Checking if a x,y position is within a dynamically generated Ellipse

Question

I'm trying to calculate whether or not a specific X,Y position lies within an ellipse in C#.

The available variables to work with are: X (the X I want to check) Y (the Y I want to check) The width of the ellipse The height of the ellipse The x-center of the ellipse (as the ellipse is drawn somehwere on a screen, it has to be calculated). The y-center of the ellipse (again, random position, so this had to be calculated.

So far I tried basic mathematics, but those wouldn't get me as far as I needed.

Why basic math failed? There is ellipse equation to which you should be able to use you x and y to calculate if the point is on or inside of ellipse or outside of it. Why is that a problem? — Jarek, Apr 19 '13 at 13:42
It failed becuase of human error of course. A misscalculation in determining where the ellipse was on the screen. I feel such an idiot sometimes. — Rik_S, Apr 20 '13 at 12:07

score 1 · Answer 1 · answered Apr 19 '13 at 13:40

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Try yourEllipse.RenderedGeometry.StrokeContains(Pen pen, Point point) method

answered Apr 19 '13 at 13:40

Hossein Narimani Rad

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score 1 · Accepted Answer · answered Apr 19 '13 at 17:47

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Is the ellipse horizontal, or rotated?

For horizontal ellipse with center (xc,yc) and radii rx and ry all the points inside obey the equation

((x-xc)/rx)^2 + ((y-yc)/ry)^2 <= 1

So just check your point (x,y) against the equation above.

answered Apr 19 '13 at 17:47

John Alexiou

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I tried this equation before and it didn't work. Turned out to be a mistake on my part... Miss placement of a couple of brackets in the calculation of the position of the ellipse. – Rik_S Apr 20 '13 at 12:06
So it works now, right? – John Alexiou Apr 20 '13 at 15:30
Yes, it does work now :) – Rik_S Apr 21 '13 at 10:48

Checking if a x,y position is within a dynamically generated Ellipse

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