Graphics, Figures & Tables ⇒ intersections

[kent]

In PGF it is easy to let PGF find the intersection between two defined lines or intersections between one circle and a line etc.
Are there any construct in PGF, or does it exist any macro, which gives intersection between an ellipses and a line say?
Kent Holing
NORWAY

[Stefan Kottwitz]

Hi Kent,

sure, you can make an intersection of the paths, give them a name before.

If you like, post your example with the ellipse, and we will see how to exactly write this intersection.

Stefan

[kent]

Code: Select all

%Say I have the below circle node c1 definition 
\coordinate (O) at (0,0);  
\coordinate (A) at (2.0,2.0);  
\coordinate [label=left:$B$] (B) at (-2.0,2.0);  
\coordinate [label=above:$S$] (S) at (2.0,3.0);  
\node (c1) [draw,red,thick,circle through=(B)] at (S) {};
%and the following ellipse definition
\draw[green,thin,] (A) ellipse (5.0cm and 2.0cm);
%how do I create a node c2 for the ellipse such that I can use
\coordinate (X) at (intersection 2 of c1 and c2);
%to get one of the intersections between the circle and the ellipse?

[kent]

I have tried several ways to define the (c2) ellipse node, but I can't make it work.
Anybody help?

[Stefan Kottwitz]

Here is an example of intersections of a circle and an ellipse.

Code: Select all

\documentclass[margin=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{intersections}
\begin{document}
\begin{tikzpicture}
\coordinate (O) at (0,0); 
\coordinate (A) at (2.0,2.0); 
\draw [name path = c1, red,  thick] (A) circle [radius = 4cm];
\draw [name path = c2, green, thin] (A) ellipse (5.0cm and 2.0cm);
\draw [name intersections = {of = c1 and c2}]
  (intersection-1) -- (intersection-2) -- (intersection-3)
                   -- (intersection-4) -- cycle;
\end{tikzpicture}
\end{document}

intersection.png (10.11 KiB) Viewed 3520 times

Stefan

[kent]

Thanks!
Very nice indeed. This is PGF version 3?
I see that I need to install the latest PGF version. Mine is too old for the stuff I like to do.
Kent

[Stefan Kottwitz]

Yes, I use PFG/TikZ version 3. It has been released already more than 3 years ago, so time to update. See news post with features: TikZ and PGF 3.0 released on CTAN.

Stefan