position node relative to current bounding box

Question

With

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}

\draw (2,2) circle (3cm);

\node at (current bounding box.north)[anchor=north]{north};
\node at (current bounding box.north west)[anchor=north west]{north west};
\node at (current bounding box.north east)[anchor=north east]{north east};

\end{tikzpicture}
\end{document}

one can position a node relative to the bounding box of the picture, using a set of given positions (north, north west, etc.).

I would like to position the text more freely within the current bounding box, e.g., at position (0.45, 0.7), where (0, 0) is the lower left and (1, 1) the top right corner of the current bounding box.

How to achieve this?

Answer 1

You can calculate the coordinate using the calc library. Note that if you place nodes near the edge that sticks outside, the current bounding box node will change. If you don't want the bounding box to be changed you can add a \useboundingbox as in the below example.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\newcommand\relcoord[2]{({$(current bounding box.south west)!#1!(current bounding box.south east)$} |- {$(current bounding box.south west)!#2!(current bounding box.north west)$})}
\begin{document}
\begin{tikzpicture}

\draw (2,2) circle[radius=2.5cm];

\node at (current bounding box.north)[anchor=north]{north};
\node at (current bounding box.north west)[anchor=north west]{north west};
\node at (current bounding box.north east)[anchor=north east]{north east};

\useasboundingbox \relcoord{0}{0} rectangle \relcoord{1}{1};

\draw [use as bounding box,help lines,step=0.5cm] \relcoord{0}{0} grid \relcoord{1}{1};

\fill [red] \relcoord{0.6}{0.7} circle[radius=3pt];
\fill [blue] \relcoord{0.3}{0.4} circle[radius=3pt];

\foreach \x in {0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1} {
 \node at \relcoord{\x}{0.7}[anchor=center] {x};
 \node at \relcoord{0.7}{\x}[anchor=center] {x};
}
\end{tikzpicture}
\end{document}