public Utf8Grid(int utfGridResolution, int tileX, int tileY, int zoom)
{
_utfGridResolution = utfGridResolution;
var size = new Size(256 / utfGridResolution, 256 / utfGridResolution);
_bitmap = new Bitmap(size.Width, size.Height,PixelFormat.Format32bppRgb);
_graphics = Graphics.FromImage(_bitmap);
var bbox = GetBoundingBoxInLatLngWithMargin(tileX, tileY, zoom);
_graphicsPathBuilder = new GraphicsPathBuilder(SphericalMercator.FromLonLat(bbox), new Size(256 / _utfGridResolution, 256 / _utfGridResolution));
this.Keys = new List<string>();
this.Data = new Dictionary<string, object>();
this.Grid = new List<string>();
}