To obtain a unique solution, we need to add a 4th point. One straightforward approach is to take subsets of 3 of the 4 points, solve the 4th degree polynomial equation for each subset and finally find the common solution. This is indeed the most frequent practice both in photogrammetry and computer vision. However there are several drawbacks. The first is that we have to solve several 4th degree polynomials. Secondly, we need to find the common solution which might be difficult due to noisy data. Finally, and probably the most important, we can not profit from the redundancy of the data which should increase stability.