Adding width of text to node coordinate?

Question

I am currently trying to position some text in the center of a square drawn in a tikzpicture, like so:

However, I am having a bit of trouble.

Take the following example:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{tikzpagenodes}
\usepackage{tikz}
\usepackage{calc}
\usepackage{layouts}

\begin{document}

\begin{tikzpicture}[overlay, remember picture, x=1cm, y=1cm]
    \newcommand{\boxWidth}{5cm};
    \newcommand{\boxHeight}{3cm};
    \newcommand{\boxPosX}{5cm};
    \newcommand{\boxPosY}{-5cm};

    \newcommand{\someText}{Hello World};
    \newcommand{\textPosX}{\boxPosX + (\printinunitsof{cm}\widthof{\someText}/2)};
    \newcommand{\textPosY}{\boxPosY + \boxHeight / 2};

    \draw [line width=0.05cm, rounded corners=.3cm, color=red] (\boxPosX,\boxPosY) rectangle ++(\boxWidth, \boxHeight);

    \node at (\textPosX, \textPosY) {\someText};
\end{tikzpicture}

\end{document}

The problem arrises when I try using the width of the text: \widthof{\someText}/2 (from the calc package). (Reference Post)

According to the same reference post, \widthof returns a length in points, which is incompatible with centimeters. Therefore, I tried converting to centimeters by using the method described here: \printinunitsof{cm}\widthof{\someText}.

However, this still yields an "Illegal unit of measure (pt inserted)."

What am I doing wrong and how can I correctly convert my units from points to centimeters?

Answer 1

From your code I sort of sense what you might want:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikzpagenodes}
\usepackage{calc}
\usepackage{layouts}

\begin{document}

\begin{tikzpicture}[overlay, remember picture, x=1cm, y=1cm]
    \newcommand{\boxWidth}{5cm};
    \newcommand{\boxHeight}{3cm};
    \newcommand{\boxPosX}{5cm};
    \newcommand{\boxPosY}{-5cm};

    \newcommand{\someText}{Hello World};
    \node[draw,line width=0.05cm, rounded corners=.3cm, color=red,
    minimum width=\boxWidth,minimum height=\boxHeight,text=black] at 
    ({\boxPosX},{\boxPosY}) {\someText};
\end{tikzpicture}

\end{document}

Instead of \newcommand use \pgfmathsetmacro to do computations, e.g. \pgfmathsetmacro{\textPosX}{\boxPosX + width("\someText")*1pt/2cm};. However, I think that all the complicated computations are unnecessary here. To put a text in the center of a box, it suffices to say \node[draw]{text}. And then you can do all sorts of spirifankerln like adding a minimum width, rounded corners etc.

Answer 2

If the text is to be placed in the centre of the rectangle, simply place it with a node midway down the path.

\draw [line width=0.05cm, rounded corners=.3cm, color=red] 
(\boxPosX,\boxPosY) rectangle ++(\boxWidth, \boxHeight)node[midway,text=black]{\someText};

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{tikzpagenodes}
\usepackage{tikz}
\usepackage{calc}
\usepackage{layouts}

\begin{document}

\begin{tikzpicture}[overlay, remember picture, x=1cm, y=1cm]
    \newcommand{\boxWidth}{5cm};
    \newcommand{\boxHeight}{3cm};
    \newcommand{\boxPosX}{5cm};
    \newcommand{\boxPosY}{-5cm};

    \newcommand{\someText}{Hello World};
   %\newcommand{\textPosX}{\boxPosX + (\printinunitsof{cm}\widthof{\someText}/2)};
   %\newcommand{\textPosY}{\boxPosY + \boxHeight / 2};

\draw [line width=0.05cm, rounded corners=.3cm, color=red] 
(\boxPosX,\boxPosY) rectangle ++(\boxWidth, \boxHeight)node[midway,text=black]{\someText};

\end{tikzpicture}

\end{document}

Answer 3

Just another way. If you have some already drawn rectangles (not nodes), you can use a fit node which encompasses rectangle corners and add a label in its center:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{tikzpagenodes}
\usepackage{tikz}
\usepackage{calc}
\usepackage{layouts}
\usetikzlibrary{fit}
\begin{document}

\begin{tikzpicture}[overlay, remember picture, x=1cm, y=1cm]
    \newcommand{\boxWidth}{5cm};
    \newcommand{\boxHeight}{3cm};
    \newcommand{\boxPosX}{5cm};
    \newcommand{\boxPosY}{-5cm};

    \newcommand{\someText}{Hello World};
%    \newcommand{\textPosX}{\boxPosX + (\printinunitsof{cm}\widthof{\someText}/2)};
%    \newcommand{\textPosY}{\boxPosY + \boxHeight / 2};

    \draw [line width=0.05cm, rounded corners=.3cm, color=red] (\boxPosX,\boxPosY) rectangle ++(\boxWidth, \boxHeight);

    \node[fit={(\boxPosX,\boxPosY) (\boxPosX+\boxWidth,\boxPosY+\boxHeight)},  label=center:\someText] {};

    \draw [line width=0.05cm, rounded corners=.3cm, color=green] (-2,-5) coordinate (1) rectangle ++(5,2) coordinate (2);

    \node[fit={(1) (2)},  label=center:\someText] {};

\end{tikzpicture}

\end{document}