1. Introduction
As 3D data acquisition techniques develop rapidly, different types of 3D scanners, e.g. LiDAR scanners [22] and RGB-D cameras [10] are becoming popular in our daily life. Basically, 3D scanners can capture data that enables AI-driven machines to better see and recognize the world. As a fundamental data representation, point clouds can be easily collected using 3D scanners, retaining abundant information for further investigation. Therefore, point cloud analysis is playing an essential role in 3D computer vision.