基于Open3D的点云处理8-点云切片

点云切片，即用一组平面与点云相交，切出满去要求的点云，如下测试用例，用两个平面切出平面之间的点云。

import open3d as o3d
import  numpy as np
#给定三个空间点，计算平面表达式Ax+By+Cz+D=0
def computePlane(a,b,c):
        x1 = a[0]
        x2 = b[0]
        x3 = c[0]
        y1 = a[1]
        y2 = b[1]
        y3 = c[1]
        z1 = a[2]
        z2 = b[2]
        z3 = c[2]
        A = y1 * (z2 - z3) + y2 * (z3 - z1) + y3 * (z1 - z2)
        B = z1 * (x2 - x3) + z2 * (x3 - x1) + z3 * (x1 - x2)
        C = x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)
        D = -(x1*(y2*z3 - y3 * z2) + x2 * (y3*z1 - y1 * z3) + x3 * (y1*z2 - y2 * z1))
        return [A,B,C,D]
if __name__ == '__main__':
   ply=o3d.io.read_point_cloud("./data/test.ply")
   #点个数
   num_points = len(ply.points)
   #计算平面参数
   A,B,C,D = computePlane(ply.points[460245], ply.points[443601], ply.points[449575])
   #两个平面
   d1=D+0.1
   d2=D-0.1
   idx=[]
   for i,point in enumerate(ply.points):
       #处在两个平面之间 (Ax+By+Cz+D1)  *   （Ax+By+Cz+D2）  <    0
        if (A*point[0]+B*point[1]+C*point[2]+d1)*(A*point[0]+B*point[1]+C*point[2]+d2)<0:#符号相反
                idx.append(i)
   #提取切片的点
   slice= ply.select_by_index(idx)
   slice.paint_uniform_color([1,0,0])
   #提取剩余的点
   rest_points= ply.select_by_index(idx,invert=True)
   rest_points.paint_uniform_color([0,0,1])
   o3d.visualization.draw_geometries([slice])
   o3d.visualization.draw_geometries([slice,rest_points])