## 1 Introduction
According to the geometry of large-scale conical workpieces, integrating three-dimensional laser scanning and virtual environments, a novel rapid on-machine geometric measurement system was presented, and the 3D scanner is used to obtain the critical contour of the workpiece surface at high speed [17]. [PERSON] and [PERSON] et al. [18] discussed different non-contact 3D measuring strategies and presented a model for measuring geometrically complex parts, manipulated through a robot arm, using a novel vision system which consists a laser triangulation sensor and a motorized linear stage. However, the application of 3D scanners for large-scale workpiece inspection, such as high-speed railway track slabs, is relatively rare. With an increasing amount of research--by institutes, units, and scholars--on high-precision track slab detection technology, many important theoretical achievements and patents have been attained. [PERSON] et al. [1] investigated a photogrammetric method to detect the track slab. The method adopts the marking point and the base station ruler on the track slab. It uses a digital camera to take a picture, and then uses the image matching principle to realize the registration between the image pairs and extracts the three-dimensional coordinates of each key position to calculate each detection indicators. The method requires the inspection tooling to perform the matching measurement, which can meet the requirements of rapid measurement on site. [PERSON] et al. [19] introduced the concept of industrial digital photogrammetry in the detection of CRTS III track slab. The system is used as follows the track slab is laid flat, the code control bracket is placed on the track slab to be detected, and the measuring device is erected thereon, so that the laser points of the guiding device are all projected onto the key position of the supporting block, and controlled. The camera motion completes the data acquisition of the whole slab, and finally extracts all the detection indicators by using feature extraction and calculation methods based on image features. [PERSON] et al. (2019) reported a linear detection system for the track slab rapid detection system based on the three-dimensional detection technology of line image technology. The high-precision measurement reference platform and fast-moving mechanism are used to realize the plane image and 3D model size extraction of the track slab, and the key geometry of the track slab is obtained by algorithm correction. [PERSON] et al. (2019) investigated a CRTS III track slab detection method based on laser tracking and handheld laser scanning combination. The method uses a hand-held laser scanner to scan the track slab in all directions, and the laser tracker achieves the real-time position and posture of the scanner to complete the stitching of the point cloud data. In this cycle, the point cloud data acquisition of the entire track slab surface is completed. Finally, the point cloud classification algorithm is used to classify different feature planes, thereby extracting the detection indexes of the track slab. When this detection method is used to detect the relative dimensional deviation of the track slab embedded bushing, it needs to rely on the spherical self-centralizing tooling, so the automatic detection cannot be completely realized. When the detection method detects the dimensional deviation of the pre-embedded casing of the track slab, it is necessary to use the spherical self-centering tooling, and the automatic detection cannot be fully realized. [PERSON] et al. (2019) discussed the application of 3D laser scanning technology in the detection of CRTS III track slab. A large amount of point cloud data on the track slab surface is used for 3D reconstruction of the target, and the target geometric data is quickly obtained by the reconstructed model library. Finally, the target geometric data is compared with the BIM model to determine the construction deviation accurately.