Draw n lines in a loop around a circle

Question

I am trying to draw \nb lines from (0,0). All equally spaced.

I keep getting the error "Missing number treated as zero". I have found a lot of similar errors online; these are solved by enclosing the maths in {} curly brackets.

I have tried this but it still does not work. Does anybody know what my error is?

\begin{figure}[h]                                                                
    \centering                                                                   
    \begin{tikzpicture}                                                          
        \newcommand\ir{2}%Inner radius                                           
        \newcommand\nb{5}%Number of bars                                         
        \newcommand\tta{2*pi/\nb}
    \foreach \i in {1,...,\nb} {                                             
        \newcommand\ctta{{cos(deg(\i*\tta))}}                                
        \newcommand\stta{{sin(deg(\i*\tta))}}                                
        \newcommand\ttta{{tan(deg(\i*\tta))}}                                

        \newcommand\ltpcx{\ir*\ctta}                                         
        \newcommand\ltpcy{\ir*\stta}                                         
        \draw[] (0,0) -- (\ltpcx,\ltpcy);                                    
    }                                                                        
\end{tikzpicture}                                                            
\caption{General structure of a Data Bank in a MIDAS event.}                 
\label{fig:BV_structure}                                                     

\end{figure}

Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. — SebGlav, Sep 09 '21 at 17:13

Skillmon · Accepted Answer · 2021-09-09T18:07:02.843

5

Instead of calculating the points using sin and cos how about using the (<ang>:<rad>) syntax of TikZ:

\documentclass[tikz,border=3.14]{standalone}
\begin{document}
\begin{tikzpicture}
  \newcommand\ir{2}%Inner radius
  \newcommand\nb{5}%Number of bars
  \foreach \i in {1,...,\nb}
    {
      \draw (0,0) -- ({360*\i/\nb}:\ir);
    }
\end{tikzpicture}
\end{document}

Adding the small "T"-parts without any other manual calculations:

\documentclass[tikz,border=3.14]{standalone}
\begin{document}
\begin{tikzpicture}
  \newcommand\ir{2}%Inner radius
  \newcommand\nb{5}%Number of bars
  \foreach \i in {1,...,\nb}
    {
      \pgfmathsetmacro\ang{360*\i/\nb}
      % get the centre point of the line (0,0)--(\ang:\ir) as (tmp)
      \draw (0,0) -- coordinate(tmp) (\ang:\ir)
      % from that centre, draw perpendicular for 0.25 (+(<coord>) syntax)
            (tmp) -- +(\ang + 90:.25);
    }
\end{tikzpicture}
\end{document}

edited Sep 09 '21 at 18:07

answered Sep 09 '21 at 17:16

Skillmon

60,462

The problem in my question was just a MWE. Other than this I need to draw a line perpendicular to each of this lines (centered at the top of the line, and of arbitrary length). It is difficult to explain, it will look like a set of rotating T's. That is why I need the coordinates of the points (I think). – Daniel Duque Sep 09 '21 at 17:25
@DanielDuque see the edit. With TikZ you don't need to calculate much if you don't want to... – Skillmon Sep 09 '21 at 18:00
1

@DanielDuque For future reference, feel free to ask a complete question instead of just a small part and then ask the rest in the answer comments. A sketch of the expected output is also very appreciated to fully understand your needs. – SebGlav Sep 09 '21 at 18:10

Markus G. · Answer 2 · 2021-09-09T17:30:55.617

You can use \pgfmathsetmacro to define your variables:

\documentclass[tikz]{standalone}
\begin{document}
    \begin{tikzpicture}             
        \pgfmathsetmacro{\ir}{2}
        \pgfmathsetmacro{\nb}{5} 
        \pgfmathsetmacro{\tta}{2*pi/\nb}
    \foreach \i in {1,...,\nb} {                                             
        \pgfmathsetmacro{\ctta}{cos(deg(\i*\tta))}
        \pgfmathsetmacro{\stta}{sin(deg(\i*\tta))}  
        \pgfmathsetmacro{\ltpcx}{\ir*\ctta} 
        \pgfmathsetmacro{\ltpcy}{\ir*\stta}                                                                          
        \draw (0,0) -- (\ltpcx,\ltpcy);                           
    }                                                                  
\end{tikzpicture} 

\end{document}

EDIT For your reference, there are a couple of questions and answers that explain quite nicely the difference between pgfmathsetmacro and newcommand for use as variable in tikz:

Difference between \newcommand and \pgfmathsetmacro used in TikZ \coordinate

What is the preferred way of defining a TikZ constant?

They are not directly related to your question though.

The result of \pgfmathsetmacro\<macro>{<number-not-formula>} is pretty much the same as \newcommand\<macro>{<number-not-formula>} except that \pgfmathsetmacro takes much longer for this simple task (however for 2*pi/\nb this is better). — Skillmon, Sep 09 '21 at 17:55
Meaning your comment applies only to the initial definition of \ir and \nb in this example? — Markus G., Sep 09 '21 at 17:57
Yes, only for \ir and \nb. But the \ltpcx and \ltpcy are not really necessary, you could as well just use \draw (0,0) -- (\ir*\ctta, \ir*\stta); if those points aren't used elsewhere. — Skillmon, Sep 09 '21 at 18:03

Bernard · Answer 3 · 2021-09-10T08:09:30.897

5

A short code with pstricks and multido:

\documentclass{article}
\usepackage[svgnames]{xcolor}%
\usepackage{pst-eucl, multido}
\begin{document}
\psset{unit=1.5cm, linewidth=1pt, linecolor=SteelBlue, tbarsize=1}
\begin{pspicture}(-3,-3)(3,3) 
\multido{\I = 0+72}{5}{\psline{-|}(0,0)(3;\I)}
\end{pspicture}
\end{document}

edited Sep 10 '21 at 08:09

answered Sep 09 '21 at 21:37

Bernard

271,350

\SpecialCoor is no longer needed. It is already enabled since version x.x.x.x (I forgot). – Display Name Sep 09 '21 at 22:42
@MakeMeSmarterEveryDay: I wasn't sure, and didn't have time to check. It makes the code still shorter. Thanks for the confirmation! – Bernard Sep 10 '21 at 08:10

Draw n lines in a loop around a circle

3 Answers3