l
Point and line duality
•A
line l is a homogeneous 3-vector
•It
is ^ to every
point (ray) p on the line: l p=0
p1
p2
What is the
intersection of two lines l1 and l2 ?
•p
is ^
to l1 and l2 Þ
p = l1 ´ l2
Points and
lines are dual in projective space
•given
any formula, can switch the meanings of points and lines to get another formula
l1
l2
p
What is the
line l spanned by rays p1 and p2 ?
•l
is ^
to p1 and p2 Þ
l = p1 ´ p2
•l is the plane normal