public void ArcUpdate()
        {
            // 線の太さ
            double thick = this.ViewModel.StrokeThickness;

            // 入力値切捨て
            double inputValue = Math.Floor(this.ViewModel.Percentage * 100.0);

            // 角度の計算
            double angle = (inputValue * 3.6);

            if(angle < 0)
            {
                angle += 360;
            }
            if(angle > 360)
            {
                angle %= 360.0;
            }
            // 0-360を許容
            if (0 < angle && angle < 360)
            {
                // 角度によってフラグを変える
                this.ViewModel.IsLargeArcFlg = false;
                if (angle >= 180)
                {
                    // 180°を超える(180を含む)場合はフラグをtrue
                    this.ViewModel.IsLargeArcFlg = true;
                }
            }

            // 角度と半径から座標を計算
            double radius = (this.pathArc.Width / 2) - thick;

            pathArc.StrokeThickness = thick;
            pathCircleBackground.StrokeThickness = thick;

            if (angle != 0 && angle != 360)
            {

                angle -= 90;

                double radian = Math.PI * angle / 180.0;
                double x = radius * Math.Cos(radian);
                double y = radius * Math.Sin(radian);
                x = ToRoundDown(x, 3);
                y = ToRoundDown(y, 3);

                // 終点計算
                double endPointX = radius + x + thick;
                double endPointY = radius + y + thick;

                // 図形生成
                PathFigure pfArc = new PathFigure();
                pfArc.StartPoint = new Point(100, thick); // 開始点

                // セグメント生成
                ArcSegment arc = new ArcSegment();
                arc.Point = new Point(endPointX, endPointY); // 終点(計算値)
                arc.Size = new Size(radius, radius); // 半径
                arc.IsLargeArc = this.ViewModel.IsLargeArcFlg;
                arc.SweepDirection = SweepDirection.Clockwise;
                //arc.RotationAngle = Math.PI * -90.0 / 180.0;

                // 図形入れ替え
                pfArc.Segments.Clear();
                pfArc.Segments.Add(arc);

                this.pathGeometryArc.Figures.Clear();
                this.pathGeometryArc.Figures.Add(pfArc);

                // 図形生成(背景)
                PathFigure pfCircle = new PathFigure();
                pfCircle.StartPoint = new Point(100, thick); // 開始点

                // セグメント生成
                ArcSegment circle = new ArcSegment();
                circle.Point = new Point(endPointX, endPointY); // 終点(計算値)
                circle.Size = new Size(radius, radius); // 半径
                circle.IsLargeArc = !this.ViewModel.IsLargeArcFlg;
                circle.SweepDirection = SweepDirection.Counterclockwise;

                // 図形入れ替え
                pfCircle.Segments.Clear();
                pfCircle.Segments.Add(circle);

                this.pathGeometryCircle.Figures.Clear();
                this.pathGeometryCircle.Figures.Add(pfCircle);
            }
            else
            {
                var center = new Point(this.pathArc.Width / 2, this.pathArc.Height / 2);
                var circle = new EllipseGeometry(center, radius, radius);
                var pathgeo = circle.GetOutlinedPathGeometry();

                this.pathGeometryArc.Clear();
                this.pathGeometryCircle.Clear();
                if (angle == 0)
                    this.pathGeometryCircle.Figures = pathgeo.Figures;
                else
                    this.pathGeometryArc.Figures = pathgeo.Figures;
            }
        }
 private Point GetPosition(double value, EllipseGeometry geometry)
 {
     var pathGeometry = geometry.GetOutlinedPathGeometry();
     if (pathGeometry.Figures.Count == 0)
         return geometry.Center;
     var outherGeometry = new PathGeometry(new[] { pathGeometry.Figures[0] });
     Point outherPoint, outherTangent;
     outherGeometry.GetPointAtFractionLength(value, out outherPoint, out outherTangent);
     return outherPoint;
 }