# Parallel Bezier Curves in TikZ

I want to use Bezier curves to draw a track in TikZ, e.g., a racetrack.

I have the centerline of the track specified with the help of Bezier curves, like this:

\documentclass[11pt]{standalone}
\usepackage{tikz}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\draw[dashed,blue] (0,0) .. controls (1,1) and (2,-1) .. (3,0);
\end{tikzpicture}
\end{document}


I now want to draw the boundary of the track which is always a distance d from the centerline.

What is the best way to achieve this?

• Welcome! You have some code which you now want to adapt. You don't know how to do it. However, you think that we, who do not have any idea what your code contains, will be able to tell you. Do you see the problem? Please edit your question to include code for a minimal document which shows the problem and which we can copy-paste-compile to produce the centreline. However, your best bet is to add double, double distance=<width between lines>, line width=<width of each line> etc. to the existing path. – cfr Jan 18 '17 at 2:44
• Sorry I was a bit lazy. Thanks for your great answer! – miga89 Jan 18 '17 at 2:58
• Thanks for editing. Could you post your answer as an answer? It doesn't make sense to have it in the question. – cfr Jan 18 '17 at 3:03

As @cfr pointed out, this is easily achievable with the double distance key. Hence, the following code achieves what I want:

\documentclass[11pt]{standalone}
\usepackage{tikz}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}

\draw[solid,red,double distance=10pt] (0,0) .. controls (1,1) and (2,-1) .. (3,0);
\draw[dashed,blue] (0,0) .. controls (1,1) and (2,-1) .. (3,0);

\end{tikzpicture}

\end{document} • @cfr: Any idea how to get rid of these small gray lines at the start and end of the border? – miga89 Jan 24 '17 at 6:43