paella/report/subsections/calibration.tex

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% 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.