Make curly braces wrap around part of a circle

Question

Essentially the same question as Draw Curly Braces in TikZ except that I want the brace to wrap around a circle to display an angular sector (for example 0-30 degrees). How can I do this?

---

I dont know if it is even possible, but here is a MWE

\documentclass[12pt]{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[scale=0.4]
\draw[style=thick] (0,0) circle (7);
\draw[thin,dashed] (0, 0 ) -- (100:7) ;
\draw[thin,dashed] (0, 0 ) -- (170:7) ;
\end{tikzpicture}
\end{document}

Answer 1

Here's a first version, the meeting point in the middle lokks still bad, but I'm working on it.

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}
\usepackage{ifthen}

\newcommand{\cucubr}[7]{%
%origin point, circle radius, start angle, end angle, distance c-b, brace radius, brace options
\pgfmathsetmacro{\helpangleedge}{atan(#6/(#2+#5+#6))}%
\pgfmathsetmacro{\helpanglemid}{atan(#6/(#2+#5+2*#6))}%
\pgfmathsetmacro{\halfangle}{(#4-#3)/2+#3}%
\pgfmathsetmacro{\innerradius}{#2+#5}%
\pgfmathsetmacro{\midradius}{#2+#5+#6}%
\pgfmathsetmacro{\outerradius}{#2+#5+2*#6}%
\pgfmathsetmacro{\firstmidanglestart}{mod(\halfangle-\helpanglemid+180,360)}%
\pgfmathsetmacro{\secondmidanglestart}{mod(\halfangle+\helpanglemid+180,360)}%
\pgfmathsetmacro{\firstmidanglestop}{mod(\halfangle-\helpanglemid+180,360)-90}%
\pgfmathsetmacro{\secondmidanglestop}{mod(\halfangle+\helpanglemid+180,360)+90}%
%
\draw[#7] (#1) ++ (#3:\innerradius) arc (#3+270:#3+360:#6) arc (#3+\helpangleedge:\halfangle-\helpanglemid:\midradius) arc (\firstmidanglestart:\firstmidanglestop:#6);%
\draw[#7] (#1) ++ (#4:\innerradius) arc (#4+90:#4:#6) arc (#4-\helpangleedge:\halfangle+\helpanglemid:\midradius) arc (\secondmidanglestart:\secondmidanglestop:#6);% node[black, text width=2.5cm,draw] {mid:\firstmidanglestart, one:\firstmidanglestop, two:\secondmidanglestop, half:\halfangle};%
}

\begin{document}

\begin{tikzpicture}
\draw (0,0) -- (0:4) arc (0:90:4) -- cycle;
\draw (0,0) -- (90:4) arc (90:180:4) -- cycle;
\draw (0,0) -- (180:4) arc (180:270:4) -- cycle;
\draw (0,0) -- (270:4) arc (270:360:4) -- cycle;
\cucubr{0,0}{4}{0}{90}{0.4}{0.5}{thick,red}
\cucubr{0,0}{4}{90}{180}{0.9}{1.0}{thick,green}
\cucubr{0,0}{4}{180}{270}{0.2}{0.3}{thick,blue}
\cucubr{0,0}{4}{270}{360}{0.6}{0.6}{thick,teal}
\end{tikzpicture}

\end{document}

---

Edit 1: I got a much better variant than before, it involves more math now. While this should be correct, I still got variations, so the brace would't always close in the middle. I think my math is correct, and I ran into some computation deviations in TikZ: the angles computed by TikZ vary by up to 0.35 degrees from the real. While this does does not seem much, it was up to 10% of the angle, or the equivalent of 1.5 linewidths. As I found no way around, I decided to start drawing from the center. That way the brace ends meet in the middle, and I only needed to adapt one value due to deviations. Here's the final code:

