and better than 0.5%
respectively. Compared with the traditional measurement method
the system can be more accurate
comprehensive and intuitive to achieve the measurement for displacement field and strain fields.
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references
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