| Point and line duality |
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| • | A line l
is a homogeneous 3-vector |
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| • | It is ^ to every point (ray) p
on the line: l p=0 |
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| p2 |
| l1 |
| p |
| p1 |
| l |
| l2 |
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| What is the line l
spanned by rays p1 and p2 ? |
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| • | l is
^ to p1
and p2 Þ l = p1 ´ p2 |
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| • | l is the
plane normal |
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| What is the
intersection of two lines l1 and l2
? |
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| • | p is
^ to l1
and l2 Þ p = l1 ´ l2 |
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| Points and lines
are dual in projective space |
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| • | every property of
points also applies to lines |
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