[Tex/LaTex] pgfplots – dotted line style – why square dots


When using dotted line style in a pgfplot, I realised that the dots are really square dots.

enter image description here

Usually most people associate dot with a filled circle(or is it just me?). And I know that there are workarounds to get the 'real dotted' line style.
I am curious to know why pgfplot associates dot with a square dot, by default, in line style.

Here is source for the above figure:

  xlabel= $x$,
  ylabel= $y$,
  ymax = 6,
  legend columns=-1,
\addplot[mark=none, black, dotted] coordinates {(0,2) (5,2)};
\addplot[mark=none, black,thick, dotted] coordinates {(0,3) (5,3)};
\addplot[mark=none, black, very thick,dotted] coordinates {(0,4) (5,4)};
\addplot[mark=none, black, ultra thick,dotted] coordinates {(0,5) (5,5)};

\node at (axis cs:2.5, 1.8){default};
\node at (axis cs:2.5, 2.8){thick};
\node at (axis cs:2.5, 3.8){very thick};
\node at (axis cs:2.5, 4.8){ultra thick};


Best Answer

This is not a TeX or any TeX package issue but how PDF specifications are defined. pgfplots relies on TikZ and TikZ relies on PS/PDF instructions that are finally used inside the end result.

Dotted and dash-dotted lines are short lines drawn on and off very much like a TikZ decoration. For example if you add line cap=round you see the difference.