How to import ASCII coordinates to TikZ

Question

I have a long file of Brazil coordinates like:

(-3.43,-0.56) -- (-3.44,-0.56) -- (-3.44,-0.55) -- (-3.50,-0.55) -- (-3.52,-0.55) ...

and I want to import then into a tikzpicture environment to use with the \draw command. Some thing like this:

\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\pagestyle{empty}

\begin{tikzpicture}
\draw 'myfile'
\end{tikzpicture}

\end{document}

Answer 1

You can read the content of a file in an expandable way using TeX's \input, which however is renamed to \@@input by LaTeX in order to provide a higher level \input. The \draw command (actually \path) of TikZ will expand the following tokens first before looking for the coordinates.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \makeatletter
    \draw\@@input coordfile ;
    \makeatother
\end{tikzpicture}
\end{document}

Here I assume the coordinates are in coordfile.tex or coordfile (no extension). You should add a trailing space after the filename and avoid filenames with special, i.e. non-English characters and of course spaces.

---

If you need this more than once you should declare a different name for \@@input in the preamble and use this in the body instead:

\documentclass{article}
\usepackage{tikz}
\makeatletter
\let\expinput\@@input
\makeatother
\begin{document}
\begin{tikzpicture}
    \draw\expinput coordfile ;
\end{tikzpicture}
\end{document}

or, more LaTeX'ish:

\documentclass{article}
\usepackage{tikz}
\makeatletter
\newcommand*\expinput[1]{\@@input #1 }
\makeatother
\begin{document}
\begin{tikzpicture}
    \draw\expinput{coordfile};
\end{tikzpicture}
\end{document}

Answer 2

You can read from files in TeX. Presume you have a file foo with content (0,0) -- (2,0) -- (2,2) Then you can read that line and pass it to a draw command as follows:

\documentclass{article}
\usepackage{tikz}
\begin{document}
  \newread\bar
  \openin\bar=foo
  \read\bar to\res
  \tikz\draw\res;
\end{document}

And that will draw the corresponding lines. If you have multiple lines in a file then \read\bar to \res a second time will read the second line from the file. After you are done with it, you should \closein\bar. There is also an \ifeof which you can use to loop over the file until it contains no more lines.

To go through the entire file, you can simply write a macro that loops as long as there are things to read. For this simple setup to work, the first command in the loop has to be the read of the file.

\documentclass{article}
\usepackage{tikz}
\def\myloop#1#2#3\repeat{\def\filenm{#2}\def\body{#1#2#3}\iterate}
\def\iterate{\body\ifeof\filenm\let\next\relax\else\let\next\iterate\fi\next}
\begin{document}
\newread\bar
\openin\bar=foo
\begin{tikzpicture}
  \myloop\read\bar to\res\draw\res;\repeat
\end{tikzpicture}
\end{document}

This will add every line of the file to the same tikzpicture.