When the projections of two points in space on a projection plane coincide, these two points are called projection planes, and the projections of invisible points need to be added. When the projection of two points in space on the projection plane coincides with a point, they are called ghost points on the projection plane. When judging the visibility of ghost points, we need to pay attention to the projection of shadow points on another projection plane. Point projections with large coordinate values are visible, and vice versa. Projections of invisible points are indicated by brackets.