Tangent space(切线空间)

https://en.wikipedia.org/wiki/Frenet%E2%80%93Serret_formulas

The tangent, normal, and binormal unit vectors, often called T, N, and B, or collectively the Frenet–Serret frame or TNB frame, together form an orthonormal basis spanning ℝ³ and are defined as follows:

• T is the unit vector tangent to the curve, pointing in the direction of motion.
• N is the normal unit vector, the derivative of T with respect to the arclength parameter of the curve, divided by its length.
• B is the binormal unit vector, the cross product of T and N.

切线空间中的T（tangent），B（Bitangent）与贴图U，V方向一致。 保存方式（T,B,N）

Normal 

T（tangent）

 B（Bitangent）  = N*T