| 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 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 p = l1 l2 |
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| Points and lines
are dual in projective space |
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| • | given any
formula, can switch the meanings of points and |
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| lines to get
another formula |
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