Stereovision 3D Displacement Measurement Method Based On Two Coordinate Systems

To meet the requirement of non-contact measurement of 3D deformation of structure in Civil Engineering,this paper proposed two stereovision 3D displacement measurement methods based on two coordinate systems and two free laid cameras,respectively.The synchronous subarea search algorithm based on DIC matching corrected by epipolar constraint is studied,the stereovision 3D displacement measurement software is complied based on MATLAB,and the experiments are conducted in lab to verify the effectiveness and reliability of the proposed stereovision methods.The main contents of this paper are given as follows.Firstly,a 3D displacement measurement method based on two coordinate systems is proposed in this paper.The method requires the straight line determined by the optical centers of the two cameras is parallel to the surface of the object measured.The binocular stereovision 3D coordinate calculation formula is used to obtain the three-dimensional coordinates of the spatial point in the left camera coordinate system and the right camera coordinate system.Then,the 3D coordinates of the spatial point in the world coordinate system are calculated by using the spatial position relation between the spatial point and the two camera optical centers.Secondly,a stereovision 3D displacement measurement method based on two free laid cameras is proposed in this paper.When the camera observes the object in an arbitrary orientation,make the world coordinate system is built on the left camera.Then the transformation matrix between the left camera coordinate system and the world coordinate system is built by means of a calibration plate.Next the binocular stereovision 3D coordinate calculation formula is operated to obtain the 3D coordinates of the spatial point in the left camera coordinate system.Finally,the calculated 3D coordinates are transformated by the rotation matrix of the transformation matrix to obtain the 3D coordinates of the spatial point in the world coordinate system.Thirdly,a synchronization subarea search algorithm with corrected epipolar constraint of DIC matching is proposed.The DIC matching is performed on all the points on the left initial image and the right initial images to obtain the corresponding coordinates of all measurement points in the left and right images.Then,use the pole line constraint to correct the DIC match result of all the points on the right image,i.e.,take the point on the right pole line closest to the DIC match point as the new match point.After this,DIC timing matching is performed on all the points on the subsequent left and right image sequences.All the measurement points in each picture are matched to the next picture in turn in the DIC timing matching.The range of matching is the respective subarea of each measurement point.On the basis of the above-mentioned stereovision measurement algorithms and the synchronization subarea search algorithm,a stereovision 3D displacement measurement software is compiled in this paper.Finally,this paper conducts the hysteretic behavior test of steel plate shear wall and obtain dimensional displacement curve of steel plate shear wall.By comparing the displacement measurement results of stereovision method with the results of LVDT,it verifies the validity of stereovision 3D displacement measurement method based on two coordinate systems.Besides,this paper conducts the shaking table test of a building of Xuan Kou middle school in Yingxiu Town,Wenchuan County and obtains the displacement-time curves in three directions of the frame model under the action of 1000 gal unidirectional Wenchuan main vibration and two-way Wenchuan main vibration(800gal and 700gal).The test results show the displacement data measured by the stereovision 3D displacement measurement method based on two free laid cameras.The measured data is in good agreement with the data measured by the displacement sensors,which verifie s the validity of the stereovision 3D displacement measurement method based on two free laid cameras.