Hello!

Using the definition for en ellipse (http://en.wikipedia.org/wiki/Ellipse) I
can draw an arc of points. However, the end points of this arc do not
coincide with the end points of an arc drawn with the DrawArc method, e.g.

public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}

private void Form2_Paint(object sender, PaintEventArgs e)
{
Draw(e.ClipRectangle, e.Graphics);
}

private void RectCenter(Rectangle r, out int x, out int y)
{
x = (r.Left + r.Right) / 2;
y = (r.Top + r.Bottom) / 2;
}

private PointF PointFromEllipse(Rectangle bounds, float degrees)
{
float a = bounds.Width / 2.0f;
float b = bounds.Height / 2.0f;
float rad = ((float)Math.PI / 180.0f) * degrees;

int xCenter, yCenter;
RectCenter(bounds, out xCenter, out yCenter);

float x = xCenter + (a * (float)Math.Cos(rad));
float y = yCenter + (b * (float)Math.Sin(rad));

return new PointF(x, y);
}

private void Draw(Rectangle rect, Graphics g)
{

rect.Inflate(-5, -5);
g.DrawArc(new Pen(Color.Green), rect, 0, 315);
PointF p;

for (int i = 0; i < 315; i++)
{
p = PointFromEllipse(rect, i);
g.DrawLine(new Pen(Color.Red), p, new PointF(p.X, p.Y + 2));
}
}
}

Can anybody please give me an explanation for this difference?

--
Thank you,

Christopher Ireland