Study On The Measurement System Of The Windshield Of The Automobile Base On The Machine Vision

In order to solve the problem of the field measurement of large-size automotive windshields,a kind of system which is based on the marked point to measure the 3D shape of the car windshield is designed based on the theory of machine vision in this paper.The system mainly includes a binocular stereo vision measuring module and a projection module.After the measurement system is calibrated,the coordinates of the marked points in the camera coordinate system at the initial position are used to establish the specific glass coordinate system.The glass surface in the field of view is measured by projecting white cubes arranged in black background and coordinate-transformation is completed.After the measurement system is moved,the conversion relationship between the camera coordinate system and the specific glass coordinate system is obtained according to the coordinates of the marked points before and after the matching movement,and the projection and measurement is performed again.Multiple measurements of the windshield surface are achieved by moving the measurement system several times.The experiment results show that the projection and measurement method is feasible and economical.The main contents of this paper include:(1)The extraction and matching of marker points.The precision of the center extraction of the markers and the precision of the matching will directly affect the measurement accuracy of the whole measurement system.The center coordinates of the marked points of the imaging plane are obtained by using the center extraction algorithm of the sub-pixel,and the center coordinates of the marked points of the left and right imaging plane are matched at a high accuracy rate.(2)The establishment of the glass coordinate system and coordinate transformation.Firstly,the glass coordinate system is established according to the coordinates of the marked points in the initial position and the conversion between the two coordinate systems are obtained.After moving the camera,the conversion relationship between the camera coordinate system and the glass coordinate system is obtained according to the coordinates of the same marked points extracted from the glass coordinate system and the camera coordinate system before and after moving.(3)The projection measurement of the glass surface in the common field of view.After the binocular system is calibrated and the transformation relationship between the coordinate systems are obtained,the white squares on the black background are arranged with the projector,and the coordinates of the center point of the block of the image plane are extracted by using the dot extraction algorithm.After sorting and matching,three-dimensional coordinates in the camera coordinate system are got and the accurate measurement are completed.The innovation of this paper is to reduce the complexity and workload of matching through projecting ordered white squares and designing a method of establishing glass coordinate system according to the direction of the 3D vector in the camera coordinate system.This method is economical and practical simple,straightforward,and accurate.The only factor that affects the accuracy is the extraction accuracy of the marked points.The measurement of the entire glass can be done by moving the measurement system several times and completing the measurement and coordinate transformation in the common field of view.