DbGeography 如何检查一个点是否在多边形内？

Question

我正在尝试在没有任何 SQL 数据库的情况下使用 DbGeography。 我有 1 个多边形 DbGeography 和 1 个点 DbGeography。

我尝试使用 polygon.Intersects(point) 来检查点是否在多边形内，但 Intersects 总是返回 true。

如何检查一个点是否在多边形内？

谢谢

编辑：

这里是多边形

POLYGON((103.000833333333 14.2038888888889,103.000833333333 17.9880555555556,103.0675 18.1216666666667,103.300833333333 18.4216666666667,103.4175 18.4383333333333,103.9675 18.3216666666667,104.334444444444 17.8213888888889,104.784444444444 17.4047222222222,104.767777777778 16.6877777777778,105.001388888889 16.2544444444444,105.418055555556 16.0044444444444,105.634722222222 15.6708333333333,105.584722222222 15.0041666666667,105.534722222222 14.5538888888889,105.068055555556 14.2205555555556,104.467777777778 14.3538888888889,103.9175 14.3372222222222,103.3675 14.3538888888889,103.000833333333 14.2038888888889))

这是重点

POINT (98.9505555555556 18.7505555555556)

Answer 1

public void CheckInPolygon()
{
    bool inPolygon;

    PointF[] pts = new PointF[] { new PointF { X = 14.2038888888889f, Y = 103.000833333333f }, 
                                    new PointF { X = 17.9880555555556f, Y = 103.000833333333f }, 
                                    new PointF { X = 18.1216666666667f, Y = 103.0675f }, 
                                    new PointF { X = 18.4216666666667f, Y = 103.300833333333f } , 
                                    new PointF { X = 18.4383333333333f, Y = 103.4175f } , 
                                    new PointF { X = 18.3216666666667f, Y = 103.9675f } , 
                                    new PointF { X = 17.8213888888889f, Y = 104.334444444444f } , 
                                    new PointF { X = 17.4047222222222f, Y = 104.784444444444f } , 
                                    new PointF { X = 16.6877777777778f, Y = 104.767777777778f } , 
                                    new PointF { X = 16.2544444444444f, Y = 105.001388888889f } , 
                                    new PointF { X = 16.0044444444444f, Y = 105.418055555556f } , 
                                    new PointF { X = 15.6708333333333f, Y = 105.634722222222f } , 
                                    new PointF { X = 15.0041666666667f, Y = 105.584722222222f } , 
                                    new PointF { X = 14.5538888888889f, Y = 105.534722222222f }, 
                                    new PointF { X = 14.2205555555556f, Y = 105.068055555556f }, 
                                    new PointF { X = 14.3538888888889f, Y = 104.467777777778f }, 
                                    new PointF { X = 14.3372222222222f, Y = 103.9175f }, 
                                    new PointF { X = 14.3538888888889f, Y = 103.3675f }, 
                                    new PointF { X = 14.2038888888889f, Y = 103.000833333333f } };      //POLYGON as provided

    inPolygon = IsInPolygon(pts, new PointF { X = 18.7505555555556f, Y = 98.9505555555556f });          //POINT as provided

    MessageBox.Show(inPolygon.ToString());      //return : false
}

public static bool IsInPolygon(PointF[] poly, PointF point)
{
    var coef = poly.Skip(1).Select((p, i) =>
                                    (point.Y - poly[i].Y) * (p.X - poly[i].X)
                                  - (point.X - poly[i].X) * (p.Y - poly[i].Y))
                                .ToList();
    if (coef.Any(p => p == 0))
        return true;

    for (int i = 1; i < coef.Count(); i++)
    {
        if (coef[i] * coef[i - 1] < 0)
            return false;
    }
    return true;
}