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# drawing ellipses

Posted on 2006-06-20
Medium Priority
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HI,
i am drawing ellipses using actionScript.
i need to know if there is a way to know the common area of two ellipses, and fill it with a color.
thanks
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Question by:mte01
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LVL 7

Expert Comment

ID: 16961235
How are you drawing them, with "curveTo"?
I just want to know what data you know about each one, so I can start to figure the math for you.

MuXx
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LVL 7

Expert Comment

ID: 16961245
And, yes. You can know the common area of them. :-) And once you know that you can change it's colour.
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LVL 3

Author Comment

ID: 16990216
HI,
I AM USING THIS LIBRARY, it contain the classes needed to draw the ellipses, every thing works fine, i just need to get the common area
http://www.mediaverk.lv/asd/
thanks for the help
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LVL 7

Accepted Solution

muxxter earned 1500 total points
ID: 17005373
Hi mte01, sorry it took me so long to get back to you.

Ok, the library you use does give all the needed information. However, the math involved in finding out if two points from different ellipses is non-trivial. If the ellipse was at the origin, the equation for find a point is:

(x^2/a^2) + (Y^2/b^2) < 1 ... where 'a' and 'b' are the semi-major and semi-minor axis respectively

If a point (X, Y) safisfy this condition, it is inside in the ellipse. However, those ellipses you speak of are probably not both at the origin. Plus, that isn't a very prety way of getting an area, you'd have to do it a whole bunch of time just to get a few points.
I would suggest trying a more math oriented forum. Try "http://mathforum.org/dr.math/", it seems pretty good.

The good news is that the library you're using has all the goodies you need to be able to calculate the needed areas:

drawX - the X coordinate of the center of the ellipse
drawY - the Y coordinate

radiusX - the width of the ellipse (this would also be called the MAJOR axis)
radiusY - the height of the ellipse (this would also be called the MINOR axis)

rotation - the angle of orientation of the ellipse (judging from the example, I'd say it's in degrees, rotating clockwise)

Using these parameters, I'm sure there's math out there that can help you out. Unfortunately, my major in University was computer science, not math. :-)

I hope this helps,
MuXx
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LVL 3

Author Comment

ID: 17009379
yeah man, thanks,
i already checked the library, pretty strong and it's easy to use, but i doubt that Dr. Math can have the time to answer me...
an idea i got it to loop on all the points in the graph, and check if this point verify the ellipse's equation... but 400pixel * 400 pixel * the number of ellipses it a lot..
anyways thanks for the help.
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