>>I think I've done this in the past by creating a region (say a rectangular one based on your four points) then using the .Union() method against each object of interest. If the result is null then the object is not within the region. (This can also be used for selecting muliple objects). It's possible that none of your four points will actually fall within the ellipse even though the initial point is very close to it..
>>Haven't access to .NET at the moment so I can't test it.....
>>Best,
>>Viv
>
>
>I like this idea. Could be helpful as I continue to work with shapes on a canvas.

Actually using Geometries rather than regions might be better. This works:

        private void Canvas_MouseDown(object sender, MouseButtonEventArgs e)
        {
            //Circle around clicked point:
            double tolerance = 4;
            Point ClickedPoint = e.GetPosition(MainCanvas);
            EllipseGeometry eg = new EllipseGeometry();
            eg.RadiusX = tolerance; eg.RadiusY = tolerance;
            eg.Center = ClickedPoint;

            // Geometry of an ellipse object on the canvas:
            EllipseGeometry eg2 = new EllipseGeometry();

            foreach (Ellipse TargetEllipse in MainCanvas.Children)
            {
                eg2.RadiusX = TargetEllipse.Width / 2;
                eg2.RadiusY = TargetEllipse.Height / 2;
                eg2.Center = new Point(
                    ((double)TargetEllipse.GetValue(Canvas.LeftProperty)) + TargetEllipse.Width / 2,
                    ((double)TargetEllipse.GetValue(Canvas.TopProperty)) + TargetEllipse.Height / 2
                    );

                //Combine them
                CombinedGeometry cg = new CombinedGeometry(GeometryCombineMode.Intersect, eg, eg2);

                //Is there an overlap
                if (!cg.Bounds.IsEmpty)
                {
                    // Close enough - do something
                }
            }
        }

Rough code to work with ellipses only - better code would cope with any shape on the Canvas....
Best,
Viv