The row vectors of the camera matrix

The row vectors of the projective camera are 4-vectors which have the geometric interpretations as particular world planes. Let us write the rows of the projective camera as ${\bf\pi}_1^T$ , ${\bf\pi}_2^T$ and ${\bf\pi}_3^T$ . That is

$$\tilde{\bf P} = \left[ \begin{array}{l} {\bf\pi}_1^T \\ {\bf\pi}_2^T \\ {\bf\pi}_3^T \end{array} \right]$$