Throughout this article, vectors and matrices are denoted in bold-face.
Especially, 
and 
represent
n-dimensional zero vector and 
identity matrix,
respectively. Symbol 
represents the transposition of vectors or
matrices. Therefore 
is a scalar product of
two vectors, 
and 
. Any vector representing
a homogeneous coordinate of a 2D or 3D point is underlined, e.g.
. For any 3-vector 
, a
3
3 anti-symmetric matrix 
is defined as
