判断点是否在多边形内部 -

判断点是否在多边形内部

http://bbs.mjtd.com/thread-92445-1-1.html

Public Function ptInPolygon1(pt As Point3d, pPolyline As Polyline) As Integer
    Dim count As Integer = pPolyline.NumberOfVertices
    '构建多边形外接矩形
    Dim maxx As Double = Double.MinValue, maxy As Double = Double.MinValue, minx As Double = Double.MaxValue, miny As Double = Double.MaxValue
    Dim i As Integer = 0
    While i < count
        If pPolyline.GetPoint3dAt(i).X > maxx Then
            maxx = pPolyline.GetPoint3dAt(i).X
        End If
        If pPolyline.GetPoint3dAt(i).Y > maxy Then
            maxy = pPolyline.GetPoint3dAt(i).Y
        End If
        If pPolyline.GetPoint3dAt(i).X < minx Then
            minx = pPolyline.GetPoint3dAt(i).X
        End If
        If pPolyline.GetPoint3dAt(i).Y < miny Then
            miny = pPolyline.GetPoint3dAt(i).Y
        End If
        System.Math.Max(System.Threading.Interlocked.Increment(i),i - 1)
    End While
    If pt.X > maxx OrElse pt.Y > maxy OrElse pt.X < minx OrElse pt.Y < miny Then
        Return -1
    End If

    Dim line1 As New Line(New Point3d(maxx, pt.Y, 0), New Point3d(minx, pt.Y, 0))

    Dim crossCount As Integer = 0

    Using tran As Transaction = pDatabase.TransactionManager.StartTransaction()
        Dim pBlockTableRecord As BlockTableRecord = TryCast(tran.GetObject(pDatabase.CurrentSpaceId, OpenMode.ForWrite), BlockTableRecord)

        Dim crossPoint As New Point3dCollection()

        line1.IntersectWith(pPolyline, Intersect.OnBothOperands, crossPoint, 0, 0)
        If crossPoint.Count >= 1 Then
            Dim n As Integer = 0
            While n < crossPoint.Count
                Dim crossPt As Point3d = crossPoint(n)
                If crossPt.X > pt.X Then
                    System.Math.Max(System.Threading.Interlocked.Increment(crossCount),crossCount - 1)

                    Dim pCircle As New Circle(crossPt, Vector3d.ZAxis, 2)

                    pBlockTableRecord.AppendEntity(pCircle)
                    tran.AddNewlyCreatedDBObject(pCircle, True)
                End If
                System.Math.Max(System.Threading.Interlocked.Increment(n),n - 1)

            End While
        End If
        Dim circle As New Circle(pt, Vector3d.ZAxis, 2)
        pBlockTableRecord.AppendEntity(circle)
        tran.AddNewlyCreatedDBObject(circle, True)

        pBlockTableRecord.AppendEntity(line1)
        tran.AddNewlyCreatedDBObject(line1, True)
        tran.Commit()
    End Using
    Return crossCount Mod 2

End Function

还可以参考：http://bbs.xdcad.net/thread-715959-1-1.html

判断点是否在多边形内部
如何判断一个点是否在多边形内部？

（1）面积和判别法：判断目标点与多边形的每条边组成的三角形面积和是否等于该多边形，相等则在多边形内部。

（2）夹角和判别法：判断目标点与所有边的夹角和是否为360度，为360度则在多边形内部。

（3）引射线法：从目标点出发引一条射线，看这条射线和多边形所有边的交点数目。如果有奇数个交点，则说明在内部，如果有偶数个交点，则说明在外部。

[本日志由 tiancao1001 于 2018-10-24 11:05 AM 编辑]

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