3-D pose from 3 points using weak-perspective

This correspondence discusses computing the pose of a model from three matching point pairs under weak-perspective projection. A new approach to the problem that is motivated geometrically is described. Like previous methods, the method here involves solving a biquadratic equation, but here the biquadratic´s solutions, comprised of an actual and a false solution, are interpreted graphically. The final equations take a new form, which leads to a simple expression for the image position of any unmatched model point