(A-D) test four protein models with 500 sample points each. (A) 1ctr. (B) 1b7t. (C) 1irk. (D) 2btv. Column 1 shows the isosurfaces with the simulated 8 Å resolution density maps for the four models. Column 2 shows the uniform sample points, while column 3 shows the pathes of inner distances. Points on boundary surfaces are colored in gray, sample points are colored in red, and the edges of inner distance are colored in green.