tikz — scaling of arrows

Question

I declare a new arrow in TikZ via:

\pgfarrowsdeclarecombine{combined}{combined}{latex}{latex}{|}{|}

In the first example you see that the left left arrow doesn't end at the coordinate (0,0). How can I avoid this? Next to the first picture you see an example of PSTricks which represented the correct output.

In the second example the arrow produced by tikz looks weird.

%need latex->ps-pdf or xelatex

\documentclass{article}
\parindent0pt
\usepackage{tikz}
\usepackage{pstricks}
\usetikzlibrary{decorations.markings,arrows,calc}
\begin{document}
\par
First example
\par
\begin{tikzpicture}
\pgfarrowsdeclarecombine{combined}{combined}{latex}{latex}{|}{|}%
\draw[decoration={markings,%
                   mark=at position 0 with {\arrowreversed[scale=1]{combined}},
                   mark=at position 1 with {\arrow[scale=1]{combined}},
                   },
    postaction={decorate},line width=3pt,blue] (0,0)  -- (3,0);

\draw[yellow,line width=2pt] (0,0)  -- (3,0);
\end{tikzpicture}
\begin{pspicture}(0,0)(3,1)
 \psline[arrowscale=1.25,linecolor=blue,linewidth=3pt,arrowinset=0]{|<->|}(0,0)(3,0)
 \psline[linecolor=yellow,linewidth=2pt](0,0)(3,0)
\end{pspicture}
\par\kern1cm
Second example
\par
\begin{tikzpicture}
\pgfarrowsdeclarecombine{combined}{combined}{latex}{latex}{|}{|}%
\draw[red,line width=3pt,combined-combined] (0,0)  -- (3,0);
\draw[yellow,line width=2pt] (0,0)  -- (3,0);
\end{tikzpicture}
\begin{pspicture}(0,0)(3,1)
 \psline[linecolor=red,linewidth=3pt,arrowinset=0]{|<->|}(0,0)(3,0)
 \psline[linecolor=yellow,linewidth=2pt](0,0)(3,0)
\end{pspicture}
\end{document}

Answer 1

In the pgfmanual p.612 and p.615, this problem is directly addressed. You can simply add an offset to the inner arrow placement via

\pgfarrowsdeclarecombine[-1\pgflinewidth]{combined}{combined}{latex}{latex}{|}{|}

which seems to be working for your examples. But play around with the offset value for further adjustment. Also note that the latex arrow has a rather long tip so it looks like it is misplaced but change the offset to -1.3 and you will see that it is not.