I. Introduction
Body shop is one of the most important workshops in the production line of automobiles. In body shop, hundreds of mechanical components are required to be placed and welded in the right positions of each vehicle, the accuracy of which greatly affects the quality and performance of the produced cars. It has been reported that more than 30% of quality defects of a car come from the dimensional deviation of body in white in the assembly process [1]. Low assembly quality will further lead to various problems in the car's service cycle, such as wind noise, water leakage, door closing problems, which cause large service and repair costs. Therefore, dimension control is an essential task of body assembly for ensuring and improving the quality of the produced cars.