1. A method to correct for rotational distortions of an image projected from an image projector on a viewing surface without using a test pattern, said method comprising: acquiring an image of a scene containing the viewing surface, using at least one image capture device equipped with an Ultra Wide-Angle (UWA) lens with a field of view of about 180° or larger and having a lens mapping transformation, with a known orientation relative to the image projector; using at least one image processing unit to: identify at least a first pair of parallel lines in the image in the UWA lens space; identify at least a second pair of parallel lines, orthogonal to the at least first pair of parallel lines, in the image in the UWA lens space; obtain coordinates of vanishing points corresponding to the at least first and the at least second pair of parallel lines; compute angles of rotation of the at least one image capture device with respect to a frame of reference, using the coordinates of the vanishing points; construct a correction transformation using the rotational angles and the orientation of the at least one image capture device relative to the image projector; wherein the correction transformation for the rotational angles is independent of a position of lens used to capture the image, and apply the correction transformation to correct for the rotational distortion of the image, wherein the correction transformation does not use a test pattern for correction.