7

I have a very specific problem that needs solving: I would like to produce a shape which can be most easily thought of as a circle or an ellipsis cut out of another bigger circle: Think e.g. the apple of the Apple logo (basically a big circle with something cut out on the right).

I have tried the following fragment with the pstricks package:

\begin{psclip}{\psellipse(1.8,0)(0.8,0.6)}
  \pscircle(2.6,0){.45}
\end{psclip}

This draws an ellipsis, and inside part of a circle clipped to the shape of the ellipsis.

Is it possible to subtract or cut out some shape out of another shape with pstricks (or other)? Thanks!

  • 3
    My TikZ-solution sense is tingling. – Seamus Sep 27 '10 at 14:45
  • By the way, is TikZ the better graphics package in general? – glts Sep 27 '10 at 15:08
  • @Seamus We should have a TikZ contest one of these days. – Martin Tapankov Sep 27 '10 at 16:10
  • Related discussion: are boolean operations on TikZ shapes possible? – Richard Terrett Feb 22 '11 at 5:44
  • Incidentally, "is TikZ the better graphics package in general" is not really the right question. Rather, you should ask which graphics package produces the drawings that you want as simply as is reasonable and at the quality you like. Those parameters will vary person to person but are at least reasonably quantifiable. Making a sweeping statement isn't possible. – Loop Space Feb 25 '11 at 15:21
3

I think this does somewhat what you are looking for, using pstricks :

\pscustom[fillstyle=solid,fillcolor=yellow]{%
\psarc(0,0){2}{29}{-29}
\psarcn(2,0){1}{-105}{105}
}

The \pscustom command is quite powerful but requires care. One important point to note is that when you are gluing curves together you should remember to start one curve where the previous one ends.

I hope this helps.

Regards

  • There are a lot of good answers to choose from now. I'm giving this the underdog's thumbs-up because it was the first answer after a long silence, spot-on, and using pstricks. – glts Feb 26 '11 at 20:01
5

Thanks to Jake's answer to " How can I invert a 'clip' selection within TikZ? ", here's a way of doing what (I think) you are asking using TikZ (since you say "or other").

First, the result:

Clipped Ellipses

I wasn't sure if you wanted them filled or just drawn.

Now, the code:

\documentclass{article}
\thispagestyle{empty}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[remember picture,overlay]

% A path that follows the edges of the current page
\tikzstyle{reverseclip}=[insert path={(current page.north east) --
  (current page.south east) --
  (current page.south west) --
  (current page.north west) --
  (current page.north east)}
]

\begin{scope}
\begin{pgfinterruptboundingbox}
\path [clip] (1.5,0) circle (1) [reverseclip];
\end{pgfinterruptboundingbox}

\draw[thick] (0,0) ellipse (2 and 1);
\end{scope}
\begin{scope}
\path[clip] (0,0) ellipse (2 and 1);
\draw[thick] (1.5,0) circle (1);
\end{scope}

\begin{scope}
\begin{pgfinterruptboundingbox}
\path [clip] (1.5,-3) circle (1) [reverseclip];
\end{pgfinterruptboundingbox}

\draw[red,fill=blue,ultra thick] (0,-3) ellipse (2 and 1);
\end{scope}
\begin{scope}
\path[clip] (0,-3) ellipse (2 and 1);
\draw[red,ultra thick] (1.5,-3) circle (1);
\end{scope}

\end{tikzpicture}
\end{document}

And lastly, the explanation. Jake's answer (linked above) gives a method of doing a "reverse clip" by drawing around the whole page and then punching out the desired shape in the middle. We use this to clip the ellipse against the circle. That produces the truncated ellipse (either filled or unfilled) but we need to do some more to complete the shape. To do that, we use the same size circle that we'd clipped out and clip that against the ellipse. One could easily make all of this a single command.

The major drawback of this is that the shapes are not single paths. Where this makes a difference are in the joins: if you look very closely you'll see that the corner where the circle and ellipse meet is not perfect. This has to do with how the clipping and stroking work. The clipping path is infinitesimally thin, but the stroked path is not, so clipping against a path and then stroking the original path doesn't quite work right. To make this perfect, one would have to use fadings, or modify the clipping paths so that they were (effectively) the outside of the stroked paths. Jake's solution would readily adapt to fadings.

