Viewpoint determination of cylinders and spheres from a single view

The ellipse projected from a circle or a sphere in 3D can be used to recover the position of the circle or the sphere, if the model radius is known. A closed-form solution for the 3D position and orientation of a circular feature and the 3D position of a spherical feature is described. There are two general solutions for the circular feature, but there is only one solution when the surface normal of the circular feature passes through the center of projection. This method handles spherical as well as circular features. It has closed-form solutions, and it gives only the necessary number of solutions (no redundant solutions)