Tikz plots distorted mark

Question

Consider the following code:

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{plotmarks}
\begin{document}
  \tikz{\draw (0,0) -- plot[mark=o] (0.5,0) -- (1,0);}
\end{document}

It seems that the mark is not smoothly drawn:

Using the smooth option does not have any effects since the interpolation algorithm only affects line drawing; here the distortion occurs on the marks. Any ideas?

Answer 1

You're using the wrong syntax for plotting a point: plot (0.5,0) is assumed to be a function, so it's evaluated several times (depending on the sample number), and several instances of your point are plotted on top of each other. Fixes: Either set samples at=1 to make sure your point is only plotted once, or use the official syntax for plotting points, which is plot coordinates {(0.5,0)}

\documentclass[border=2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{plotmarks}
\begin{document}
  \tikz{\draw (0,0) -- plot[mark=o] (0.5,0) -- (1,0);}
  \tikz{\draw (0,0) -- plot[samples at={1}, mark=o] (0.5,0) -- (1,0);}
  \tikz{\draw (0,0) -- plot[mark=o] coordinates {(0.5,0)} -- (1,0);}
\end{document}