A Simple Procedure to Solve Motion and Structure from Three Orthographic Views

In his influenlial work on motion analysis [1], Ullman showed that for the orthographic case, 4-point correspondences over three views are sufficient to determine motion and structure of the 4-point rigid configuration. However, his method is nonlinear and the conditions of uniqueness and convergence of his algorithm are not made clear. In this communication, we show a very simple linear algorithm to solve Ullman's problem of determining motion and structure from three orthographic views. We also give necessary and sufficient conditions of a unique solution. This research paves the way towards a robust version of the algorithm which, as a viable and practical means for computing structure and motion, may have a potential for wide applications.