1. Anglin, W.S.: Using Pythagorean triangles to approximate angles. Am. Math. Mon. 95(6), 540–541 (1988)
2. Fredriksson, K.: Rotation Invariant Template Matching. Ph.D. thesis, University of Helsinki (2001)
3. Galarza, A.I.R., Seade, J.: Introduction to Classical Geometries. Birkhäuser, Cambridge (2007)
4. Hunter, D.J.: Essentials of Discrete Mathematics, 2nd edn. Jones & Bartlett Learning, Burlington (2010)
5. Jacob, M.A., Andres, E.: On discrete rotations. In: 5th International Workshop on Discrete Geometry for Computer Imagery, pp. 161–174 (1995)