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I constructed a graph by means of a loglogaxis with

xmin=5e0,
xmax=1e4,
ymin=1e-16,
ymax=1e0

and am trying to make an annotation by means of a circle. For this, I use

\draw[color=red] (axis cs:4e2,1e-12) circle (1);

. Unfortunately, I do not get a circle but an ellipse. I guess the \draw command is using the logarithmic axes for the radius in some way.

I just want a simple 'normal' circle for my annotation. How do I do this in the loglogaxis?

MWE:

\documentclass{standalone}
\usepackage{pgfplots}
\begin{document}
    \begin{tikzpicture}
        \begin{loglogaxis}
        [
            xmin=5e0,
            xmax=1e4,
            ymin=1e-16,
            ymax=1e0
        ]
            \addplot table
            {
                20 1e-12
                700 1e-9
                6000 1e-3
            };
            \draw[color=red] (axis cs:4e2,1e-12) circle (1);
        \end{loglogaxis}
    \end{tikzpicture}
\end{document}
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4  
Could you please post a complete MWE so I can play with an idea I had and see if it works? –  JLDiaz Jun 16 at 8:53

1 Answer 1

up vote 5 down vote accepted

The trick is to use absolute units for the circle radius:

\documentclass{standalone}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{loglogaxis}[
    xmin=5e0,
    xmax=1e4,
    ymin=1e-16,
    ymax=1e0
]
\addplot table {
20  1e-12
700  1e-9
6000 1e-3
};
\draw[color=red] (axis cs:4e2,1e-12) circle (1mm);
\end{loglogaxis}
\end{tikzpicture}
\end{document}

Result

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