# How can I mark right angles in tkz-euclide with round quarter-circle and a dot?

I am currently re-creating this Wikipedia image:

The image I currently have is good, but I miss the round right-angle markers with dots:

Is there a possibility to re-define the \tkzMarkRightAngle to use the other notation (which is commonly used in school in Germany).

## MWE

\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{tkz-euclide}

\begin{document}
\usetkzobj{all}
\begin{tikzpicture}
\tkzSetUpPoint[shape=circle,size=10,color=black,fill=black]
\tkzSetUpLine[line width=1]
\tkzDefPoints{0/0/O, -5/0/A, 5/0/B, 5/5/M, -5/5/N}
\tkzDefPoint(60:5){X}
\tkzDefPoint(150:5){Y}

\tkzDrawArc[color=black, thick, fill=gray!20](O,B)(A)

% Avoid too long edges of polygon
\tkzClipPolygon(A,B,M,N)
\tkzClipCircle(O,B)

% Draw polygons and mark right angle
\tkzDrawPolygon[fill=red,fill opacity=0.5](A,B,X)
\tkzMarkRightAngle(A,X,B)

\tkzDrawPolygon[fill=blue,fill opacity=0.5](A,B,Y)
\tkzMarkRightAngle(A,Y,B)

% lines should not colored
\tkzDrawPolygon(A,B,X)
\tkzDrawPolygon(A,B,Y)

\tkzDrawArc[color=black, thick](O,B)(A)
\end{tikzpicture}
\end{document}

• I think right angle must be a right angle without the arc. In the first one it only says that the angles are equal. – percusse Oct 20 '14 at 20:24
• @percusse In schools in Germany an angle with a dot denote always a right angle. Probably not the best notation, but very common. – Martin Thoma Oct 20 '14 at 20:34

You should use the pic[draw,...]{angle=p1--p2--p3} construct instead of \tkzMarkRightAngle(p1,p2,p3) then. This can be done easily as the following:

\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{tkz-euclide}
\usetikzlibrary{angles,quotes}

\begin{document}
\usetkzobj{all}
\begin{tikzpicture}[line width=1]\Large
\tkzSetUpPoint[shape=circle,size=10,color=black,fill=black]
\tkzSetUpLine[line width=1]
\tkzDefPoints{0/0/O, -5/0/A, 5/0/B, 5/5/M, -5/5/N}
\tkzDefPoint(60:5){X}
\tkzDefPoint(150:5){Y}

\tkzDrawArc[color=black, thick, fill=gray!20](O,B)(A)

% Avoid too long edges of polygon
\tkzClipPolygon(A,B,M,N)
\tkzClipCircle(O,B)

% Draw polygons and mark right angle
\tkzDrawPolygon[fill=red,fill opacity=0.5](A,B,X)
\draw pic[draw, angle radius=3mm,"$\cdot$",angle eccentricity=.6]{angle= A--X--B};

\tkzDrawPolygon[fill=blue,fill opacity=0.5](A,B,Y)
\draw pic[draw, angle radius=3mm,"$\cdot$",angle eccentricity=.6]{angle= A--Y--B};

% lines should not colored
\tkzDrawPolygon(A,B,X)
\tkzDrawPolygon(A,B,Y)

\tkzDrawArc[color=black, thick](O,B)(A)
\end{tikzpicture}
\end{document}


with the required output:

Here is the tkz-euclide way of doing it.

\tkzMarkAngle[thick,size=0.4](A,X,B)
\tkzLabelAngle[pos=0.25](A,X,B){$\cdot$}


and

\tkzMarkAngle[thick,size=0.4](A,Y,B)
\tkzLabelAngle[pos=0.25](A,Y,B){$\cdot$}


Full code:

\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{tkz-euclide}

\begin{document}
\usetkzobj{all}
\begin{tikzpicture}
\tkzSetUpPoint[shape=circle,size=10,color=black,fill=black]
\tkzSetUpLine[line width=1]
\tkzDefPoints{0/0/O, -5/0/A, 5/0/B, 5/5/M, -5/5/N}
\tkzDefPoint(60:5){X}
\tkzDefPoint(150:5){Y}

\tkzDrawArc[color=black, thick, fill=gray!20](O,B)(A)

% Avoid too long edges of polygon
\tkzClipPolygon(A,B,M,N)
\tkzClipCircle(O,B)

% Draw polygons and mark right angle
\tkzDrawPolygon[fill=red,fill opacity=0.5](A,B,X)
\tkzMarkAngle[thick,size=0.4](A,X,B)
\tkzLabelAngle[pos=0.25](A,X,B){$\cdot$}

\tkzDrawPolygon[fill=blue,fill opacity=0.5](A,B,Y)
\tkzMarkAngle[thick,size=0.4](A,Y,B)
\tkzLabelAngle[pos=0.25](A,Y,B){$\cdot$}

% lines should not colored
\tkzDrawPolygon(A,B,X)
\tkzDrawPolygon(A,B,Y)

\tkzDrawArc[color=black, thick](O,B)(A)
\end{tikzpicture}
\end{document}