C# Drawing Arc with 3 Points

Question

I need to draw an arc using GraphicsPath and having initial, median and final points. The arc has to pass on them.

I tried .DrawCurve and .DrawBezier but the result

Answer 1

Have you tried the DrawArc method and seeing if u can manipulate your 3 points somehow?

maybe

Pen blackPen= new Pen(Color.Black, 3);
// Create rectangle to bound ellipse.
Rectangle rect = new Rectangle(initial x, initial y, final x, median y);
// Create start and sweep angles on ellipse.
float startAngle =  0F;
float sweepAngle = 270.0F;
// Draw arc to screen.
e.Graphics.DrawArc(blackPen, rect, startAngle, sweepAngle);

http://msdn.microsoft.com/en-us/library/system.drawing.graphics.drawarc%28VS.71%29.aspx

Answer 2

I would use DrawArc() as suggested by ANC_Michael. To find an arc that passes through 3 points you want to calculate the circumcircle of the triangle formed by the points.

Once you have the circumcircle calculate a bounding box for the circle to use with DrawArc using the min/max dimensions (center +/- radius). Now calculate your start and stop angles by translating the points so that the circumcircle is centered on the origin (translate by -circumcenter) and take the dot-product of the normalized start and end vectors with the X-axis:

double startAngle = Math.Acos(VectorToLeftPoint.Dot(XAxis));
double stopAngle = Math.Acos(VectorToRightPoint.Dot(XAxis));

Note that DrawArc expects angles clockwise from the X-axis so you should add Math.PI if the calculated vector is above the x-axis. That should be enough information to call DrawArc().

Edit: This method will find a circular arc and not necessarily the 'best fit' arc depending on your expected endpoint behavior.