[Tex/LaTex] How to mark a Segment with an arrow in Tkz euclid with the \tkzMarkSegment

tkz-euclide

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

Best Answer

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)

\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

Related Solutions

[Tex/LaTex] Mark angles with arrows using tkz-euclide

Here's an example (stolen shamelessly from the tkz-euclide manual):

\documentclass{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetikzlibrary{calc}
\usetkzobj{all}
\pagestyle{empty}
\begin{document}

\begin{tikzpicture}[scale=2]
  \tkzDefPoint(0,0){O}
  \tkzDefPoint(2,-1){A}
  \tkzDefPoint(2,2){B}
  \tkzDefPointsBy[symmetry=center O](B,A){}
  \tkzDrawLine(A,A')
  \tkzDrawLine(B,B')
  \tkzMarkAngle[mark=s,arc=l,size=2 cm,mkcolor=red,line width=2pt,arrows=->](A,O,B)
\end{tikzpicture}

\end{document}

enter image description here

But you can also use decorations as here:

\documentclass{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetikzlibrary{calc}
\usetkzobj{all}
\pagestyle{empty}
\begin{document}

\begin{tikzpicture}[scale=2,my arrow/.style={decorate,decoration={markings,mark=at position 1 with {\arrow[scale=4]{>}};}}]
  \tkzDefPoint(0,0){O}
  \tkzDefPoint(2,-1){A}
  \tkzDefPoint(2,2){B}
  \tkzDefPointsBy[symmetry=center O](B,A){}
  \tkzDrawLine(A,A')
  \tkzDrawLine(B,B')
  \tkzDrawArc[postaction={my arrow}](O,A)(B)
\end{tikzpicture}

\end{document}

To get

enter image description here

UPDATE

It seems that mark=at position 1 with ... doesn't always work when TikZ thinks that 1 is past the end of the path. So, you can modify this by using

mark=at position -0.1pt with ...

The negative distance tells TikZ to place the decoration at the end of the path. I'd recommend a negligible distance. Also, if you've loaded the TikZ library calc, you can write something like

\coordinate (tOA) at ($(O)!2cm!(A)$);
\tkzDrawArc[postaction={my arrow}](O,tOA)(B)

to control how far from the angle vertex the arc is placed.

[Tex/LaTex] How to label a segment in `tkz-euclide`

You can do it with \tkzLabelSegment.

I took the liberty to adjust also the bc label:

\documentclass[11pt,a4paper]{article}
\usepackage{tkz-euclide}
\usetkzobj{all}

\begin{document}
    \begin{tikzpicture}
    \tkzInit[xmin=-2,xmax=3,ymin=-2,ymax=3]
    \tkzAxeXY

    \tkzDefPoint[label=below:{$A$}](-1,-1){A}
    \tkzDefPoint[label=right:{$B$}](3,1){B}
    \tkzDefPoint[label=above:{$C$}](1,2){C}
    \tkzDrawSegments(A,B B,C C,A)
    \tkzDefPointBy[projection=onto A--C](B)

    \tkzDefPoint(2,1.5){BC}
    \tkzLabelSegment[above right=-2pt and -2pt](B,C){$bc$}  
    \tkzDrawSegments(A,BC)
    \tkzLabelSegment[above=1pt](A,BC){$M$}  

    \end{tikzpicture}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Mark angles with arrows using tkz-euclide

[Tex/LaTex] How to label a segment in `tkz-euclide`

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