Krdytkyu

Is there a non scalable unit in tikz?

I have the following picture,

    documentclass{report}

    usepackage{tikz}

    begin{document}

    begin{tikzpicture}[>=latex, scale=2]

    draw[->] (0,0) -- (2,1);

    filldraw   (0,0) circle[radius=0.05cm] node[anchor=north] {$P$}

                (2,1) circle[radius=0.05cm] node[anchor=north] {$Q$};

    end{tikzpicture}

    end{document}

Some elements, like the line width, the arrowheads or the text aren't affected by the scale=2 option. I would like the circles to behave in the same fashion. Is this possible? I tried using different units for the circle radius (cm, pt, em) but I had no luck.

You could use a node instead of a circle. nodes don't scale either:

 documentclass{report}

    usepackage{tikz}

    begin{document}

    begin{tikzpicture}[>=latex, scale=2]

    draw[->] (0,0) -- (2,1);

    filldraw   (0,0) node[circle,inner sep=0.025cm,fill=black]{} node[anchor=north] {$P$}

                (2,1) circle[radius=0.05cm] node[anchor=north] {$Q$};

    end{tikzpicture}

    end{document}

Yes, scale really scales mainly distances, not line widths etc. UPDATE: I misread the question, sorry, and big thanks to Paul Paulsen for pointing this out. You can just divide out the scale factor in the circle radii.

documentclass{report}

usepackage{tikz}

begin{document}

begin{tikzpicture}[>=latex, scale=2]

pgfgettransformentries{myscale}{tmp}{tmp}{tmp}{tmp}{tmp}

draw[->] (0,0) -- (2,1);

filldraw   (0,0) circle[radius=0.05cm/myscale] node[anchor=north] {$P$}

            (2,1) circle[radius=0.05cm/myscale] node[anchor=north] {$Q$};

end{tikzpicture}

begin{tikzpicture}[>=latex]

draw[->] (0,0) -- (2,1);

filldraw   (0,0) circle[radius=0.05cm] node[anchor=north] {$P$}

            (2,1) circle[radius=0.05cm] node[anchor=north] {$Q$};

end{tikzpicture}

end{document}

ORIGINAL ANSWER: Here I address how one can scale the line width with the distances. Note that I do not recommend using pgflowlevelsynccm here as it screws up the bounding box (which is why there are vspaces added), but I list it for completeness.

documentclass{report}

usepackage[margin=1in]{geometry}

usepackage{tikz}

begin{document}

subsection*{Original post}

begin{tikzpicture}[>=latex, scale=2]

draw[->] (0,0) -- (2,1);

filldraw   (0,0) circle[radius=0.05cm] node[anchor=north] {$P$}

            (2,1) circle[radius=0.05cm] node[anchor=north] {$Q$};

end{tikzpicture}



subsection*{Using texttt{textbackslash pgflowlevelsynccm}}



vspace*{2cm}

begin{tikzpicture}[>=latex, scale=2]

pgflowlevelsynccm

draw[->] (0,0) -- (2,1);

filldraw   (0,0) circle[radius=0.05cm] node[anchor=north] {$P$}

            (2,1) circle[radius=0.05cm] node[anchor=north] {$Q$};

end{tikzpicture}

vspace*{1cm}



subsection*{Reading out transformation and applying it to lines etc.}

begin{tikzpicture}[>=latex, scale=2]

pgfgettransformentries{myscale}{tmp}{tmp}{tmp}{tmp}{tmp}

draw[->,line width=myscale*pgflinewidth] (0,0) -- (2,1);

filldraw[,line width=myscale*pgflinewidth]   

(0,0) circle[radius=myscale*0.05cm] node[anchor=north] {$P$}

            (2,1) circle[radius=myscale*0.05cm] node[anchor=north] {$Q$};

end{tikzpicture}





subsection*{Reading out transformation and applying it to lines etc. (2)}

begin{tikzpicture}[>=latex, scale=2]

pgfgettransformentries{myscale}{tmp}{tmp}{tmp}{tmp}{tmp}

draw[->,line width=myscale*pgflinewidth] (0,0) -- (2,1);

filldraw[,line width=myscale*pgflinewidth]   

(0,0) circle[radius=myscale*0.05cm] node[below=myscale*0.05cm] {$P$}

            (2,1) circle[radius=myscale*0.05cm] node[above=myscale*0.05cm] {$Q$};

end{tikzpicture}



subsection*{Reading out transformation and applying it to lines etc. (3)}

begin{tikzpicture}[>=latex, scale=2,transform shape]

pgfgettransformentries{myscale}{tmp}{tmp}{tmp}{tmp}{tmp}

draw[->,line width=myscale*pgflinewidth] (0,0) -- (2,1);

filldraw[,line width=myscale*pgflinewidth]   

(0,0) circle[radius=myscale*0.05cm] node[below=myscale*0.05cm] {$P$}

            (2,1) circle[radius=myscale*0.05cm] node[above=myscale*0.05cm] {$Q$};

end{tikzpicture}



end{document}

And I would draw the thing probably like this:

documentclass[tikz,border=3.14mm]{standalone}

begin{document}

begin{tikzpicture}[>=latex, scale=2,bullet/.style={transform shape,inner

sep=0.05cm,fill,circle}]

pgfgettransformentries{myscale}{tmp}{tmp}{tmp}{tmp}{tmp}

draw[->,shorten >=2pt,line width=myscale*pgflinewidth] 

(0,0) node[bullet,label=below:$P$]{}

   --         (2,1) node[bullet,label=below:$Q$]{};

end{tikzpicture}



end{document}