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}

\newcommand{\cucubr}[7]{%
%origin point, circle radius, start angle, end angle, distance c-b, brace radius, brace options
\pgfmathsetmacro{\helpangleedge}{acos(1-pow(#6,2)/2/pow(#2+#5,2))}%
\pgfmathsetmacro{\turnangleedge}{90+(\helpangleedge/2)}%
\pgfmathsetmacro{\helpanglemid}{acos(1-pow(#6,2)/2/pow(#2+#5+2*#6,2))}%
\pgfmathsetmacro{\turnanglemid}{90-(\helpanglemid/2)}%
\pgfmathsetmacro{\halfangle}{(#4-#3)/2+#3}%
\pgfmathsetmacro{\midradius}{#2+#5+#6}%
\pgfmathsetmacro{\outerradius}{#2+#5+1.88*#6}%
\pgfmathsetmacro{\firstmidanglestart}{mod(\halfangle-\helpanglemid+180,360)}%
\pgfmathsetmacro{\secondmidanglestart}{mod(\halfangle+\helpanglemid+180,360)}%
\pgfmathsetmacro{\firstmidanglestop}{mod(\halfangle-\helpanglemid/2+180,360)-\turnanglemid}%
\pgfmathsetmacro{\secondmidanglestop}{mod(\halfangle+\helpanglemid/2+180,360)++\turnanglemid}%
%
\draw[#7] (#1) ++ (\halfangle:\outerradius) arc (\firstmidanglestop:\firstmidanglestart:#6) arc (\halfangle-\helpanglemid:#3+\helpangleedge:\midradius) arc (#3+270+\turnangleedge+\helpangleedge/2:#3+270+\helpangleedge/2:#6) ;%
%
\draw[#7] (#1) ++ (\halfangle:\outerradius) arc (\secondmidanglestop:\secondmidanglestart:#6) arc (\halfangle+\helpanglemid:#4-\helpangleedge:\midradius) arc (#4+90-\turnangleedge-\helpangleedge/2:#4+90-\helpangleedge/2:#6);%
}

\begin{document}

\begin{tikzpicture}
\draw (0,0) -- (00:4) arc (0:90:4) -- cycle;
\draw (0,0) -- (90:4) arc (90:180:4) -- cycle;
\draw (0,0) -- (180:4) arc (180:270:4) -- cycle;
\draw (0,0) -- (270:4) arc (270:360:4) -- cycle;
\cucubr{0,0}{4}{0}{90}{0.4}{0.5}{red,densely dotted}
\cucubr{0,0}{4}{90}{180}{0.9}{1.0}{thin,green}
\cucubr{0,0}{4}{180}{270}{0.2}{0.3}{ultra thick,blue,densely dashed}
\cucubr{0,0}{4}{270}{360}{0.6}{0.6}{thick,teal,-latex}
\end{tikzpicture}

\end{document}

---

Edit 2: I double and tripple checked the math, it really, really should be correct. So I started investigating the deviations when calculating. The TikZ manual states that the power and accuracy of it's engine are limited due to limitations of TeX. Sadly, this is the first time I ran into them. I calculated the values of the angles I needed for different values of circle radius and brace radius:

The values should decrease left to right and top down, but for small radii they don't. As this limits the accuracy achievable, I decided to choose yet another approach: starting the brace from inside and outside, and then connecting the pieces via to[out=<degrees>,in=<degrees>]. This looks well enough, at least if you don't choose a lage brace radius for a small circle radius.

