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Index › Programming Questions & Help › Programs › line across an ellipse
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line across an ellipse (Read 2595 times)
Robert
line across an ellipse
Jun 14th, 2010, 11:12am  
I found this code for making random lines across a circle, but I don't know how to alter it to make lines across an ellipse.  Any help will be appreciated.

Quote:
  float theta = random(TWO_PI);
  float sx = cos(theta)*radius;
  float sy = sin(theta)*radius;

  float delta = theta + PI + random(-anglerange,anglerange);
  float sx2 = cos(delta)*radius;
  float sy2 = sin(delta)*radius;


  Line L = new Line(new PVector(sx,sy), new PVector(sx2,sy2));
  Lines.add(L);
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Quark
Re: line across an ellipse
Reply #1 - Jun 14th, 2010, 12:42pm  
Effectively  an ellipse has 2 radii which if we call the radiusX and radiusY then you can use

Code:
  float theta = random(TWO_PI);
  float sx = cos(theta)*radiusX;
  float sy = sin(theta)*radiusY;

 float delta = theta + PI + random(-anglerange,anglerange);
  float sx2 = cos(delta)*radiusX;
  float sy2 = sin(delta)*radiusY;
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WWW  
Robert
Re: line across an ellipse
Reply #2 - Jun 14th, 2010, 1:57pm  
perfect, thank you.

I should have been able to figure that out.
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Robert
Re: line across an ellipse
Reply #3 - Jun 14th, 2010, 3:01pm  
I appreciate the help.  I'm wondering how hard it would be to so the same with a sphere.
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blindfish
Re: line across an ellipse
Reply #4 - Jun 14th, 2010, 3:27pm  
Just thinking aloud here, but any point on a sphere can be defined by two circles perpendicular to each other: i.e. set a random rotation on one axis around one circle and from that point rotate around the other axis...  though I'm sure there's a much more elegant mathematical solution.  In fact google gives plenty of results on this.  This is one for the maths geeks whilst this gives a more obvious option to implement...
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Where is the what if the what is in why?
 
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