How to set the normal vector of the coordinate plane? For example, what are the normal vectors of the space coordinate system XYZ, xoy plane (there should be two zeros)

How to set the normal vector of the coordinate plane? For example, what are the normal vectors of the space coordinate system XYZ, xoy plane (there should be two zeros)

The normal vector of xoy plane is [0,0,1]. In three-dimensional space, the equation of plane is a * x + b * y + C * Z + D = 0 (a ^ 2 + B ^ 2 + C ^ 2 is not equal to zero). It is the generalization of plane linear equation a * x + b * y + C = 0 (a ^ 2 + B ^ 2 is not equal to zero), and its normal vector is [a, B, C]. The coordinates of points on the plane satisfy the equation. Because the equation of xoy plane is Z = 0, that is a = 0, B = 0
, C = 1, d = 0, so its plane normal vector is [0,0,1]