Finished approach and align

documentation/align.tex

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+\section{Goal Alignment}
+
+After the approach, described in the section \ref{p sec approach}, is finished,
+the robot is facing the ball, and the ball is at a short distance. In the stage
+of goal alignment, the task is to ensure that from the robot's point of view
+the ball lies between the goalposts. This means, that when the robot is
+centered at the ball, the goalposts should lie on either side of the center of
+the camera image. So the robot will first detect the goal and determine if that
+is the case. If that is not the case, the robot will go around the ball in a
+circle in the appropriate direction, until the ball is indeed between the
+goalposts.
+
+The walk in circle was implemented in the following way: the robot will step
+several steps sideways, then will turn to ball, as described in the section
+\ref{j sec turn to ball}, and finally will adjust the distance to the ball by
+stepping forwards or backwards, so that the ball is neither too close nor too
+far. The distance to the ball, similarly to the stage of the direct approach,
+is not measured explicitly, but is approximated through the position of the
+ball image in the camera frame. After performing these steps, the check is
+performed, if the goal alignment is completed. Otherwise, the steps will be
+repeated until alignment is achieved.
+
+\begin{figure}[ht]
+  \includegraphics[width=\textwidth]{\fig goal-alignment}
+  \caption{Successful goal alignment}
+  \label{p figure goal-alignment}
+\end{figure}
+
+\section{Ball alignment}
+
+Now that the ball and the goal are aligned, the robot has to move to the ball
+into a position, from which the kick can be performed. Depending on the
+situation, it may be feasible to select the foot, with which the kick should be
+performed, but due to time constraints we programmed the robot to kick with the
+left foot only. So, the task now is to place the ball in front of the left
+foot. We realized, that when the ball is in the correct position, then its
+image in the lower camera should be within a certain region. We experimentally
+determined the extents of this region. The algorithm therefore is for the robot
+to gradually adjust its position in small steps, until the ball image reaches
+the target, after which the robot will proceed with the kick. Our tests have
+shown, that this approach while being relatively simple, works sufficiently
+robust, which means that we didn't have the situations, when the robot missed
+the ball after alignment or even hit the ball with an edge of the foot.
+
+\begin{figure}[ht]
+  \includegraphics[width=\textwidth]{\fig ball-align}
+  \caption{Ball alignment}
+  \label{p figure ball-alignment}
+\end{figure}