In terms of a unit vector n normal to the barrier, these are equivalently: T = | j t r a n s ⋅ ⋅ n j i n c ⋅ ⋅ n | , R = | j r e f ⋅ ⋅ n j i n c ⋅ ⋅ n | , where the absolute values are required to prevent T and R being negative.