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}
\usetikzlibrary{calc}

\pgfkeys{/tikz/savenumber/.code 2 args={\global\edef#1{#2}}}

\newcommand{\cucubr}[7]{%
%origin point, circle radius, start angle, end angle, distance c-b, brace radius, brace options
\pgfmathsetmacro{\helpangleedge}{acos(1-pow(#6,2)/2/pow(#2+#5,2))}%
\pgfmathsetmacro{\turnangleedge}{90+(\helpangleedge/2)}%
\pgfmathsetmacro{\helpanglemid}{acos(1-pow(#6,2)/2/pow(#2+#5+2*#6,2))}%
\pgfmathsetmacro{\turnanglemid}{90-(\helpanglemid/2)}%
\pgfmathsetmacro{\halfangle}{(#4-#3)/2+#3}%
\pgfmathsetmacro{\innerradius}{#2+#5}%
\pgfmathsetmacro{\midradius}{#2+#5+#6}%
\pgfmathsetmacro{\outerradius}{#2+#5+2*#6-sqrt(1/#2)*0.01}%
\pgfmathsetmacro{\firstmidanglestart}{mod(\halfangle-\helpanglemid+180,360)}%
\pgfmathsetmacro{\secondmidanglestart}{mod(\halfangle+\helpanglemid+180,360)}%
\pgfmathsetmacro{\firstmidanglestop}{mod(\halfangle-\helpanglemid/2+180,360)-\turnanglemid}%
\pgfmathsetmacro{\secondmidanglestop}{mod(\halfangle+\helpanglemid/2+180,360)+\turnanglemid}%
%
\draw[#7] (#1) ++ (\halfangle:\outerradius) arc (\firstmidanglestop:\firstmidanglestart:#6) node (A) {};%
\draw[#7] (#1) ++ (#3:\innerradius) arc (#3+270+\helpangleedge/2:#3+270+\turnangleedge+\helpangleedge/2:#6) node (B) {};%
%
\draw[#7] (#1) ++ (\halfangle:\outerradius) arc (\secondmidanglestop:\secondmidanglestart:#6) node (C) {};%
\draw[#7] (#1) ++ (#4:\innerradius) arc (#4+90-\helpangleedge/2:#4+90-\turnangleedge-\helpangleedge/2:#6) node (D) {};%
%
\draw[#7] (A.center) to[out=\firstmidanglestop+180,in=#3+90+\helpangleedge/2] (B.center);%
\draw[#7] (C.center) to[out=\secondmidanglestop-180,in=#4-90-\helpangleedge/2](D.center);%
}

\begin{document}

\begin{tikzpicture}
\draw[very thin,gray,densely dotted] (0,0) -- (20:7);
\draw[very thin,gray,densely dotted] (0,0) -- (80:7);
\draw[very thin,gray,densely dotted] (0,0) -- (150:7);
\foreach \r in {1,...,6}
{   \cucubr{0,0}{\r}{20}{80}{0.2}{0.3}{blue}
    \cucubr{0,0}{\r}{80}{150}{0.5}{0.5}{red}
}
\end{tikzpicture}

\end{document}

As you can see, the smaller braces look "staircasey", but this vanishes with higher ratios of circle radius to brace radius.

Answer 2

Finally I get the next code without "big" calculus.

Update version 2

I added some keys like tip angle and find something better for the tip.

Figure

Details

Code

\documentclass[11pt]{scrartcl}
\usepackage{tikz}

\makeatletter 

\tikzset{curlybrace/.style={rounded corners=2pt,line cap=round}}%  
\pgfkeys{%
/curlybrace/.cd,%
tip angle/.code     =  \def\cb@angle{#1},
/curlybrace/.unknown/.code ={\let\searchname=\pgfkeyscurrentname
                              \pgfkeysalso{\searchname/.try=#1,
                              /tikz/\searchname/.retry=#1}}}  
\def\curlybrace{\pgfutil@ifnextchar[{\curly@brace}{\curly@brace[]}}%

\def\curly@brace[#1]#2#3#4{% 
\pgfkeys{/curlybrace/.cd,
tip angle = 0.75}% 
\pgfqkeys{/curlybrace}{#1}% 
\ifnum 1>#4 \def\cbrd{0.05} \else \def\cbrd{0.075} \fi
\draw[/curlybrace/.cd,curlybrace,#1]  (#2:#4-\cbrd) -- (#2:#4) arc (#2:{(#2+#3)/2-\cb@angle}:#4) --({(#2+#3)/2}:#4+\cbrd) coordinate (curlybracetipn);
\draw[/curlybrace/.cd,curlybrace,#1] ({(#2+#3)/2}:#4+\cbrd) -- ({(#2+#3)/2+\cb@angle}:#4) arc ({(#2+#3)/2+\cb@angle} :#3:#4) --(#3:#4-\cbrd);
}

\begin{document}
\begin{tikzpicture}[scale=1.5]
\draw[help lines](-3,-3) grid (3,3);
\curlybrace[color=blue,thick]{30}{60}{1.2}
\curlybrace[color=blue]{30}{60}{0.6}
\curlybrace[color=blue]{30}{60}{2}    
\draw circle(1cm);

