The product appearance data (point cloud) scanned by the 3D scanner will have some inevitable introduction error data, especially the measurement data near the boundary and the sharp edge with more difficulty and more dead angles, and the measurement data is bad. Point, which may make the point and its surrounding patches off the original surface so that the data is not accurate enough, so the original point cloud data should be preprocessed, usually through the following steps:

1. Data interpolation. For some areas that are not scanned by 3D scanners, the data can only be filled by data interpolation. Here we should consider two kinds of surface modeling techniques, and the surface-reverse modeling based on point-spline And point-based surface fitting techniques.

2, the data is smooth, the purpose of data smoothing is to eliminate the noise point, get accurate model and good feature extraction effect, using the smoothing method, stress to keep the information that the parameters can be obtained unchanged.

3, remove the noise point, the commonly used inspection method is to display the point cloud on the graphic terminal, or generate curved surface, use the semi-interactive semi-automatic smoothing method to check and adjust the point cloud data.

4, the data is smooth, smooth refers to smooth, pleasing to the eye, but due to the accuracy requirements, it is not allowed to apply excessive modification to the measured data points to meet the smoothing requirements, on the other hand due to the diversity of physical boundary surfaces Certain feature points on the boundary must be preserved and cannot be considered 'bad points.'

5. The relocation and integration of the point cloud, the data formed by multiple scans after re-stacking should be relocated and integrated. Currently, the general CAD software does not have this function. It needs manual processing by the styling personnel, and selects two on the measuring part. In the sub-positioning state, in the process of two positioning measurements, the coordinate values of the reference points in the two positioning states are respectively measured, and then the measurement accuracy of each reference point is determined by a certain judgment rule, and finally in the CAD system. The measurement data under the positioning is displayed, and the data under one positioning is moved, so that all the measurement data under the positioning is integrated into another positioning.