How to mark a Segment with an arrow in Tkz euclid with the \tkzMarkSegment

Question

I want to draw a light beam on a prism. I've looked and I found that their are a couple of options, but none with an arrow. Any suggestions for doing this in tkz-euclide environment?

\documentclass[a4paper]{article} 
\usepackage{tkz-euclide}
\usetikzlibrary{arrows, calc,intersections, decorations.pathmorphing}
%\usetkzobj{all} no need with tkz-euclide v >3
\usepackage{pgfplots}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=0.7]
\tkzInit[ymin=0,ymax=7.5,xmin=0,xmax=14]
\tkzClip
%\tkzGrid
\tkzDefPoints{2/1/A, 12/1/B, 7/7/C, 1/4.5/D, 12/6.5/E}
\tkzDrawPolygon(A,B,C)
\tkzDrawPoints[size=2pt](A,B,C)
\tkzInterLL(D,E)(A,C)  \tkzGetPoint{S}
\tkzDrawSegments(D,S)
\tkzMarkSegments[mark=||](D,S)
\end{tikzpicture}
\end{center}    
\end{document}

enter image description here

Do you mean that you just want an arrow pointing in the direction of the light beam into the prism? So just an arrow head on what's already there? — Christopher, Mar 23 '15 at 19:11
No I want an arrow in the middle of the line, on the place of the ||| — Arne Timperman, Mar 23 '15 at 19:17
Right, then see this answer which suggests that you can't do it just by writing [mark=>>] (which would be nice) but you have to create a custom style. — Thruston, Mar 23 '15 at 19:18
Thanks for this link, so it is not possible to adapt the option of the mark with the \tkzMarkSegment? — Arne Timperman, Mar 23 '15 at 19:23
You could create a dummy point in the middle and draw the line there which would work as a hack but the answer linked by @Thruston is the more elegant. — Christopher, Mar 23 '15 at 19:25

score 5 · Answer 1 · edited Feb 05 '20 at 07:12

Maybe it's not quite you want (you didn't tell us where the arrow must be placed), but if you replace

\tkzDrawSegments(D,S)

by

\tkzDrawSegments[arrows=->](D,S)

you get an arrow at the end of the segment:

enter image description here

Edit As said in the comments, here is a way to put the arrow in the middle of the segment. (Using the decorations.markings marking library.)

\documentclass[a4paper]{article} 
\usepackage{tkz-euclide} %euclide loads base
\usetikzlibrary{arrows, calc,intersections, decorations.pathmorphing, decorations.markings}
%\usetkzobj{all} % inutile avec une version >= 3.01
\usepackage{pgfplots}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=0.7]
\tkzInit[ymin=0,ymax=7.5,xmin=0,xmax=14]
\tkzClip
%\tkzGrid
\tkzDefPoints{2/1/A, 12/1/B, 7/7/C, 1/4.5/D, 12/6.5/E}
\tkzDrawPolygon(A,B,C)
\tkzDrawPoints[size=2pt](A,B,C);
\tkzInterLL(D,E)(A,C)  \tkzGetPoint{S}
\begin{scope}[decoration={
    markings,
    mark=at position 0.5 with {\arrow{>}}}
    ] 
    \tkzDrawSegments[postaction={decorate}](D,S)
\end{scope}
\end{tikzpicture}
\end{center}    
\end{document}

Output:

enter image description here

Then the answer is here: http://tex.stackexchange.com/questions/3161/tikz-how-to-draw-an-arrow-in-the-middle-of-the-line. I will soon edit my answer accordingly. — Franck Pastor, Mar 23 '15 at 19:32
Thanks for your efforts, I thought it was possible without a lot of code. But my problem is solved now. — Arne Timperman, Mar 23 '15 at 19:44

score 1 · Accepted Answer · edited Feb 05 '20 at 05:16

I've combined the advice of the others and put all together. (I'm not sure if this is the good way of doing this in this forum?)

\documentclass[a4paper]{article} 
\usepackage{tkz-euclide}
\usetikzlibrary{arrows, calc,intersections, decorations.pathmorphing}
\usetkzobj{all} 
\usepackage{pgfplots}

\tikzset{
arrowMe/.style={postaction=decorate,
    decoration={markings, mark=at position .5 with {\arrow[thick]{#1}}
    } }}

\begin{document}
\begin{center}
\begin{tikzpicture}[scale=0.7]
\tkzInit[ymin=0,ymax=7.5,xmin=0,xmax=14]
\tkzClip
%\tkzGrid
\tkzDefPoints{2/1/A, 12/1/B, 7/7/C, 1/4.5/D, 12/6.5/E}
\tkzDrawPolygon[fill=red!30](A,B,C)
\tkzInterLL(D,E)(A,C)  \tkzGetPoint{S}
\tkzDrawSegments(D,S)
\tkzDrawSegments[arrowMe=stealth](D,S)
\end{tikzpicture}
\end{center}    
\end{document}

enter image description here

How to mark a Segment with an arrow in Tkz euclid with the \tkzMarkSegment

2 Answers2

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