private static void drawContour(IList <PointF> controlPoints, Image <Bgr, byte> image)
        {
            const float CONTOUR_TENSION = 0;

            /********************  contour and control points *********************/
            var pointIndices = CardinalSpline.GetEqualyDistributedPoints(controlPoints, CONTOUR_TENSION, 500);
            var points       = CardinalSpline.InterpolateAt(controlPoints, CONTOUR_TENSION, pointIndices);

            var normals       = new List <LineSegment2DF>();
            var normalIndices = CardinalSpline.GetEqualyDistributedPoints(controlPoints, CONTOUR_TENSION, 100);

            foreach (var idx in normalIndices)
            {
                var pt = CardinalSpline.InterpolateAt(controlPoints, CONTOUR_TENSION, idx);
                var normalDirection = CardinalSpline.NormalAt(controlPoints, CONTOUR_TENSION, idx);
                var orientation     = (int)Angle.ToDegrees(System.Math.Atan2(normalDirection.Y, normalDirection.X));
                var normal          = getLine(orientation, pt, 20);
                normals.Add(normal);
            }
            /********************  contour and control points *********************/

            image.Draw(points.ToArray(),
                       Bgr8.Blue,
                       3);

            image.Draw(controlPoints.Select(x => new CircleF(x, 3)), Bgr8.Red, 3);

            image.Draw(normals, Bgr8.Green, 3, false);
        }