Notation for plane (i.e. 2D) projective geometry. NB ``='' means equality up to scale.
where and
are
the inhomogeneous plane coordinates. Only the
ratio of the homogeneous coordinates is
significant.
for the line .
Again, only the ratio of the homogeneous line coordinates is
significant.
where
is a
skew-symmetric matrix of rank
2.
is the one dimensional kernel of
,
since
.