Accurate Measurement and Evaluation Methodology of Vehicle-Body Symmetry Plane Verified by Absolute Benchmark

Accurate measurement of symmetry plane is very important to the research field of industrial detection. A solution model of the symmetry plane of vehicle body is constructed by the improved expectation–maximization (IEM) method. The coarse-to-fine process and the
$M$
-neighborhood method are developed to achieve the parallel computing process and enhance the detection efficiency, according to the vehicle point cloud. In order to verify the measurement accuracy, a 3-D point-cloud dataset is established with different vehicle bodies. As the vehicle bodies in the dataset derive from program models, the symmetry plane is known in the modeling process. An evaluation method with the projection angles for the vehicle-body symmetry plane is described for the wheel alignment measurement benchmark. The method is further compared with other methods, on the basis of the vehicle dataset and evaluation indicators. Moreover, the physical, absolute benchmark of the symmetry plane, which is generated from the high-precision rotation table of the verification instrument, conducts the experimental verification of the solution method of the symmetry plane.