File:Back-observation-quadrant.svg

% !Mode:: "TeX:UTF-8"
\documentclass[tikz]{standalone}
\usetikzlibrary{positioning}
\usetikzlibrary{calc}

\begin{document}
	\footnotesize
	\begin{tikzpicture}
		[
			sight/.style={densely dashed,red},
			vane/.style={color=blue}
		]
		\draw (0,0) -- (5,0) arc [start angle=0,end angle=90,radius=5] (0,5) -- (0,0);
		\draw (4.5,0) arc [start angle=0,end angle=90,radius=4.5] (0,4.5);
		\foreach \x in {5,15,...,85} \draw (\x:4.9) -- (\x:5);
		\foreach \x in {10,20,...,80} \draw (\x:4.85) -- (\x:5);
		\draw [sight] (-1,0) -- (6,0);
		\draw [sight] (0,0) -- (59:6);
		\fill [vane,rotate around=-31:(59:5)] (59:5) rectangle +(-0.5,0.1);
		\node [vane] at (59:5) [above left=0.3cm and 0.2cm] {A};
		\fill [vane,rotate=-50] (-0.3,-0.1) rectangle (0.3,0.1);
		\node [vane] at (0.3,-0.2) [right] {B};
		\fill [vane] (3.9,-0.3) rectangle (4.1,0.3);
		\node [vane] at (4.1,-0.3) [right] {C};
		\draw [shorten >=-0.1cm] (7,0) to [bend right=20] (6.5,-0.2);
		\draw [shorten >=-0.1cm] (7,0) to [bend left=20] (6.5,0.2);
		\draw [clip] (7,0) to [bend right=20] (6.5,-0.2) to [bend left=10] (6.5,0.2) to [bend right=20] (7,0);
		\fill [vane] (6,0) circle [radius=0.55];
	\end{tikzpicture}
\end{document}