Four-point-algorithm for the recovery of the pose of a one-dimensional camera with unknown focal length

The authors give an algorithm for recovering the centre and view direction of a one-dimensional camera with known principal point but unknown focal distance, by means of one view with four recognised landmarks. The involved algebra is reduced to solving a quadratic equation. This 4-point-method appears to be more robust than the existing 5-point-algorithm for locating a totally uncalibrated camera by means of chasles conics. On the other hand, the authors´ method can offer an alternative for the triangulation method if the value of the focal length is unknown or unreliable (e.g. because of autozoom).