坐标点计算

Question

圆内正切三角形坐标点计算.
已知圆心位置(x,y),半径(r),如何計算出三角形的各個坐標點?
或者:如何根据角度计算坐标?

Answer 1

     /// <summary>
        /// 通过点坐标算得到角度
        /// </summary>
        /// <param name="xy">图边上的某点坐标</param>
        /// <param name="origin">原心坐标</param>
        /// <returns></returns>
        private float XYToDegrees(Point xy, Point origin)
        {
            double angle = 0.0;            if (xy.Y < origin.Y)
            {
                if (xy.X > origin.X)
                {
                    angle = (double)(xy.X - origin.X) / (double)(origin.Y - xy.Y);
                    angle = Math.Atan(angle);
                    angle = 90.0 - angle * 180.0 / Math.PI;
                }
                else if (xy.X < origin.X)
                {
                    angle = (double)(origin.X - xy.X) / (double)(origin.Y - xy.Y);
                    angle = Math.Atan(-angle);
                    angle = 90.0 - angle * 180.0 / Math.PI;
                }
            }
            else if (xy.Y > origin.Y)
            {
                if (xy.X > origin.X)
                {
                    angle = (double)(xy.X - origin.X) / (double)(xy.Y - origin.Y);
                    angle = Math.Atan(-angle);
                    angle = 270.0 - angle * 180.0 / Math.PI;
                }
                else if (xy.X < origin.X)
                {
                    angle = (double)(origin.X - xy.X) / (double)(xy.Y - origin.Y);
                    angle = Math.Atan(angle);
                    angle = 270.0 - angle * 180.0 / Math.PI;
                }
            }            if (angle > 180) angle -= 360; //Optional. Keeps values between -180 and 180
            return (float)angle;
        }
        
        /// <summary>
        /// 通过点坐标计算得到新的坐标
        /// </summary>
        /// <param name="center">以哪一点为坐标原点</param>
        /// <param name="point">转前的坐标</param>
        /// <param name="angleInDegree">转的角度</param>
        /// <returns></returns>
        public static Point Rotate(PointF center, PointF point, float angleInDegree)
        {
            System.Drawing.Drawing2D.Matrix matrix = new System.Drawing.Drawing2D.Matrix();
            matrix.Rotate(angleInDegree);                                                     // 构造一个逆时针旋转的矩阵            PointF[] points = { new PointF(point.X - center.X, point.Y - center.Y) };        // 把坐标原点移到'那个原点'那里
            matrix.TransformPoints(points);                                                 // 旋转
            int x = (int)(center.X + points[0].X);
            int y = (int)(center.Y + points[0].Y);
            return new Point(x, y);                                                        // 把坐标原点移回去
        }
我工程里用的，你参考一下

Answer 2

圆内正切三角形是什么东东？public Point FindPoint(double a)
{
return new Point(x+r*Math.Cos(a),y+r*Math.Sin(a));
}