* 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).

* Two different compressions coexist : one which is not correct on the extreme values (VEC3 getCompressed()) and one which is totally correct (VEC4 getCompressedSecure()).

* 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.

* LocalFrame<PFP> lf(T,B,N) ; // Constructor from explicit expression.

* if (lf.isOrthoNormalDirect()) // test if the frame is Orthogonal, Normalized and Direct