Positioning '\pic' in tikz

Question

With the code

\documentclass[tikz,convert={size=640}]{standalone}

\usetikzlibrary{positioning}
\usetikzlibrary{calc}
\usetikzlibrary{quotes}

\begin{document}
\begin{tikzpicture}[
  rect/.style={rectangle},
  sum/.style={draw,circle,minimum width=0.2cm,minimum height=0.2cm},
  dot/.style={fill,circle,inner sep=1pt,outer sep=0pt},
  pics/lowpass/.style args={#1 and #2}{
    code={
      \node[sum,"-45:-"] (-in) {};
      \node[rect,right=0.3cm of -in] (-gain) {#1};
      \node[sum,right=0.3cm of -gain] (-sum) {};
      \node[dot,right=1.25cm of -sum] (-out) {};
      \node[rect,below=0.5cm of $(-sum)!0.5!(-out)$,
            "left:#2"{font=\scriptsize,yshift=-0.25cm}] (-int) {$z^{-1}$};
      \draw[-latex] (-in) -- (-gain);
      \draw[-latex] (-gain) -- (-sum);
      \draw (-sum) -- (-out);
      \draw[-latex] (-out) |- (-int); 
      \draw[-latex] (-int) -| (-in);
      \draw[-latex] (-sum |- -int) node[xshift=-1.5pt,dot] {} -- (-sum) ; 
    }
  }
] 
  \pic (lowpass1) at (0,0) {lowpass=$k_e$ and $x_1(k)$};
  \pic[right=1cm of lowpass1-out] (lowpass2) {lowpass=$k_c$ and $x_2(k)$};
  \end{tikzpicture}
\end{document}

I produce this image

Depending on absolute and relative position the lower centered dot is shifted by 1.5pt. How can I avoid this behaviour and what is the reference point when I use relative positioning with \pic?

See http://tex.stackexchange.com/questions/302100/in-tikz-why-does-a-pic-with-a-tree-get-distorted-upon-positiong-with-e-g-right and http://tex.stackexchange.com/questions/237576/anchoring-complex-tikz-pic. — cfr, Apr 04 '16 at 22:08

score 5 · Answer 1 · answered Apr 04 '16 at 15:37

First of all, this could be considered subjective, but I find the positioning to be rather confusing. If you can, I'd use absolute positioning for all nodes, it grants some consistency.

Anyway, here's a slightly modified version of your code.

Output

enter image description here

Code

\documentclass[tikz, margin=10pt]{standalone}

\usetikzlibrary{positioning,calc,quotes}

\tikzset{
    rect/.style={rectangle},
    sum/.style={draw,circle,minimum width=0.2cm,minimum height=0.2cm},
    dot/.style={fill,circle,inner sep=1pt,outer sep=0pt},
    pics/lowpass/.style args={#1 and #2}{
        code={
          \node[sum,"-45:-"] (-in) {};
          \node[rect,right=0.3cm of -in] (-gain) {#1};
          \node[sum,right=0.3cm of -gain] (-sum) {};
          \node[dot,right=1.25cm of -sum] (-out) {};
          \node[rect,below=0.5cm of $(-sum)!0.5!(-out)$] (-int) {$z^{-1}$};
          \node[dot, below=0.55cm of -sum,label={below:\scriptsize #2}] {};
          \draw[-latex] (-in) -- (-gain);
          \draw[-latex] (-gain) -- (-sum);
          \draw (-sum) -- (-out);
          \draw[-latex] (-out) |- (-int); 
          \draw[-latex] (-int) -| (-in);
          \draw[-latex] (-sum |- -int) -- (-sum); 
        }
    }
}

\begin{document}
\begin{tikzpicture}

  \pic (lowpass1) at (0,0) {lowpass=$k_e$ and $x_1(k)$};
  \pic[right=1cm of lowpass1-out] (lowpass2) {lowpass=$k_c$ and $x_2(k)$};

\end{tikzpicture}
\end{document}

score 1 · Answer 2 · answered Apr 05 '16 at 06:05

It seems it's a bug in the interplay of the positioning library and \pic. A possible workaround is to use the center anchor of each node in the definition of the \pic:

\documentclass[tikz,convert={size=640}]{standalone}

\usetikzlibrary{positioning}
\usetikzlibrary{calc}
\usetikzlibrary{quotes}

\begin{document}
\begin{tikzpicture}[
  rect/.style={rectangle},
  sum/.style={draw,circle,minimum width=0.2cm,minimum height=0.2cm},
  dot/.style={fill,circle,inner sep=1pt,outer sep=0pt},
  pics/lowpass/.style args={#1 and #2}{
    code={
      \begin{scope}[every node/.append style={anchor=center}]
        \node[sum,"-45:-"] (-in) {};
        \node[rect,right=0.3cm of -in] (-gain) {#1};
        \node[sum,right=0.3cm of -gain] (-sum) {};
        \node[dot,right=1.25cm of -sum] (-out) {};
        \node[rect,below=0.5cm of $(-sum)!0.5!(-out)$,
              "left:#2"{font=\scriptsize,yshift=-0.25cm}] (-int) {$z^{-1}$};
        \draw[-latex] (-in) -- (-gain);
        \draw[-latex] (-gain) -- (-sum);
        \draw (-sum) -- (-out);
        \draw[-latex] (-out) |- (-int); 
        \draw[-latex] (-int) -| (-in);
        \draw[-latex] (-sum |- -int) node[dot] {} -- (-sum) ; 
      \end{scope}
    }
  }
] 
  \pic (lowpass1) at (0,0) {lowpass=$k_e$ and $x_1(k)$};
  \pic[right=1cm of lowpass1-out] (lowpass2) {lowpass=$k_c$ and $x_2(k)$};
  \end{tikzpicture}
\end{document}

this produces the desired behaviour:

Positioning '\pic' in tikz

2 Answers2

Output

Code

Linked