Sfdwhf

As we know that in TikZ, if unit is not mentioned in the coordinate in TikZ, it takes cm by default.

When I extract the coordinates, I was expecting the unit as cm. But TikZ shows the unit in the coordinate as pt.

How does TikZ determine the unit of measure in a coordinate if no unit is specified.

MWE:

documentclass{article}

usepackage{tikz}

usetikzlibrary{decorations.pathmorphing}

usetikzlibrary{decorations.markings}

usetikzlibrary{calc}

usetikzlibrary{positioning}

tikzset{zigzag/.style={decorate,decoration=zigzag}}

begin{document}



newdimenXCoord

newdimenYCoord

newcommand*{ExtractCoordinate}[1]{path (#1); pgfgetlastxy{XCoord}{YCoord};}



begin{tikzpicture}

  coordinate (c) at (0,-2);

  coordinate (d) at (4,-2);

  coordinate (e) at (2,-4);

  draw[thick,red,zigzag,postaction={

    decoration={

        markings,

        mark=at position 0.7 with { coordinate (x); },

        mark=at position 0.5 with { coordinate (singularity); },

    },

    decorate

  }] (-2,0) coordinate(a) -- (2,0) coordinate(b);



  draw[thick,fill=blue!20] (c) -- (b) -- (d) -- (e) -- cycle;

  draw[thick,postaction={

    decoration={

        markings,

        mark = at position 0.7 with coordinate (y);

    },

    decorate

  }] (a) -- (c);

  draw[thick,red,dashed] (x) -- (y);



  node[above = 10ex of singularity,red] (sn) {singularity};

  draw[red,->] (sn) -- ($(singularity)+(0,1)$);

  ExtractCoordinate{x};

  node[above] at (XCoord,YCoord) {(XCoord,YCoord)};

end{tikzpicture}



end{document} 

You can always convert everything from pt to cm or back by multiplying by the ratio 1pt/1cm or its inverse. (If that's not what you're after, I will be happy to remove the post.)

documentclass{article}

usepackage{tikz}

usetikzlibrary{decorations.pathmorphing}

usetikzlibrary{decorations.markings}

usetikzlibrary{calc}

usetikzlibrary{positioning}

tikzset{zigzag/.style={decorate,decoration=zigzag}}

begin{document}



newdimenXCoord

newdimenYCoord

newcommand*{ExtractCoordinate}[1]{path (#1); pgfgetlastxy{XCoord}{YCoord};}



begin{tikzpicture}

  coordinate (c) at (0,-2);

  coordinate (d) at (4,-2);

  coordinate (e) at (2,-4);

  draw[thick,red,zigzag,postaction={

    decoration={

        markings,

        mark=at position 0.7 with { coordinate (x); },

        mark=at position 0.5 with { coordinate (singularity); },

    },

    decorate

  }] (-2,0) coordinate(a) -- (2,0) coordinate(b);



  draw[thick,fill=blue!20] (c) -- (b) -- (d) -- (e) -- cycle;

  draw[thick,postaction={

    decoration={

        markings,

        mark = at position 0.7 with coordinate (y);

    },

    decorate

  }] (a) -- (c);

  draw[thick,red,dashed] (x) -- (y);



  node[above = 10ex of singularity,red] (sn) {singularity};

  draw[red,->] (sn) -- ($(singularity)+(0,1)$);

  ExtractCoordinate{x};

  node[above] at (XCoord,YCoord) {%

  (pgfmathparse{XCoord*1pt/1cm}pgfmathprintnumber{pgfmathresult},cm,%

  pgfmathparse{YCoord*1pt/1cm}pgfmathprintnumber[fixed,precision=2]{pgfmathresult},cm)};

end{tikzpicture}

end{document}