Illustration of the graph construction procedure. Each loop starts with Step 1 and ends at Step 4. In the graph, the nodes (i.e., “a”–“i”) denote the skeleton points, the edges between nodes represent the distance between the skeleton points. In this example, let “a” be the randomly selected point, then other skeleton points are added to the voxel set in the following sequence: “bcde | fgh | i |”, where “|” means Step 4 is called.
