TVector3 v1u=v1.Unit();
TVector3 v2u=v2.Unit();

// first vector on plane
plo[0]=v1u.X(); 
plo[1]=v1u.Y();
plo[2]=v1u.Z();
// second vector on plane
plo[3]=v2u.X();
plo[4]=v2u.Y();
plo[5]=v2u.Z();
// origin of the plane 
plo[6]=v0.X();
plo[7]=v0.Y();
plo[8]=v0.Z();

// normal to the plane (the third vector to define the reference system u, v, w)
TVector3 v3=v1u.Cross(v2u); 
plo[9]=v3(0);
plo[10]=v3(1);
plo[11]=v3(2);