如何在 VB.Net 中使用 GMap 创建圆圈

Question

我正在寻找可以在地图上创建圆圈的功能。我在 VB.Net 中使用 Gmap 库。是否存在一些可以在地图上的点周围创建一个圆的函数，例如半径为 500 米？

我找到了代码，但这不是我要找的代码：

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports GMap.NET
Imports GMap.NET.WindowsForms

Namespace Map

    Public Class GMapMarkerCircle
        Inherits GMapMarker
        Private m_Radius As Integer
        'In Meters
        Public m_OutlinePen As Pen
        Public m_FillBrush As Brush
        Public m_Fill As Boolean

        Public Sub New(p As PointLatLng, Radius As Integer, OutlinePen As Pen, FillBrush As Brush, Fill As Boolean)
            MyBase.New(p)
            m_OutlinePen = OutlinePen
            m_FillBrush = FillBrush
            m_Radius = Radius
            m_Fill = Fill
        End Sub

        Public Overrides Sub OnRender(g As Graphics)
            g.SmoothingMode = SmoothingMode.AntiAlias

            Dim R As Integer = CInt((m_Radius) / Overlay.Control.MapProvider.Projection.GetGroundResolution(Overlay.Control.Zoom, Position.Lat)) * 2

            If m_Fill = True Then
                g.FillEllipse(m_FillBrush, New System.Drawing.Rectangle(LocalPosition.X - R \ 2, LocalPosition.Y - R \ 2, R, R))
            End If
            g.DrawEllipse(m_OutlinePen, New System.Drawing.Rectangle(LocalPosition.X - R \ 2, LocalPosition.Y - R \ 2, R, R))
        End Sub

    End Class
End Namespace

在应用中：

Dim CircleMarker As New GMapMarkerCircle(New GMap.NET.PointLatLng(ZemSirka, ZemDlzka), 660, New Pen(Color.Azure, 1), Brushes.LightSeaGreen, True)
            Dim Overlay As New GMapOverlay("Circle")
            Overlay.Markers.Add(CircleMarker)
            GMapControl1.Overlays.Add(Overlay)

但是当我缩放时 in/out 地图圆圈消失了。我有一个初学者的问题：有没有可能做半透明的画笔？

Answer 1

最后，我创建了适用于短距离的代码，例如：200,300,500 米。

Public Function toRad(ByVal deegres As Double)
        Return deegres * (Math.PI / 180)
    End Function

    Public Function toDeg(ByVal radians As Double)
        Return radians * (180 / Math.PI)
    End Function

    Private Function pivotRadius(ByVal Dlzka As Double, ByVal Sirka As Double, ByVal dist As Double)

        Dim distance = (dist / earthRadius) / 1000
        Dim lat As Double = toRad(Sirka)
        Dim lng As Double = toRad(Dlzka)

        Dim points As IList(Of PointLatLng) = New List(Of PointLatLng)()

        Dim x As Integer = 0
        While x < 360
            Dim brng As Double = toRad(x)
            Dim latRadians As Double = Math.Asin(Math.Sin(lat) * Math.Cos(distance) + Math.Cos(lat) * Math.Sin(distance) * Math.Cos(brng))
            Dim lngRadians As Double = lng + (Math.Atan2(Math.Sin(brng) * Math.Sin(distance) * Math.Cos(lat), Math.Cos(distance) - Math.Sin(lat) * Math.Sin(latRadians)) / 1.6)
            points.Add(New PointLatLng(toDeg(lngRadians), toDeg(latRadians)))
            latRadians = 0
            lngRadians = 0
            x += 10
        End While

        Dim polyOverlay As New GMapOverlay("polygons")
        Dim polygon As New GMapPolygon(points, "mypolygon")
        polygon.Fill = New SolidBrush(Color.FromArgb(30, Color.Aqua))
        polygon.Stroke = New Pen(Color.Blue, 1)
        GMapControl1.Overlays.Clear()
        GMapControl1.Overlays.Add(polyOverlay)
        polyOverlay.Polygons.Add(polygon)

        Return 0

    End Function

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