How can I prevent pgfplots from rendering lines incorrectly when I use “no markers”?

Question

I plot tabular data wherein none of the y-values of the data go above 1.0. In the resulting plot, however, there are a couple of peaks that go beyond 1.0, giving a false impression about those data points:

This is not visible when I plot with marks, but I need to use "no marks" because it is otherwise far too busy (80 points in a small plot).

How can I prevent this?

Update: Per Jake's request, here's a minimal example that shows the described behaviour:

\documentclass{article}
\usepackage{pgfplots}
\begin{document}
    \begin{figure}[ht]
        \begin{tikzpicture}
            \begin{axis}[no markers, grid=major]
                \addplot coordinates{(0, 0.0000000000)
                                     (1, 0.8823529412)
                                     (2, 0.8750000000) 
                                     (3, 1.0000000000) 
                                     (4, 0.8666666667)
                                     (80, 0.0000000000)}[thick];
            \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}

The problem is less pronounced when I don't make my lines thick, but it is still there (and I want thick lines).

Answer 1

There are a couple of ways you can avoid this: You can either tell pgfplots to use round corners or beveled corners for all corners by supplying the option line join=round or line join=bevel to the axis or to individual plots, or you can lower the threshold for when the join type changes from mitered to beveled by using miter limit=<value> (10 is the default).

\documentclass{article}
\usepackage{pgfplots}
\begin{document}
    \begin{figure}[ht]
        \begin{tikzpicture}
            \begin{axis}[no markers,grid=major,every axis plot post/.append style={thick}]
                \addplot  coordinates{(0, 0.0) (0, 0.9) (1, 0.9) (2, 1) (3, 0.9) (80, 0)};
                \addplot +[line join=round] coordinates{(0, 0.0) (0, 0.9) (2, 0.9) (3, 1) (4, 0.9) (80, 0)};
                \addplot +[line join=bevel] coordinates{(0, 0.0) (0, 0.9) (3, 0.9) (4, 1) (5, 0.9) (80, 0)};
                \addplot +[miter limit=5] coordinates{(0, 0.0) (0, 0.9) (4, 0.9) (5, 1) (6, 0.9) (80, 0)};
            \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}