The projection of an object cannot be used to represent a space object in engineering.

In engineering, the projection of objects can be used to represent space objects, and center projection and parallel projection methods are commonly used.

Central projection:

central projection

Central projection refers to the projection formed by light scattering from a point. It is a projection method of aerial photography. It refers to the perspective relationship formed when any straight line in space is projected onto a plane (shadow plane) through a fixed point (projection center). It is characterized in that the light reflected by each object point is focused on the photosensitive film through the lens; Moreover, the focus of each ray and negative film is to form a negative image on the negative film, which becomes a positive image after printing. Central projection has imaging law, also called perspective law.

Parallel projection method:

If the projection center of the central projection, that is, the light source S, is moved to infinity, the projection lines will become mutually parallel straight lines, and the object projection will not be affected by the distance change. This projection method with parallel projection lines is called parallel projection method. Parallel projection method can be divided into orthographic projection method and oblique projection method according to the different included angles between projection lines and projection planes.