Hi, Let's think about 4 points A,B,C,D. I need to locate the points in 3D Cartesian coordinates provided the following parameters are given about the point: 1] Distance between A and B. 2] Distance between B and C 3] The angle between A B and C. 4] The angle between B C and D. 5] The torsion angle A-B-C-D. I want to program this up so that in my simulation I can attach atoms to each other provided the bond-lengths, bond angles and torsion angles are specified. I need help with the math. We know that we must start by setting up the coordinate system. So for the first set of 4 atoms, we can place A at the origin, B along any of the coordinate axes and finally C in a chosen plane. But once we are through with the first set, what is a general formulation for the solution of the problem ? Please let me know if you know of any books/articles which deal with similar issues. Thanks for your help.