3

This may be a slightly simplistic answer, but I think you can do this in Tikz by "overlaying with white":

\begin{tikzpicture}
\path[fill=green,draw=none] (0,0) circle(3cm); 
\path[fill=white,draw=none] (2,0) circle(2cm); 
\end{tikzpicture}
  • BTW, Tikz takes a lot of beating, IMO – Brent.Longborough Sep 27 '10 at 19:41
  • Fair enough. But still, I'm hoping for a method that lets me produce nice outline shapes, e.g. for use in diagrams. (Apart from subtraction, intersection would be the next operation I'd like to do.) – glts Sep 28 '10 at 11:42
3
\documentclass{minimal}
\usepackage{pstricks}
\begin{document}

\begin{pspicture}(-3,-2)(4,2)
\pscustom[linecolor=red,linewidth=2pt,fillcolor=blue!30,fillstyle=solid]{
  \psarcn(4,0){2.5}{216}{144}
  \psellipticarc(0,0)(3,2){37}{323}}
\end{pspicture}

\end{document}

enter image description here

  • Careful, your arcs still need a few degrees' tweaking to perfection! – glts Feb 26 '11 at 20:04
  • sure, but it can also be done automatically by calculation ... – user2478 Feb 26 '11 at 20:10
2

A solution with tikz with two circles but I've a problem if the first path is an ellipse. I don't why but the intersections are fine but the last arc is wrong with an ellipse

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{intersections}
\thispagestyle{empty} 
\begin{document} 

\begin{tikzpicture}
\coordinate (A) at (0,-3);
\coordinate (B) at (1.5,-3); 

\path[name path=circleA] (A) circle (2); 
\path[name path=circleB] (B) circle (1); 
 \path [ name intersections={of=circleA and circleB}]
(intersection-1) coordinate (E)
(intersection-2) coordinate (F) ;
\pgfmathanglebetweenpoints{\pgfpointanchor{B}{center}}{%
                           \pgfpointanchor{E}{center}} 
\global\let\FirstAngleB\pgfmathresult 
 \pgfmathanglebetweenpoints{\pgfpointanchor{B}{center}}{%
                           \pgfpointanchor{F}{center}} 
\global\let\SecondAngleB\pgfmathresult
\pgfmathanglebetweenpoints{\pgfpointanchor{A}{center}}{%
                           \pgfpointanchor{E}{center}} 
\global\let\FirstAngleA\pgfmathresult 
 \pgfmathanglebetweenpoints{\pgfpointanchor{A}{center}}{%
                           \pgfpointanchor{F}{center}} 
\global\let\SecondAngleA\pgfmathresult

\draw[color=red,fill=blue,ultra thick] (E)   arc  (\FirstAngleB:\SecondAngleB: 1cm) arc  (\SecondAngleA:\FirstAngleA: 2cm)  ; 

\end{tikzpicture} 

\end{document} 

circle and circle

with an ellipse I try this :

\path[name path=circleA] (A) ellipse (2cm and 1cm); 
\draw[color=red,fill=blue,ultra thick] (E)   arc  (\FirstAngleB:\SecondAngleB: 1cm) arc  (\SecondAngleA:\FirstAngleA: 2cm and 1cm)  ; 

perhaps I made a mistake, but the last point is wrong. Perhaps a problem with the angles. The two points of circle are right and the intersection is fine too but ... enter image description here

0

is this what you want?

\documentclass{book}
\usepackage{pstricks-add}
\begin{document}
\begin{pspicture}(0,0)(5,5)
\psclip{\psellipse[fillstyle=solid,fillcolor=red,linestyle=none](1.8,0)(0.8,0.6)}
\pscircle[fillstyle=solid,fillcolor=blue,linestyle=none](2.6,0){.45}
\endpsclip
\end{pspicture}
\end{document}
  • No -- this is what I already have. If you could make the blue bit disappear entirely then: yes. (fillcolor=white won't work.) – glts Sep 28 '10 at 11:13
  • so pstricks won't be able (I think) to remove the portion of a circle on an ellipse except you draw it by yourself. By the way, I do not think there are many situations where mimicking a fake cut is not sufficient. – pluton Sep 28 '10 at 15:09

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