[Tex/LaTex] Best way to denote an angle in TikZ

tikz-pgf

What is the best and simplest way to denote an angle, with an arc and a label telling its name? I wish to be able to control (obviously) the vertices on which the angle lays, the name of the angle and also control the radius of the little arc and whether it should fill the whole part-of-a-circle shape in color.

Best Answer

I just have a look to this question and related ones but I don't see anywhere my solution to mark an angle when you don't know its measure (maybe I haven't read all the post about the topic...).

So here it is:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
\coordinate[label=below left:$A$] (A) at (0,0);
\coordinate[label=below right:$x$] (X) at (6,1);
\coordinate[label=above left:$y$] (Y) at (3,5);

\draw[thick] (X) -- (A) -- (Y);

% Mark the angle XAY
\begin{scope}
\path[clip] (A) -- (X) -- (Y);
\fill[red, opacity=0.5, draw=black] (A) circle (5mm);
\node at ($(A)+(30:7mm)$) {$\theta$};
\end{scope}

\end{tikzpicture}

\end{document}

I draw a full circle and I hide the bad part of it by clipping with a path built with the three points which define the angle. It seems so easy that it might be a bad way to do it but it works pretty well. Here I put manually the angle measure to place \theta but it could be automated surely.

Please, feel free to comment it if you think there are some situations where it doesn't work!

Mark an angle

Related Solutions

[Tex/LaTex] How to automatically obtain the center of the circle used to draw the arc in TikZ

Only part of what was required. But it also shows how a key with the required syntax could be programmed:

\documentclass[tikz,border=5]{standalone}
\tikzset{%
insert arc/.style args={#1:#2:#3and#4 with center #5}{
  insert path={
    \pgfextra{%
      \pgfpointxy{#3}{#4}%
      \pgfgetlastxy\arcrx\arcry%
      \pgfcoordinate{#5}{%
        \pgfpoint{\csname tikz@lastx\endcsname+\arcrx*cos(#1+180)}%
          {\csname tikz@lasty\endcsname+\arcry*sin(#1+180)}}
      }
    arc (#1:#2:#3 and #4) 
    }
  }
}

\begin{document}
\begin{tikzpicture}[rotate=40]
\draw [very thick] (0,0)  [insert arc={-25:45:3 and 2 with center X}];

\draw [dashed, red] (X) ellipse [x radius=3, y radius=2];
\end{tikzpicture}
\end{document}

enter image description here

And a slightly more comprehensive example:

\begin{tikzpicture}
\draw [very thick] (0,0) -- (0,1)  
  [insert arc={270:135:3 and 2 with center X}] -- (-4,4) 
  [insert arc={ 10:-90:1 and 3 with center Y}]
  [insert arc={180:360:4 and 2 with center Z}] -- cycle;

\draw [dashed, red]   (X) ellipse [x radius=3, y radius=2];
\draw [dashed, green] (Y) ellipse [x radius=1, y radius=3];
\draw [dashed, blue]  (Z) ellipse [x radius=4, y radius=2];
\end{tikzpicture}

enter image description here

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

A solution which allows to draw intersection segments of any two intersections is available as tikz library fillbetween.

This library works as general purpose tikz library, but it is shipped with pgfplots and you need to load pgfplots in order to make it work:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}];

\end{tikzpicture}

\end{document}

enter image description here

The key intersection segments is described in all detail in the pgfplots reference manual section "5.6.6 Intersection Segment Recombination"; the key idea in this case is to

create a temporary path temp1 which is the first intersection segment of red and blue, more precisely, it is the first intersection segment in the Left argument in red and blue : red. This path is drawn as thin black path. Substitute its \draw statement by \path to make it invisible.
Compute the desired intersection segment by intersecting temp1 and green and use the correct intersection segment. By trial and error I figured that it is the third segment of path temp1 which is written as L3 (L = left argument in temp1 and green and 3 means third segment of that path).

The argument involves some trial and error because fillbetween is unaware of the fact that end and startpoint are connected -- and we as end users do not see start and end point.

Note that you can connect these path segments with other paths. If such an intersection segment should be the continuation of another path, use -- as before the first argument in sequence. This allows to fill paths segments:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,fill=blue,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}]  
    [intersection segments={of=temp1 and green, sequence={--R2}}]
;

\end{tikzpicture}

\end{document}

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] How to automatically obtain the center of the circle used to draw the arc in TikZ

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

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