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Marion Lenfant 2015-03-12 17:31:06 +01:00
commit a1860c39f0
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\part{First part : segmentation, camera calibration, skeletonization, detection and matching of keypoints}
\chapter{Segmentation}
\chapter{Calibration}
\section{Internal calibration}
\section{External calibration}
To test the external calibration, the idea is to have two pictures of a scene
containing two chessboards : one blue and one red. We will compute the
homography that transforms the blue chessboard on the first picture to the blue
chessboard of the second picture. Then, we will apply this transformation to
the red chessboard on the first picture, and if the calibration has a good
quality, the points found should be on the red chessboard.
\begin{figure}[H]
\centering
\includegraphics[scale=0.45]{images/externalCalibration/result.png}
\caption{Test of the external calibration}
\end{figure}
As you can see, the points computed are slightly displaced from the corners of
the chessboard. We can explain this by the difficulty we had to have a very
plane chessboard : the ink from the printer humidify the paper, and we were not
able to have a really plane chessboard.
\chapter{Detection and matching of keypoints}
\section{Detection of keypoints}

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\paragraph{Characteristic circles computation}
We take a point sampled on the spline. It gives us information about the sphere located on this point : C(t) the sphere center coordinates and r(t) its radius. We also have their derivatives : C'(t) and r'(t). The idea is to find the intersection between this sphere and the characteristic plane, which would give us the characteristic circle.
If a point P is on the circle, then we can write this formula :
$<C'(t),PC(t)> - r'(t)r(t) = 0$
and then we calculate the center of the characteristic circle with this formula :
$Cp(t) = C(t) r'(t)r(t)/norm(C'(t))² * C'(t)$
\begin{figure}[H]
\begin{center}
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After obtaining characteristic circles we sample them. Then we need to find matching points. We decided to make points sampling start in one direction of our mark. When this is done we project the mark on the new circle and sample again. Then we link each point to the point of the same index on the next circle.
$TODO$
%TODO