Example: Polar plot with grid

Published 2014-05-19 | Author: Alex Chan

The grid is drawn by hand and with some basic loops, such as concentric circles and labels in a foreach loop. The shaded area got opacity so we can see through.

This example was written by Alex Chan answering a question on TeX.SE.

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\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}[>=latex]

% Draw the lines at multiples of pi/12
\foreach \ang in {0,...,31} {
  \draw [lightgray] (0,0) -- (\ang * 180 / 16:4);
}

% Concentric circles and radius labels
\foreach \s in {0, 1, 2, 3} {
  \draw [lightgray] (0,0) circle (\s + 0.5);
  \draw (0,0) circle (\s);
  \node [fill=white] at (\s, 0) [below] {\scriptsize $\s$};
}

% Add the labels at multiples of pi/4
\foreach \ang/\lab/\dir in {
  0/0/right,
  1/{\pi/4}/{above right},
  2/{\pi/2}/above,
  3/{3\pi/4}/{above left},
  4/{\pi}/left,
  5/{5\pi/4}/{below left},
  7/{7\pi/4}/{below right},
  6/{3\pi/2}/below} {
  \draw (0,0) -- (\ang * 180 / 4:4.1);
  \node [fill=white] at (\ang * 180 / 4:4.2) [\dir] {\scriptsize $\lab$};
}

% The double-lined circle around the whole diagram
\draw [style=double] (0,0) circle (4);

\fill [fill=red!50!black, opacity=0.5] plot [domain=-pi/2:pi/2]
  (xy polar cs:angle=\x r, radius= {2-2*sin(\x r)});
\draw [thick, color=red, domain=0:2*pi, samples=200, smooth]
  plot (xy polar cs:angle=\x r, radius={2-2*sin(\x r)});
\node [fill=white] at (2,1) {$r=2-2\sin\theta$};

\end{tikzpicture} 
\end{document}