\curlybrace[color=red]{90}{160}{3} \node[red,anchor=south] at (curlybracetipn) {$70^\circ$};
\curlybrace[color=red,thin]{90}{160}{1.2}
\curlybrace[color=red,thin]{90}{160}{0.6}
\curlybrace[color=red,thin]{90}{160}{0.3} 
\curlybrace[color=red,thin]{90}{160}{2} 
\curlybrace[color=red]{90}{160}{3} 
\curlybrace[color=green!40!black,thick]{180}{360}{1.2}
\curlybrace[color=green!40!black,thick]{180}{360}{0.6}
\curlybrace[color=green!40!black,thick]{180}{360}{0.3} 
\curlybrace[color=green!40!black,ultra thick,tip angle=2]{180}{360}{3}   
\end{tikzpicture}
\end{document} 

Todo

It's possible to add :

1. a coordinate to place a label at the middle of the brace (do)
2. some keys with pgfkeys to get a better control for rounded corners, for the little angle that I use at the middle of the brace (0.75 degree). We can calc this angle function of the radius.(do)
3. expression to calc some values according to the radius like \def\cbrd{0.05}we can avoid this with some calculus.
4. styles with pgfkeys to add arrows for example. it's easy (do)
5. to get a better junction at the middle, it would be interesting to use only one path . Actually the result is fine with line width not to big.(do with line cap=round)

First idea

It was to begin with a simple code to get some coordinates and then to add some ornaments but finally "rounded corners" was enough.

\documentclass[11pt]{scrartcl}
\usepackage{tikz}

\newcommand{\curlybrace}[3]{%
\draw  (#1:#3-0.1) -- (#1:#3) arc (#1:#2:#3)--(#2:#3-0.1) ; 
\draw ({(#1+#2)/2}:#3) -- ({(#1+#2)/2}:#3+0.1);}
\begin{document}
\begin{tikzpicture}[scale=1]
\draw[help lines](-3,-3) grid (3,3);
\curlybrace{30}{60}{1.2}
\curlybrace{30}{60}{2}    
\draw circle(1cm);

\curlybrace{90}{160}{1.2}
\curlybrace{90}{160}{2}  
\end{tikzpicture} 
\end{document} 

Answer 3

This is the PMB (poor man's brace) version.

It uses the arrow styles right to reserved and left to reserved from the arrow library.

The solution isn't very sophisticated as it enables one only to draw braces around (0,0). (The shift key is already used, so an outer scope is necessary here.)

Next step would be to include this in some kind of style of to or arc which I won't follow up because we already have Alain Matthes's solution.

Code

\documentclass[
    tikz,
    border=2pt,
]{standalone}
\usetikzlibrary{arrows}
\newcommand*{\braceme}[6][]{% #1 = optional
                            % #2 = radius
                            % #3 = start angle
                            % #4 = end angle
                            % #5 = node name
                            % #6 = node content
\draw[
    shift={(#3:#2)},
    right to reversed-right to reversed,
    shorten >=-.75\pgflinewidth,
    #1
    ] (0,0)
        arc[radius=#2, start angle=#3, end angle=#3+(#4-#3)/2] node[rotate=#3+(#4-#3)/2-90,above=2pt] (#5) {#6};
\draw[
    shift={({#3+(#4-#3)/2}:#2)},
    left to reversed-left to reversed,
    shorten <=-.75\pgflinewidth,
    #1
    ] (0,0)
        arc[radius=#2, start angle=#3+(#4-#3)/2, end angle=#4];
}
\begin{document}
\begin{tikzpicture}[scale=0.4]
\draw[style=thick] (0,0) circle (7);
\draw[thin,dashed] (0, 0 ) -- (100:7) ;
\draw[thin,dashed] (0, 0 ) -- (170:7) ;
\braceme[thick]{7.5}{100}{170}{br1}{Hi!}
\braceme[thick]{8}{180}{390}{br2}{Test?}
\end{tikzpicture}
\end{document}

Output

Answer 4

Is this what you had in mind?

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing} 

\begin{document}
\begin{tikzpicture}
  \draw (0,0) circle (1);
  \draw (0,0) -- (1,0);
  \draw (0,0) -- (30:1);
  \draw [decorate,decoration={brace,amplitude=2pt,mirror,raise=4pt}] (1,0) -- (30:1);
\end{tikzpicture}
\end{document}