* Class for representing a direct local frame composed of 3 orthonormal vectors T (tangent), B (bitangent) and N (normal).
* This class can compress/decompress a local frame, switching from its explicit representation (3 vectors) to its compressed representation (1 vector).
* Usage :
* VEC3 T,B,N ; // current set of orthonormal vectors composing the direct frame.
* LocalFrame<PFP::VEC3> lf(T,B,N) ; // Constructor from explicit expression.
* if (lf.isOrthoNormalDirect()) // test if the frame is Orthogonal, Normalized and Direct