Methods The designed lensometer primarily consists of light system, collimating system and projective system.

In the first, the projective system was given in section two, and the equivalence between linear codes and projective was proofed. So we can use geometric language to describe linear codes.

This paper presents a method of arc projective transformation of the fundamental geometric elements on a sphere, and sets up an are projective system for three axial and two axial correspondently.