Open3d ISS key points

One 、 brief introduction

ISS Its full name is Intrinsic Shape Signatures, It is a three-dimensional shape descriptor , This descriptor is mainly used to describe the local part of the point cloud / Characteristics of semi local regions , This is convenient for later registration and other processes . The calculation process is mainly divided into two steps ：
1、 First, point based $p$ And its adjacent points to create a local coordinate system , The coordinate axis of the coordinate system is the three eigenvectors of the covariance matrix in the following formula .

2、 Judge whether the point is ISS Characteristic point , See the following formula for the judgment conditions ：