[Tex/LaTex] How to draw a circle using TikZ

tikz-pgf

I want to draw a disc using TikZ whose two halves are of different color.

Best Answer

There are many possibilities to realize this. I implemented a center coordinate, which is a bit more flexible. Explanations as comments:

\begin{tikzpicture}
    % Circle's center
    \coordinate (center) at (2,2);

    % Create a blue filled arc, starting 2 above the center, 
    % with a start angle of 90°, an end angle of 270° and a radius of 2
    \fill[blue] (center) + (0, 2) arc (90:270:2);

    % Create a red filled arc, starting 2 below the center, 
    % with a start angle of 270°, an end angle of 450° and a radius of 2
    \fill[red] (center) + (0, -2) arc (270:450:2);
\end{tikzpicture}

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[Tex/LaTex] tikz draw circle segment

Result

Using calc library and the operators let and in you can compute the radius, initial angle and final angle for the arc from the three points you have (center and two circle points), and use then the computed numbers as part of the path. The following MWE shows how:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\thispagestyle{empty}
\usetikzlibrary{calc}

\begin{tikzpicture}
\coordinate (center) at (3,3);
\coordinate (1) at (0,0);
\coordinate (2) at (5, .5);
\coordinate (3) at ($(center) +(30:2)$);
\coordinate (4) at ($(center) +(70:2)$);
\coordinate (5) at (0,6);

\draw[blue, dotted]
      let \p1 =  ($(3)-(center)$),
          \n0 = {veclen(\x1,\y1)}
      in (center) circle(\n0);


\filldraw[draw=black, fill=green, fill opacity=0.3]
   let \p1 = ($(3) - (center)$),
       \p2 = ($(4) - (center)$),
       \n0 = {veclen(\x1,\y1)},            % Radius
       \n1 = {atan(\y1/\x1)+180*(\x1<0)},  % initial angle
       \n2 = {atan(\y2/\x2)+180*(\x2<0)}   % Final angle
    in
    (1) -- (2) --  (3) arc(\n1:\n2:\n0)  -- (5)  -- cycle;

\foreach \dot in {1,2,3,4,5,center} {
  \fill (\dot) circle(2pt);
  \node[above] at (\dot) {\dot};
}

\end{tikzpicture}
\end{document}

If you have v2.10 of pgf/tikz, you can calculate the initial and final angles using atan2(x,y) instead of the above expression, (thanks to qrrbrbirlbel for suggesting it), i.e:

       \n1 = {atan2(\x1,\y1)},  % initial angle
       \n2 = {atan2(\x2,\y2)}   % Final angle

[Tex/LaTex] Path with complicated colormap in TikZ

pgfplots offers something on these lines. An example from the manual:

\documentclass[border=10pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
\begin{document}
\begin{tikzpicture}
\begin{axis}[axis lines=none]
\addplot[mesh,samples=1000,domain=-4*pi:4*pi,line width=2pt] {sin(deg(x))};
\end{axis}
\end{tikzpicture}
\end{document}

enter image description here

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Related Solutions

[Tex/LaTex] tikz draw circle segment

[Tex/LaTex] Path with complicated colormap in TikZ

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