如何实现经度纬度到平面坐标的相互转换(VB.net)

投影过程（C#）：

/// flatref 投影的坐标系统，这里的54013是世界投影，世界投影所有经纬度都可以转换为平面坐标，但是由于投影面积大失真也会比较大（相当于把整个地球劈成一片片的，然后拉伸最后贴到平面上，失真当然大了）。当然也可以选择精度更高的平面如：esriSRProjCS_Beijing1954GK_23N

对应数值21483 仅仅把北京附近的地球平面拉伸铺在平面上，由于投影面积变小，所以投影经度提高。但是由于面积变小，所以有些经度纬度不能转换，比如所美国的精度纬度用北京投影就投不了。

flatref = pfactory.CreateProjectedCoordinateSystem(54013); //没什么说的，标准大地经纬度，可以将X-Y逆投影为经度和纬度

earthref = pfactory.CreateGeographicCoordinateSystem((int)esriSRGeoCSType.esriSRGeoCS_NAD1983); /// 将经纬度点转换为平面坐标。

private IPoint GetProject(double x, double y)

{

    IPoint pt = new PointClass();

    pt.PutCoords(x, y);

    IGeometry geo = (IGeometry)pt;

    geo.SpatialReference = earthref;

    geo.Project(flatref); return pt;

} /// 将平面坐标转换为经纬度。

private IPoint GetGeo(double x, double y)

{

    IPoint pt = new PointClass();

    pt.PutCoords(x, y);

    IGeometry geo = (IGeometry)pt;

    geo.SpatialReference = flatref;

    geo.Project(earthref);

    double xx = pt.X;

    return pt;

}

实际上IPoint的投影和任何地图都没什么大关系，完全可以不用地图，直接调用IPoint进行投影的转换

Private Function transformToProject(x As Double, y As Double) As IPoint

Dim pt As IPoint, geo As IGeometry

Dim pProjCoordSys As IProjectedCoordinateSystem

Dim pGCS As IGeographicCoordinateSystem

Dim pSpatRefFact As ISpatialReferenceFactory

'Set the spatial reference factory to a new spatial reference environment

Set pSpatRefFact = New SpatialReferenceEnvironment

Set pProjCoordSys = pSpatRefFact.CreateProjectedCoordinateSystem(esriSRProjCS_WGS1984UTM_47N)

Set pGCS = pSpatRefFact.CreateGeographicCoordinateSystem(esriSRGeoCSType.esriSRGeoCS_NAD1983)

Set pt = New Point

pt.PutCoords x, y

Set geo = pt

Set geo.SpatialReference = pGCS

geo.Project pProjCoordSys

Set transformToProject = pt

End Function