How to Mark Right Angle in Tikz

Question

I consider this question unanswered as I would like a minimal example. The examples I've seen are for very complex shapes and I get lost in the immensity and complexity of the code. This question is different from the red square solution as I'd like to be able to have a certain compat in pfgplots. Also, I'd like to be able to put in exact values for a coordinate point (sqrt(75) for example). I get an error when I do that, but putting something in like 8.66 works just fine. This is not a duplicate, no more reporting it as one, please.

\documentclass[11pt]{exam}

\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}

\begin{document}

\begin{tikzpicture}
\draw (-5,0) -- (5,0);
\draw (0,0) -- (0,5);
\end{tikzpicture}

\end{document}

What would be the simplest way to mark 90 degrees on this diagram.

I was hoping for more of a specific function for right angle marks instead of having one of size 0.5 all of the time. Because, what if the lines themselves are only about 0.5 long? I was hoping there's some sort of function in Tikz or pgf that scales the angle mark. — ZackaryCW, Mar 04 '17 at 06:46
I don't think there is any such macro present in TikZ, so one would have to create it. The tkz-euclide package defines a macro for marking the right angle between three named coordinates (see e.g. http://tex.stackexchange.com/a/154354/586), but that has a fixed default size, so you would have to change it manually for cases when it is not suitable. — Torbjørn T., Mar 04 '17 at 08:12
Regarding your edit, neither the compat setting for pgfplots nor the coordinate specification has any relevance for the question at hand I think. The coordinate specification is a different question altogether, and I think the compat setting would only be relevant if you're trying to mark angles inside an axis environment. — Torbjørn T., Mar 04 '17 at 09:18

CarLaTeX · Accepted Answer · 2017-03-04T08:24:00.607

13

You can use also tkz-euclide:

\documentclass[11pt]{exam} 
\usepackage{tkz-euclide}
\usetkzobj{all}

\begin{document} 
    \begin{tikzpicture} 
        \coordinate (A) at (-5, 0) {};
        \coordinate (B) at (5, 0) {};
        \coordinate (C) at (0, 5) {};
        \coordinate (0) at (0, 0) {};

        % left angle
        \tkzMarkRightAngle[draw=blue,size=.7](A,0,C);
        \tkzLabelAngle[dist=.5](A,0,C){$\alpha$};

        % right angle
        \tkzMarkRightAngle[draw=red,size=.7](B,0,C);
        \tkzLabelAngle[dist=.5](B,0,C){$\beta$};

        % axis lines
        \tkzDrawLines[add=0 and 0, arrows=->](A,B 0,C)

    \end{tikzpicture}
\end{document}

edited Mar 04 '17 at 08:24

answered Mar 04 '17 at 08:15

CarLaTeX

62,716

I included all of that in the pre-amble, copy and pasted code in a blank new document... and I get errors. "undefined control sequence. \coordiante" – ZackaryCW Mar 04 '17 at 08:33
that was a typo, yes I copied it right. I set pgf compat to a different version, is that why? Besides that, everything else is the same – ZackaryCW Mar 04 '17 at 08:37
My preamble - \usepackage{amsmath} \usepackage{tikz} \usepackage{pgfplots} \pgfplotsset{compat=1.9} \usepackage{gensymb} \usepackage{tkz-euclide} \usetkzobj{all} – ZackaryCW Mar 04 '17 at 08:46
@ZackaryCW The compat setting only applies to the pgfplots package, and that's not being used at all in any code here. \coordinate is defined by TikZ, and works only inside a tikzpicture environment. CarLaTeX's code works as it is presented. – Torbjørn T. Mar 04 '17 at 08:49
1

@ZackaryCW Even with your preamble my code works, I think the error is elsewhere, it is better if you post another question with a mwe that reproduces the error... – CarLaTeX Mar 04 '17 at 08:50
This diagram I'm trying to draw only has Tikz elements. However, there is another section in the exam that I needed pgfplots for, that's why it's there. – ZackaryCW Mar 04 '17 at 08:51
@ZackaryCW It you want to ping a user who is not the poster, you have to use @ followed by the nickname (in this case @Torbjorn). However, as I already said, my code works even if pgfplots is loaded, that is not the error... – CarLaTeX Mar 04 '17 at 08:54

score 3 · Answer 2 · answered Mar 04 '17 at 08:48

You can use perpendicular syntax. It saves typing the coordinate at corner.

\documentclass[tikz,border=2mm]{standalone} 
\usetikzlibrary{positioning}

\begin{document}
\begin{tikzpicture}
\draw (-5,0) -- (5,0);
\draw (0,0) -- (0,5);

\draw (-.3,0)|-(0,.3) (0,.5)-|(.5,0);
\end{tikzpicture}
\end{document}

How to Mark Right Angle in Tikz

2 Answers2

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