1. A method of registering normal maps, comprising the steps of: converting observed object data to an observed normal map; calculating a 3-D rotation matrix for a first normal map and a second normal map; producing 2-D planar transform weights by warping a 2-D position of surface normals of at least one of the observed normal map and each reference normal map in an image plane; and jointly optimizing the 3-D rotation matrix and the 2-D planar transform weights of the first and second normal maps until convergence to a registered normal map pair.