... > 0 tE, >: E,), < 0 IE, r E~), > o E6 JV3 (E, Y E,), > 0 (E6 >. E,), . 0 ''2 Figure 6- 14 Identifying a concave polygon by calculating cross ... X Es = (0,0, -2) E3 x E4 = (0,O. 2), E, X E5 = (0,0 ,6) E5 x E, = (0,0 ,6) . E, x E, = (O,O, 2) Figure 6- 15 Since the cross product Ez X E3 has a negative 2 component, ... 0) + y, sin 6 + t, 8 y,(l - cos 0) - x, sin 6 + t, 1 I Here, orthogonal unit vectors in the upper-left 2-by-2 submatrix are (cos 0, -sin %) and (sin 0, cos 6) , and Similarly,...