Figure 1
From: Protein-protein binding site identification by enumerating the configurations

Steps to obtain a transformation. (1) put a i at one of the grid points d-ball of b i′ . (2) put a j at a grid point on the intersection of the sphere centered at a i with radius |a i a j | and d-ball of b j′ . There are at most grid points on the intersection. (3) use a i and a j as the rotation axis.