# Circle helper lines for Spirograph aligning purposes

I use the following code, inspired by Dario Orescanin, to draw a circle with helper lines, for Spirograph aligning purposes.

\documentclass{beamer}
\usepackage{tikz}
\usepackage{verbatim}
\begin{document}
\begin{frame}[t]
\frametitle{circle helper lines}
\begin{center}
\vskip -.6cm
\begin{tikzpicture}[scale=2.]
\node[draw, circle, black, line width=.1mm, inner sep=.01mm] (a) at (0,0) {.};
\foreach \x in {0,11.25,...,359}
{
\node[scale=.6, red] at (360+\x:\labelrad*1.36) {$\x^\circ$};
\draw [red,line width=.1mm] (a) -- (\x:\radius);
};
\end{tikzpicture}
\end{center}
\end{frame}
\end{document}


For a 4-side figure, I need lines every 11.25 angle, using the code

\foreach \x in {0,11.25,...,359}

For a 3-side figure, I need lines every 10 angle

For a 7-side figure, I need lines every 12.857 angle

and so on.

To simplify the needed calculations, is there a way to modify the used code to be

\foreach \x in {360/8/4*0, 360/8/4*1, ...,359}

\foreach \x in {360/3/3/4*0, 360/3/3/4*1, ...,359}

\foreach \x in {360/7/4*0, 360/7/4*1, ...,359}

This is not a complete answer since I really do not understand your prescription. There is a simple formula that covers the cases n=3,...,7, but perhaps not beyond:

  Delta alpha (n) = 15 -15/n .


If you kindly explain the logic of these graphs a bit more I am confident to be able to generalize it further.

Here is what I have so far. One only needs to adjust the formula to go beyond.

\documentclass{beamer}
\usepackage{tikz}
\tikzset{pics/helper lines/.style={code={
\tikzset{helper lines/.cd,#1}
\def\pv##1{\pgfkeysvalueof{/tikz/helper lines/##1}}
\draw [green](0,0) node[ball color=gray,inner sep=1.5pt,circle,draw] (a){} circle[radius=\pv{r}];
\pgfmathsetmacro{\nextX}{15-15/\pv{n}}
\foreach \XX in {0,\nextX,...,359}
{\node[scale=.6, red,anchor=\XX+180] at (360+\XX:\pv{r}) {$\pgfmathprintnumber{\XX}^\circ$};
\draw [red,line width=.1mm] (a) -- (\XX:\pv{r});
}
\foreach \XX in {0,...,359}
{\draw[green,line width=.1mm] (\XX:\pv{dr}) -- (\XX:\pv{r});}
}},
helper lines/.cd,r/.initial=2cm,dr/.initial=1.88cm,n/.initial=3}
\usepackage{verbatim}
\begin{document}
\foreach \X in {3,4,...,7}
{\begin{frame}[t]
\frametitle{Circle helper lines: $n=\X$}
\begin{tikzpicture}
\pic[scale=1.8] {helper lines={n=\X}};
\end{tikzpicture}
\end{frame}}
\end{document}


• @ Schrödinger's cat I want helper lines to align rotated patterns correctly. When I use, for example, an 8-side pattern as in i.stack.imgur.com/1XiUd.png, I calculate the exact rotation angle by using the equation 360/8/4 which gives 11.25. When trying to rotate a 23-side pattern, to make the uppermost spike vertical, I have to make several attempts to get the right rotation angle. So I need helper lines with 360/23/4 angles to get the correct needed rotation angle instead of doing several calculations to get it. That is why I need to use this equation in the foreach loop. – Hany Feb 7 at 14:13
• @ Schrödinger's cat. That is why I need to use 360/23/4 equation inside the \foreach loop: \foreach \x in {360/23/4 *0, 360/23/4*1,360/23/4*2} and so on. – Hany Feb 7 at 14:22