determine if a point is an an ellipse

[illusion.admins]

I am trying to code something to tell me if a selected point is in a
particular ellipse. For the ellipse I know how it was constructed
(know the x,y, and width, height). But if I just check to see if the
point is in the rectangle making up the ellipse wouldn't that possibly
give me a false answer? Eg if the point is the upper left coordinate
of the rectangle...this point is in the rectangle making up ellipse
but NOT the ellipse itself.

Thanks for and advice.

[Peter Duniho]

On Wed, 20 Feb 2008 12:47:07 -0800, <il*************@gmail.comwrote:

In the instance of what I am using the ellipse is actually a circle.

Well, then the math is trivial. Even if you're using a square to define
the circle, the center is just the average of the top left and bottom
right corner point coordinates, the radius is half the width of the
square, and a point is inside the circle if the distance from the center
to the point is less than the radius.

Pete

[Paul E Collins]

<il*************@gmail.comwrote:

[find point inside a circle]

This is really a maths question, not a programming question, but I have
the C# code kicking around from a simple shape-based drawing application
a couple of years ago. It's for circles only, not ellipses.

public bool ContainsPoint(Point centre, int radius, Point toTest)
{
// Is the point inside the circle? Sum the squares of the
x-difference and
// y-difference from the centre, square-root it, and compare with the
radius.
// (This is Pythagoras' theorem.)

int dX = Math.Abs(toTest.X - centre.X);
int dY = Math.Abs(toTest.Y - centre.Y);

int sumOfSquares = dX * dX + dY * dY;

int distance = (int) Math.Sqrt(sumOfSquares);

return (radius >= distance);
}

Eq.

[illusion.admins]

On Feb 20, 3:59 pm, "Paul E Collins" <[e-mail]>
wrote:

<[e-mail]:

[find point inside a circle]

This is really a maths question, not a programming question, but I have
the C# code kicking around from a simple shape-based drawing application
a couple of years ago. It's for circles only, not ellipses.

public bool ContainsPoint(Point centre, int radius, Point toTest)
{
// Is the point inside the circle? Sum the squares of the
x-difference and
// y-difference from the centre, square-root it, and compare with the
radius.
// (This is Pythagoras' theorem.)

int dX = Math.Abs(toTest.X - centre.X);
int dY = Math.Abs(toTest.Y - centre.Y);

int sumOfSquares = dX * dX + dY * dY;

int distance = (int) Math.Sqrt(sumOfSquares);

return (radius >= distance);

}

Eq.

Thanks!!