Figure 2

Two-dimensional illustration of the scheme for the algorithm. (A) Volumetric representation of protein. The solid dots denote the set of protein data placed on the uniform grids. The grids without solid dots are outside of the protein. (B) The boundary contour of the protein. The region highlighted by a red square is used for the illusion of normal calculation. (C) The figure zooms in the highlighted region in (B) to illustrate the calculation of the normal. The center point is one of the boundary points and three open dots are defined as its visible points. The three green arrows denote the visible direction vectors. The normal is the vector summation of D₁, D₂ and D₃. (D) The visualization of ray intersection. A virtual cone (colored orange) with P₂ as vertices is shown in the figure. A ray (colored orange) shot from point P₁ and the corresponding virtual cylinder (colored blue) around the ray are shown. There are three circles (colored purple) describing the different clusters of intersection points respectively.