Using TikZ absolute coordinates

Question

I wonder is that possible to use absolute coordinates regarding all document? Please see my example

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\filldraw[red]
(30pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\begin{tikzpicture}
\filldraw[blue]
(3pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\end{document} 

Why red and blue lines have the same left x-coordinate? I would like to move the second on 27pt left!

Answer 1

To automatically make all tikzpictures align on the origin, you can set \tikzset{every picture/.append style={trim left=0}}. This sets the left margin to be at the x position of the origin. Note that you will run into trouble if you use negative coordinates, since these will protrude out of the image. In that case, you'd have to set trim left to a negative value that is large enough to include all points.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikzset{every picture/.append style={trim left=0}}
\begin{tikzpicture}
\filldraw[red]
(30pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\begin{tikzpicture}
\filldraw[blue]
(3pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\end{document} 

Answer 2

In normal TeX there is a \phantom that is often used to leave the same amount of space as required by its arguments. You could do something similar by adding a \path (0pt,0pt) for both pictures. This ensures that the left hand side starts at the same x-coordinate:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \path (0pt,0pt);
    \draw[red] (30pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\begin{tikzpicture}
    \path (0pt,0pt);
    \draw[blue] (3pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}
\end{document} 

Answer 3

The answer is suggested by percusse. Each tikzpicture is typeset in its own box. The box is made as small as possible to typeset all what's in it. For example, a tikzpicture consisting of a square with lower left position (1,1) and upper right position (2,2) will still have a width of 1cm and a hight of 1cm.

The coordinates in your tikzpictures are completely relative to their own tikzpictures. This explains why you cannot relate the coordinates in one tikzpicture to those of another tikzpicture (unless you're using remember pictures).

Answer 4

Add a origine with a node

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \node(O) at (0,0){};
    \coordinate(O) at (0,0);
    \filldraw[red]
    (30pt, 9pt) -- (130pt, 9pt);
\end{tikzpicture}

\begin{tikzpicture}
    \node(O) at (0,0){};
    \filldraw[blue]
    (3pt, 9pt) -- (130pt, 9pt);
    \end{tikzpicture}

\end{document}