TikZ Angles – Using the Angles Library in TikZ

tikz-anglestikz-pgf

I am trying to use the angles library, but I am not sure how to apply it when the nodes were specified from other methods.

In the examples, the drawing of the vectors and naming of the nodes happens on the same draw command that issue the angles command.

\documentclass[tikz]{standalone}%

\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\usetikzlibrary{angles}

\begin{document}
\begin{tikzpicture}
  \coordinate (O) at (0, 0);

  \path[name path = para] (-1, -2.5) parabola bend (2, 2) (4, 0);

  \draw (O) -- (5, 0) coordinate (P1);

  \path[name path = circ] (O) circle[radius = .75bp];
  \path[name intersections = {of = para and circ}];

  \coordinate (A) at (intersection-1);
  \coordinate (B) at (intersection-2);

  \draw[-latex, red] (A) -- ($(B)!1cm!(A)$) coordinate (P2);

  \path (P1) -- (O) -- (P2)
  pic[''$\theta$'', draw, -latex, red, angle radius = .5cm,
  angle eccentricity = 1.2] {angle = P1--O--P2};
\end{tikzpicture}
\end{document}

It is telling me theta isn't a color.

Even if I load the quotes library and put double quotes around \theta as Harish Kumar has answered, I still receive the message:

! Missing \endcsname inserted.
<to be read again>
                   \theta
l.41   angle eccentricity = 1.2, font = \tiny]
                                               {angle = P1--O--P2};
! Missing \endcsname inserted.

 ...

l.41 ...y = 1.2, font = \tiny] {angle = P1--O--P2}
                                                  ;

! Package xcolor Error: Undefined color ```$\theta $'''.

For those who don't believe me that double quotes are causing the same problem, I narrated a video for you showing that this is the case.

https://www.dropbox.com/s/44zhedz2psg1vrk/2014-05-08%2018.08.46.mp4

Best Answer

You need to load quotes library to use quotes syntax. This enables the quotes syntax for labels, pins, edge nodes, and pic texts.

Also, it is double quotes like "$\theta$" (not ''$\theta$''). Some editors (such as Emacs) automatically convert " to `` or '' (depending on whether they are inserted at the start or end of a word) since that produces the right output after compiling the document. In this case, however, we want actual double quotes. To type these in Emacs, simply hit the double quote key twice in succession. The second one will convert the previously inserted two single quotes into a single double quote which is what is needed here.

\documentclass[tikz,varwidth]{standalone}%

\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\usetikzlibrary{angles}
\usetikzlibrary{quotes}

\begin{document}
\begin{tikzpicture}
  \coordinate (O) at (0, 0);

  \path[name path = para] (-1, -2.5) parabola bend (2, 2) (4, 0);

  \draw (O) -- (5, 0) coordinate (P1);

  \path[name path = circ] (O) circle[radius = .75bp];
  \path[name intersections = {of = para and circ}];

  \coordinate (A) at (intersection-1);
  \coordinate (B) at (intersection-2);

  \draw[-latex, red] (A) -- ($(B)!1cm!(A)$) coordinate (P2);

  \path (P1) -- (O) -- (P2) pic["$\theta$", draw,-latex, red, angle radius = 0.5cm, angle eccentricity = 1.2] {angle = P1--O--P2};
\end{tikzpicture}
\end{document}

enter image description here

Related Solutions

[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

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

As is explained in How do I draw shapes inside a tikz node? pics can be used for defining new objects. My main problem using pics is how to place where you want because they aren't nodes and positioning them is not so easy.

Following code shows how to define EDFA block.

    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}

In this case, coordinate (-1,0) will act as west anchor and 1,0 as east. Both point will have an special name for further reference. Every pic is placed according its own origin (0,0). You can use Claudio's answer to Anchoring TiKZ pics for better positioning.

As your example was simple, I'd prefer to star with EDFA and place Source and Sink after it.

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning

\begin{document}

\tikzset{%
    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}
    }
}

\begin{tikzpicture}[
block/.style={draw},
]

\draw pic (edfa) {EDFA};

\node[block, left=of edfain] (source) {Source};

\node[block, right= of edfaout] (sink) {Sink};

\draw[->] (source) -- (edfain);
\draw[->] (edfaout) -- (sink);

\end{tikzpicture}

\end{document}

I understand that your components are more complex than EDFA because for this particular case an isosceles triangle node with a label will do the work and it can be used as a node and not as a pic:

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning
\usetikzlibrary{shapes.geometric}

\begin{document}

\begin{tikzpicture}[
    block/.style={draw},
    edfa/.style={isosceles triangle, minimum width=1cm, 
         draw, anchor=west, isosceles triangle stretches, 
         minimum height=1cm, label=-80:#1}
]

\node[block] (source) {Source};

\node[edfa=1, right=of source] (edfa) {};

\node[block, right= of edfa] (sink) {Sink};

\draw[->] (source) -- (edfa);
\draw[->] (edfa) -- (sink);

\end{tikzpicture}

\end{document}

Best Answer

Related Solutions

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

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

Related Question