9

I am searching for a macro which prints the current x-unit-length. For instance the following document:

\documentclass[border=2pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

  \begin{tikzpicture}[x=2cm,y=3cm]
    \node at (0,0) {};
  \end{tikzpicture}
\end{document}

Now I want a macro which can return the '2cm' of 'x' or '3cm' of y.

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1
  • Considere accepting one of the answers or no one is convenient? – Tarass Apr 4 '18 at 18:07
8

Here is a solution using the calc library:

\documentclass[border=2pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}

\def\getxlengthincm#1{
  \path let \p{x}=(1,0), \n{xlencm}={scalar(veclen(\x{x},\y{x})/1cm)}
  in \pgfextra{\xdef#1{\n{xlencm}}};
}

\begin{document}
\begin{tikzpicture}[x=2cm,y=3cm]
  \getxlengthincm{\myxlength}
  \node[align=center] at (0,0) {x length:\myxlength cm};
\end{tikzpicture}
\end{document}

enter image description here

Here is a variant with explicit pt unit:

\def\getxlength#1{
  \path let \p{x}=(1,0), \n{xlen}={veclen(\x{x},\y{x})}
  in \pgfextra{\xdef#1{\n{xlen}}};
}
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7
  • Why not simply use \path let \p{x}=(1,0), \n{xlencm}={scalar(\x{x}/1cm)} without veclen ? – Kpym Apr 4 '18 at 13:51
  • @Kpym the value of x (and y) can be a length or a coordinate. – Paul Gaborit Apr 4 '18 at 13:54
  • I also want the unit, so, cm to be retrieved. Here you added it as text. – Arne Apr 4 '18 at 14:15
  • @PaulGaborit you use it here with \p{x}=(1,0) so veclen(\x{x},\y{x}) and \x{x} are the same, no ? – Kpym Apr 4 '18 at 14:30
  • @Kpym Try with x={(1cm,1cm)} for example... – Paul Gaborit Apr 4 '18 at 14:41
5

Using the printlen package and https://tex.stackexchange.com/a/15996/36296

\documentclass[border=2pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{printlen}

\newlength{\pgfx}
\newlength{\pgfy}

\uselengthunit{cm}
\begin{document}

  \begin{tikzpicture}[x=2cm,y=3cm]
    \node at (0,0) {};
    \pgfpointxy{1}{1};
    \makeatletter
    \setlength{\pgfx}{\pgf@x}
    \setlength{\pgfy}{\pgf@y}
    \makeatother
    \node {\printlength{\pgfx}~\printlength{\pgfy}}; 
  \end{tikzpicture}
\end{document}

enter image description here

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6
  • 1
    So there is no simple, native macro which can do this. Feels a bit weird to me ;) – Arne Apr 4 '18 at 12:00
  • @Arne I did not say that, just that you could do it like this – samcarter_is_at_topanswers.xyz Apr 4 '18 at 12:01
  • If I replace y=3cm by y={(-2cm,1cm)}, I got a wrong result! – Paul Gaborit Apr 4 '18 at 13:53
  • What does y={(-2cm,1cm)} mean? I thought y is a coordinate... – Arne Apr 4 '18 at 14:17
  • 2
    @Arne x defines the x-vector. You can use x=1cm (equivalent to x={(1cm,0)}) or a true vector as x={(1cm,5mm)} (see pp.357-358, pgfmanual, v3.0.1a). – Paul Gaborit Apr 4 '18 at 14:51
4

enter image description here

\documentclass[border=2pt]{standalone}

\usepackage{tikz,luatex85,siunitx}

\makeatletter
\newcommand{\NodeDist}[3][\MyDist]{%
    \pgfpointdiff{\pgfpointanchor{#2}{center}}
                 {\pgfpointanchor{#3}{center}}
    % no need to use a new dimen
    \pgf@xa=\pgf@x
    \pgf@ya=\pgf@y
    % to convert from pt to cm   
    \pgfmathparse{veclen(\pgf@xa,\pgf@ya)/28.45274}
    \global\let#1\pgfmathresult % we need a global macro    
}

\newcommand{\TZUnits}{
    \coordinate (@0) at (0,0) ;
    \coordinate (@X) at (1,0) ;
    \coordinate (@Y) at (0,1) ;
    \NodeDist[\Xunit]{@0}{@X}\edef\Xunit{\SI{\Xunit}{\cm}}
    \NodeDist[\Yunit]{@0}{@Y}\edef\Yunit{\SI{\Yunit}{\cm}}
}

\makeatother

\begin{document}

  \begin{tikzpicture}[x=2cm,y=3cm]
    \TZUnits
    \node {\Xunit~\Yunit}; 
  \end{tikzpicture}

\end{document}
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2
  • Here, also the unit (cm) is missing. – Arne Apr 4 '18 at 14:16
  • Vos désirs font désordre... – Tarass Apr 4 '18 at 14:53

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