# Intersection of double lines

I'm trying unsuccessfully to fill the intersection of two double lines with an other colour. Here is minimal working example :

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}

\node (Emetteur) at (0,0) {};
\node (Recepteur) at (2.5,0) {};
\node (Recepteur2) at (-2.5,0) {};
\node (Cible) at (1,3) {};

\draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
\draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);

\draw (-4,0) -- (4,0);
\draw (Emetteur) node {$\bullet$} node [below] {\'Emetteur};
\draw (Recepteur) node {$\bullet$} node [below] {R\'ecepeur 1};
\draw (Recepteur2) node {$\bullet$} node [below] {R\'ecepeur 2};
\draw (Cible) node {$\bullet$} node [above=0.1cm, align = center] {Cible};

\draw [blue] (Emetteur) -- (Cible) node [midway, sloped, above] {$d_1$};
\draw [red] (Cible) -- (Recepteur) node [pos = 0.5, sloped, above] {$d_2$};
\draw [green!50!black] (Cible) -- (Recepteur2) node [pos = 0.5, sloped, above] {$d_3$};

\end{tikzpicture}
\end{document}


I get the following result :

I've found a way using the opacity option :

    \draw [black!15, double = black!50, double distance = 5, opacity = 0.2] (1.25,0) ellipse (6cm and 3.025cm);
\draw [black!15, double = black!50, double distance = 5, opacity = 0.2] (-1.25,0) ellipse (6cm and 3.25cm);


Then I get :

That's just a trick since the superposition of two transparent shapes makes an other colour, but I prefer to avoid the opacity option since I get bad rendering when printing and I can't get an intersection of the colour I want.

Any clue ?

• You need the transparency group key to combine the opacity settings not leaking out if I understood this correctly. – percusse Mar 8 '15 at 12:40

You can use blending

\begin{scope}[blend group=multiply]
\draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
\draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);
\end{scope}


Full code:

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}

\node (Emetteur) at (0,0) {};
\node (Recepteur) at (2.5,0) {};
\node (Recepteur2) at (-2.5,0) {};
\node (Cible) at (1,3) {};
\begin{scope}[blend group=multiply]
\draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
\draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);
\end{scope}

\draw (-4,0) -- (4,0);
\draw (Emetteur) node {$\bullet$} node [below] {\'Emetteur};
\draw (Recepteur) node {$\bullet$} node [below] {R\'ecepeur 1};
\draw (Recepteur2) node {$\bullet$} node [below] {R\'ecepeur 2};
\draw (Cible) node {$\bullet$} node [above=0.1cm, align = center] {Cible};

\draw [blue] (Emetteur) -- (Cible) node [midway, sloped, above] {$d_1$};
\draw [red] (Cible) -- (Recepteur) node [pos = 0.5, sloped, above] {$d_2$};
\draw [green!50!black] (Cible) -- (Recepteur2) node [pos = 0.5, sloped, above] {$d_3$};

\end{tikzpicture}
\end{document}


• For different blending modes refer to pages 342 and 343 of pgfmanual version 3. – user11232 Mar 8 '15 at 12:36