private Rectangle2D GetNowViewBounds()
{
if (gMapControl1.ViewArea == null)
{
return null;
}
Point2D lefttop = Helper.PointLatLng2Point2D(gMapControl1.ViewArea.LocationTopLeft);
Point2D rightBottom = Helper.PointLatLng2Point2D(gMapControl1.ViewArea.LocationRightBottom);
Rectangle2D rec = new Rectangle2D(lefttop, rightBottom);
return rec;
}