% Here we go
\subsection{Camera calibration}
    The camera calibration is needed by the client during the reconstruction of the 3D skeleton. The calibration consists in two steps :

    \begin{enumerate}
        \item the \textbf{internal calibration} which is the estimation of the instrinsic parameters of the camera (such as the focal length, or the
        principal point)

        \item the \textbf{external calibration} which is the estimation of the
        extrinsic parameters (the position of the camera from the chessboard)
    \end{enumerate}

    \subsubsection{Internal calibration}
        The internal calibration is based on a program that we completed during a lesson last semester. By detecting chessboards from numerous positions of the camera, we are able to estimate the intrinsic parameters. This program takes as input a video of a chessboard where the camera position changes, and it captures some frames on which the chessboard is detected. With these pictures, we estimate the intrinsic parameters.

    \subsubsection{External calibration}
        For the external calibration, we wrote a program that uses an
        estimation of the homography to compute the extrinsical parameters of
        the camera. One should note that what we call the \emph{extrinsical
        parameters} are the ones that convert points from the reference of the
        chessboard to the reference of the camera.