在第一条直线上可以得到多个点，在第二条直线上也可以得到多个点，因此就可以得到再用一束线激光投射到棋盘格的相纸靶标上，重复上面的方法，便可以得到第三个交点（xc3，yc3，zc3），把这三个点代入光刀平面方程(Multiple points can be obtained on the first straight line, and multiple points can also be obtained on the second straight line. Therefore, a laser beam projected onto a checkered photographic paper target can be obtained, and the above method can be repeated. Then we can get the third intersection (xc3, yc3, zc3), and substitute these three points into the plane equation of the light knife.)