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Dual conic

Similarly, the dual concept exists for lines. A conic envelope or dual conic is the locus of all lines ${\tt l}$ satisfying a homogeneous quadratic equation:
{\tt l}^\top {\bf C}^* {\tt l} = 0 \, ,
\end{displaymath} (B11)

where ${\bf C}^*$ is a $3 \times 3$ symmetric matrix only defined up to scale. A dual conic thus also depends on five independent parameters.

Marc Pollefeys 2002-11-22