# Tick Marks in Geometry

Here is an excerpt from my code:

\begin{tikzpicture}[scale=5.5]
\coordinate[label=left:$A$]  (A) at (0,0);
\coordinate[label=right:$B$]  (B) at (1,0);
\coordinate[label=:$C$]  (C) at (0.5,0.866);
\draw[] (A)--(B)--(C)--(A);
\end{tikzpicture}


I want to denote AB=BC using the tick mark notation. Also, point C isn't exactly where it should be. How can I fix that? I rounded sqrt(3)/2 to 0.866. One last thing: I only want single tick marks.

• Welcome to TeX.SE! Please show us -- as usual here --an short compilable code resulting in your issue ... Jan 7, 2019 at 22:53
• It would also be helpful if you could include a sketch of how the output should look like. Jan 7, 2019 at 22:59
• TikZ understands polar coordinates such as coordinate[label=:$C$] (C) at (60:1); It also understands coordinate[label=:$C$] (C) at (0.5,{sqrt(3)/2});.
– user121799
Jan 7, 2019 at 23:02

Welcome to TeX.SE! You can add these marks with decorations.markings. Since you want two of them, it is shorter to use the .list key for that. Further, TikZ understands polar coordinates, and it also understands (0.5,{sqrt(3)/2}), so there is no need to unbury your calculator. ;-)

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[scale=5.5,equal mark/.style={postaction={decorate,
decoration={markings,mark=at position #1 with {\draw (-2pt,-4pt) -- (-2pt,4pt);
\draw (2pt,-4pt) -- (2pt,4pt);}}}}]
\coordinate[label=left:$A$]  (A) at (0,0);
\coordinate[label=right:$B$]  (B) at (1,0);
\coordinate[label=:$C$]  (C) at (60:1);
\draw[equal mark/.list={1/6,1/2}] (A)--(B)--(C)--cycle;
\end{tikzpicture}
\end{document}


As you can see, this code starts with \documentclass and ends with \end{document}, and is compilable.

And you may simplify/shorten the code using a \foreach loop.

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[scale=5.5,equal mark/.style={postaction={decorate,
decoration={markings,mark=at position #1 with {\draw (-2pt,-4pt) -- (-2pt,4pt);
\draw (2pt,-4pt) -- (2pt,4pt);}}}}]
\foreach \X/\Y in {210/A,-30/B,90/C}
{\coordinate[label=\X:$\Y$]  (\Y) at (\X:{1/sqrt(3)});}
\draw[equal mark/.list={1/6,1/2,5/6}] (A)--(B)--(C)--cycle;
\end{tikzpicture}
\end{document}


A PSTricks solution just for fun purposes.

\documentclass[pstricks,12pt,border=1cm]{standalone}
\usepackage{pst-eucl}
\begin{document}
\pspicture[MarkAngle=90](-4,4)
\pstTriangle(4;150){C}(-4,0){A}(0,0){B}
\pstSegmentMark{A}{B}
\pstSegmentMark{B}{C}
\endpspicture
\end{document}


# Bonus

\documentclass[pstricks,12pt,border=1cm]{standalone}
\usepackage{pst-eucl}
\begin{document}
\foreach \i in {90,100,...,170}{%
\pspicture[MarkAngle=90](-4,4)
\pstTriangle(4;\i){C}(-4,0){A}(0,0){B}
\pstSegmentMark{A}{B}
\pstSegmentMark{B}{C}
\endpspicture}
\end{document}


one more tikz solution. for marks are used math symbol \| in nodes with option sloped placed on lines:

\documentclass[tikz,border=3.141592mm]{standalone}

\begin{document}
\begin{tikzpicture}[scale=5.5]
\coordinate[label=left:$A$]     (A) at (0,0);
\coordinate[label=right:$B$]    (B) at (1,0);
\coordinate[label=$C$]          (C) at (0.5,0.866);
\draw (A) -- node {$\|$} (B) -- node[sloped] {$\|$} (C) -- (A);
\end{tikzpicture}
\end{document}


now tikz version 3.1 in miktex works ...

• The mark on BC is not perpendicular I think ( I compile with my heart). Jan 8, 2019 at 1:17
• @GodMustBeCrazy, of course not, i forgot to add option sloped ... i correct this. Jan 8, 2019 at 1:21