https://www.sciencedirect.com/science/article/pii/S1077314214000824 (Publisher version)
Ahmad, A., Xavier, J., Santos-Victor, J., & Lima, P. (2014). 3D to 2D bijection for spherical objects under equidistant fisheye projection. Computer Vision and Image Understanding, 124, 172-183. doi:10.1016/j.cviu.2014.04.004.