The unique solution of projective invariants of six points from four uncalibrated images

In this paper, we show that four uncalibrated images are sufficient to uniquely determine the 3D projective invariants of a set of six points in general position in space. An algorithm for computing the unique solution is proposed. It computes by solving a set of linear equations for its two linear independent solutions and is simpler than other algorithms which compute the three possible solutions of 3D projective invariants by solving a set of nonlinear equations. However, a fourth image is needed to get the linear unique solution. Finally, experimental results have shown the feasibility of this algorithm.