Binormal Vector

			(1)
			(2)

where the unit tangent vector and unit "principal" normal vector are defined by

			(3)
			(4)

Here, is the radius vector, is the arc length, is the torsion, and is the curvature. The binormal vector satisfies the remarkable identity

(5)

In the field of computer graphics, two orthogonal vectors tangent to a surface are frequently referred to as tangent and binormal vectors. However, for a surface, the two vectors are more properly called tangent and bitangent vectors.