c++ - 从 DXF 文件中解析不完整的椭圆

Question

我正在使用 dxflib 库开发 DXF 解析器。我在解析省略号时遇到问题。

当我解析一个椭圆时，我收到以下数据:

struct DL_EllipseData 
{
    /*! X Coordinate of center point. */
    double cx;
    /*! Y Coordinate of center point. */
    double cy;

    /*! X coordinate of the endpoint of the major axis. */
    double mx;
    /*! Y coordinate of the endpoint of the major axis. */
    double my;

    /*! Ratio of minor axis to major axis. */
    double ratio;
    /*! Startangle of ellipse in rad. */
    double angle1;
    /*! Endangle of ellipse in rad. */
    double angle2;
};

问题是，当 angle1 != 0 AND angle2 != 2* Math.PI 椭圆打开时，我无法计算表示该几何的弧路径。

例如考虑以下椭圆:

这些是它的属性:

如您所见，角度是:

angle1 = 0.81855 // 46 degrees
angle2 = 2.38934 // 136 degrees

但是椭圆的图片(我从autocad上截的，角度好像很不一样)。

在代表椭圆的 DXF 文件部分之后:

0
ELLIPSE
  5
A7
330
1F
100
AcDbEntity
  8
DL-Wall
 48
25.0
370
    -3
100
AcDbEllipse
 10
906.6576677029225
 20
906.657675539829
 30
0.0
 11
-641.4561777354752
 21
641.4561777354752
 31
0.0
210
0.0
220
0.0
230
1.0
 40
0.9999999999999978
 41
0.8185500151218715
 42
2.389346341916759

我必须如何计算正确的角度(以及弧段的起点终点)？

Answer 1

    /// <summary>
    ///     Static method to detemine the WPF end point of the arc.
    /// </summary>
    /// <param name="arc">The DXF ArcEntity object to evaluate</param>
    /// <returns>Point with values of the arc end point.</returns>
    public static Point calcEndPoint(Arc arc)
    {
        double x = (Math.Cos(arc.endAngle * (Math.PI / 180)) * arc.radius) + arc.center.X;
        double y = arc.center.Y - (Math.Sin(arc.endAngle * (Math.PI / 180)) * arc.radius);
        return new Point(x, y);
    }

    /// <summary>
    ///     Static method to detemine the WPF start point of the arc.
    /// </summary>
    /// <param name="arc">The DXF ArcEntity object to evaluate</param>
    /// <returns>Point with values of the arc start point.</returns>
    public static Point calcStartPoint(Arc arc)
    {
        double x = (Math.Cos(arc.startAngle * (Math.PI / 180)) * arc.radius) + arc.center.X;
        double y = arc.center.Y - (Math.Sin(arc.startAngle * (Math.PI / 180)) * arc.radius);
        return new Point(x, y);
    }

    public static bool checkArcSize(Arc arc)
    {
        double angleDiff = arc.endAngle - arc.startAngle;
        return !((angleDiff > 0 && angleDiff <= 180) || angleDiff <= -180);
    }

使用 System.Windows.Media.Path、PathFigure、ArcSegment:

PathFigure figure = new PathFigure();
figure.StartPoint = calcStartPoint([your arc struct]);
ArcSegment arc = new ArcSegment();
arc.Point = calcEndPoints([your arc struct]);
arc.RotationAngle = Math.Abs(endAngle - startAngle);
arc.Size = new Size(radius, radius);
arc.IsLargeArc = checkArcSize([your arc struct]);
figure.Segments.Add(arc);

您需要调整每个辅助函数以使用您的结构以及任何 C++ 与 C# 语法差异。

我相信这些辅助函数将弥合 DXF 规范为您提供的内容与在 WPF 中绘制圆弧所需内容之间的差距。