Tikz spy connection path double line pgf layer problem

Question

I am using the spy library of the tikz package in order to magnify a part of an image. However, since my image is multicolored, I would like to use a double line to improve the contrast marking the magnified area. Here is a MWE illustrating my problem:

\documentclass{article}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{spy, shapes.geometric}
\begin{document}
\begin{tikzpicture}[

spy using outlines={ellipse, size=5.5cm, height=3cm, connect spies, every spy on node/.append style={double, line width=1pt}}
]
\node[anchor=south west, inner sep=0pt] (image) at (0,0)
    {\includegraphics[width=.6\textwidth]{example-image-a}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \coordinate (target point) at (0.4,0.3);
        \coordinate (magnified result) at (0.7,-0.5);
        \spy[red, magnification=3, spy connection path={
            \draw[red, double, line width=1pt] (tikzspyonnode) -- (tikzspyinnode);
        }] on (target point) in node [double distance = 2pt, line width=2pt, fill=white] at (magnified result);
    \end{scope}
\end{tikzpicture}
\end{document}

Here is the output that this code produces:

As you can see, the connection line appears on top of the ovals, which makes it look messy.

I would like to have the connection line under the ovals. So I modified my code as follows:

\documentclass{article}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{spy, shapes.geometric}
\pgfdeclarelayer{connection}
\pgfsetlayers{connection,main}  % set the order of the layers (main is the standard layer)
\begin{document}
\begin{tikzpicture}[
  spy using outlines={ellipse, size=5.5cm, height=3cm, connect spies, every spy on node/.append style={double, line width=1pt}},
]
\node[anchor=south west, inner sep=0pt] (image) at (0,0)
    {\includegraphics[width=.6\textwidth]{example-image-a}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \coordinate (target point) at (0.4,0.3);
        \coordinate (magnified result) at (0.7,-0.5);
        \spy[red, magnification=3, spy connection path={
            \begin{pgfonlayer}{connection}
                \draw[red, double, line width=1pt] (tikzspyonnode) -- (tikzspyinnode);
            \end{pgfonlayer}
        }] on (target point) in node [double distance = 2pt, line width=2pt, fill=white] at (magnified result);
    \end{scope}
\end{tikzpicture}
\end{document}

This places the connection line under the ovals, however it also places it under the image.

How could I place the connection line above the image, but under the ovals? Any help would be appreciated.

Please consider accepting the provided answer if it solved the problem. The same is true for some of your other questions. — Dr. Manuel Kuehner, Jun 08 '21 at 01:47

score 3 · Accepted Answer · 2021-05-05T17:25:22.927

There exist some styles that allow you to put a node on a specific layer. You can use those.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{spy, shapes.geometric}
\makeatletter
\pgfkeys{% https://tex.stackexchange.com/a/20426
  /tikz/on layer/.code={
    \pgfonlayer{#1}\begingroup
    \aftergroup\endpgfonlayer
    \aftergroup\endgroup
  },
  /tikz/node on layer/.code={
    \gdef\node@@on@layer{%
      \setbox\tikz@tempbox=\hbox\bgroup\pgfonlayer{#1}\unhbox\tikz@tempbox\endpgfonlayer\egroup}
    \aftergroup\node@on@layer
  },
  /tikz/end node on layer/.code={
    \endpgfonlayer\endgroup\endgroup
  }
}
\def\node@on@layer{\aftergroup\node@@on@layer}
\makeatother
\pgfdeclarelayer{connection}
\pgfdeclarelayer{spies}
\pgfsetlayers{main,connection,spies}  % set the order of the layers (main is the standard layer)
\begin{document}
\begin{tikzpicture}[
  spy using outlines={ellipse, size=5.5cm, height=3cm, connect spies, 
  every spy on node/.append style={double, line width=1pt}},
]
\node[anchor=south west, inner sep=0pt] (image) at (0,0)
    {\includegraphics[width=.6\textwidth]{example-image-a}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \coordinate (target point) at (0.4,0.3);
        \coordinate (magnified result) at (0.7,-0.5);
        \spy[red, magnification=3, spy connection path={
           \draw[red, double, line width=1pt,on layer=connection,
           postaction={draw,line width=1pt,white,on layer=spies}] (tikzspyonnode) -- (tikzspyinnode);
        }] on (target point) in node 
        [node on layer=spies,
            double distance = 2pt, line width=2pt, fill=white,draw=red] 
            at (magnified result);
    \end{scope}
\end{tikzpicture}
\end{document}

I also added a postaction to have the white lines connected as well.

Of course, one can repeat the trick for the smaller node.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{spy, shapes.geometric}
\makeatletter
\pgfkeys{% https://tex.stackexchange.com/a/20426
  /tikz/on layer/.code={
    \pgfonlayer{#1}\begingroup
    \aftergroup\endpgfonlayer
    \aftergroup\endgroup
  },
  /tikz/node on layer/.code={
    \gdef\node@@on@layer{%
      \setbox\tikz@tempbox=\hbox\bgroup\pgfonlayer{#1}\unhbox\tikz@tempbox\endpgfonlayer\egroup}
    \aftergroup\node@on@layer
  },
  /tikz/end node on layer/.code={
    \endpgfonlayer\endgroup\endgroup
  }
}
\def\node@on@layer{\aftergroup\node@@on@layer}
\makeatother
\pgfdeclarelayer{connection}
\pgfdeclarelayer{spies}
\pgfsetlayers{main,connection,spies}  % set the order of the layers (main is the standard layer)
\begin{document}
\begin{tikzpicture}[
  spy using outlines={ellipse, size=5.5cm, height=3cm, connect spies, 
  every spy on node/.append style={node on layer=spies,double,draw=red, line width=1pt}},
]
\node[anchor=south west, inner sep=0pt] (image) at (0,0)
    {\includegraphics[width=.6\textwidth]{example-image-a}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \coordinate (target point) at (0.4,0.3);
        \coordinate (magnified result) at (0.7,-0.5);
        \spy[red, magnification=3, spy connection path={
           \draw[red, double, line width=1pt,on layer=connection,
           postaction={draw,line width=1pt,white,on layer=spies}] (tikzspyonnode) -- (tikzspyinnode);
        }] on (target point) in node 
        [node on layer=spies,draw=red,
        double distance = 2pt, line width=2pt, fill=white] 
            at (magnified result);
    \end{scope}
\end{tikzpicture}
\end{document}

Awesome! Thank you so much for your reply! I haven't figured out your entire code yet, but I was wondering a similar fix could be employed for the connection with the smaller oval. Currently there is a red line going through it. — jopeto, May 05 '21 at 17:17
@jopeto Sure. I added that, too. I agree that this looks better. — , May 05 '21 at 17:25

Tikz spy connection path double line pgf layer problem

1 Answers1