Graphics, Figures & Tables ⇒ 'Clipped' sine curve in PGFPlots

[europaflyer]

Hi,

I'm trying to produce a sine curve in pgfplots where the y-values do not exceed a certain number like this:

sinus-wave-signal.jpg (51.58 KiB) Viewed 13415 times

Any ideas, or is this impossible?

Thanks!

[Stefan Kottwitz]

Hi,

welcome to the board!

I understand, that your question is specifically about the clipping. Could you post the code for the curve which you already have, i.e. a minimal working example?

Stefan

[europaflyer]

Here it is.

Code: Select all

\documentclass{report}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
 	\begin{axis}[
		domain=-6.283:6.283,
		grid=both,minor tick num=2,
		title={\underline{Title goes here}},
		xlabel=Bacon,
		ylabel=Eggs,
		legend pos=outer north east]
 	\addplot+[no marks, samples=100] {sin(deg(x))}; 
 	\legend{Test}
 	\end{axis}
\end{tikzpicture}
\end{document}

[svend_tveskaeg]

Read the page about a minimal working example, please. You have not produced such a thing.

[europaflyer]

Sorry! I've edited it - is that OK now?

Thanks

[Stefan Kottwitz]

Nice that you completed your example. Here just a few lines were missing, in other cases it might be less obvious how to get it compilable. I gladly test a complete example, so here's a possible solution - add a clipping path by \clip such as by

Code: Select all

\pgfplotsextra{%
   \clip (axis cs:-6.3,-0.8) rectangle (axis cs:6.3,0.8);}

Complete example:

Code: Select all

\documentclass{report}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
      domain=-6.283:6.283,
      grid=both,minor tick num=2,
      title={\underline{Title goes here}},
      xlabel=Bacon,
      ylabel=Eggs,
      legend pos=outer north east]
    \pgfplotsextra{%
    \clip (axis cs:-6.3,-0.8) rectangle (axis cs:6.3,0.8);}
    \addplot+[no marks, samples=100] {sin(deg(x))};
    \legend{Test}
  \end{axis}
\end{tikzpicture}
\end{document}

clipped-plot.png (13.53 KiB) Viewed 13384 times

For better viewing when adjusting the clipping area, you could simply replace \clip by \draw[fill,opacity=0.2]:

opacity-plot.png (14.89 KiB) Viewed 13383 times

Stefan

[europaflyer]

That's really nice work, big thanks Stefan.

Would there be any way to connect the ends by a straight line as in the example, or is the best way to manually enter four new lines (not a very elegant solution!)?

[Stefan Kottwitz]

You can draw the lines yourself doing some math, so you get it exact. The key is to use asin (arcsin) and rad to reverse the y value for getting one x value, and using the periodicity of the sinus for all the other x values.

Code: Select all

\documentclass{report}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
      domain=-6.283:6.283,
      grid=both,minor tick num=2,
      title={\underline{Title goes here}},
      xlabel=Bacon,
      ylabel=Eggs,
      legend pos=outer north east]
    \pgfplotsextra{%
      \clip (axis cs:-6.3,-0.8) rectangle (axis cs:6.3,0.8);
      \pgfmathparse{rad(asin(0.8))}\let\xa\pgfmathresult
      \pgfmathparse{pi-\xa}\let\xb\pgfmathresult
      \draw[thick] (axis cs:\xa,0.8) -- (axis cs:\xb,0.8);
      \pgfmathparse{\xa-2*pi}\let\xa\pgfmathresult
      \pgfmathparse{\xb-2*pi}\let\xb\pgfmathresult
      \draw[thick] (axis cs:\xa,0.8) -- (axis cs:\xb,0.8);
      \pgfmathparse{\xa+pi}\let\xa\pgfmathresult
      \pgfmathparse{\xb+pi}\let\xb\pgfmathresult
      \draw[thick] (axis cs:\xa,-0.8) -- (axis cs:\xb,-0.8);
      \pgfmathparse{\xa+2*pi}\let\xa\pgfmathresult
      \pgfmathparse{\xb+2*pi}\let\xb\pgfmathresult
      \draw[thick] (axis cs:\xa,-0.8) -- (axis cs:\xb,-0.8);
    }
    \addplot+[no marks, samples=100] {sin(deg(x))};
    \legend{Test}
  \end{axis}
\end{tikzpicture}
\end{document}

clipped-continuous-plot.png (13.81 KiB) Viewed 13379 times

Stefan

[feuersaenger]

Hi,

Pgfplots has two different types of clipping: the first is the graphical clipping operation which is activated by \clip, the second is based on coordinate value manipulation, more precisely by restrict y to domain*:

Code: Select all

    \documentclass{report}
    \usepackage{pgfplots}
    \begin{document}
	\thispagestyle{empty}
    \begin{tikzpicture}
      \begin{axis}[
          domain=-6.283:6.283,
          grid=both,minor tick num=2,
          title={\underline{Title goes here}},
          xlabel=Bacon,
          ylabel=Eggs,
		  restrict y to domain*=-0.8:0.8,
          legend pos=outer north east]
        \addplot+[no marks, samples=100] {sin(deg(x))};
        \legend{Test}
      \end{axis}
    \end{tikzpicture}
    \end{document}

P.png (20.9 KiB) Viewed 13373 times

The Asterisk after restrict y to domain means that *if* some sample exceeds the limit, it will be replaced by the limit. Without the asterisk, exceeding coordinate values will be discarded.

Kind regards

Christian

[Stefan Kottwitz]

Thanks Christian!

I hoped I bridged the time well until you arrived.

Stefan