ices contained in the segment is:

                     vrtces[0][0]      segment_vertex_set[start][0]
                     vrtces[0][1]      segment_vertex_set[start][1]
                     vrtces[0][2]      segment_vertex_set[start][2]
                       ...             ... 
                     vrtces[n-1][0]    segment_vertex_set[start+n-1][0]
                     vrtces[n-1][1]    segment_vertex_set[start+n-1][1] 
                     vrtces[n-1][2]    segment_vertex_set[start+n-1][2] 
           