Compute the elevation of a coordinate in TikZ

I'm wracking my brains over a seemingly simple problem. Given a coordinate, I would like to do some computation with its components. More specifically, I want to compute the elevation of a point.

Consider this M(not)WE:

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\coordinate (A) at (2,3);

\newdimen\x
\newdimen\y
\pgfextractx{\x}{\pgfpointanchor{A}{center}}
\pgfextracty{\y}{\pgfpointanchor{A}{center}}
\pgfmathparse{atan2(\y,\x)}
\node at (1,1) {\pgfmathresult};
\end{tikzpicture}
\end{document}

My goal is to extract the x and the y component from the point A, compute the elevation, and print this in a node. How can I achieve this?

• Dec 4 '14 at 21:57

You can use

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\coordinate (A) at (2,3);
%
\newdimen\x
\newdimen\y
\pgfextractx{\x}{\pgfpointanchor{A}{center}}
\pgfextracty{\y}{\pgfpointanchor{A}{center}}
\node at (1,1) {\pgfmathparse{atan2(\y,\x)}\pgfmathresult};
\end{tikzpicture}
\end{document}

or

\def\myresult{\pgfmathparse{atan2(\y,\x)}\pgfmathresult}
\node at (1,1) {\myresult};

or

\pgfmathsetmacro\myresult{atan2(\y,\x)}
\node at (1,1) {\myresult};
• Thanks! One question though. Say I want to use \myresult as a coordinate in a polar coordinate, as in \node at (\myresult:1) {test};, how can I do that?
– Ingo
Apr 25 '14 at 12:23
• Nevermind, with \pgfmathsetmacro it works.
– Ingo
Apr 25 '14 at 12:26

There is a standard way to do it using let like this :

\begin{tikzpicture}
\coordinate (A) at (2,3);
\path let \p1=(A) in node{\x1};
\end{tikzpicture} And if you want it as a number (or in cm) you can see this answer.