int maxPixelInCurrentZoomLevel = (int)Math.Pow(2, zoomLevel) * 256 - 1;

            PointShape ddCenter = canvas.CurrentWorldExtent.GetCenterPoint();
            PointShape projectedCenter = projection.ConvertToExternalProjection(ddCenter) as PointShape;
            RectangleShape maxExtentInMeter = BingMapsTileSystem.GetMaxExtentInMeter(projection);
            if (ddCenter.X < maxExtentInMeter.UpperLeftPoint.X)
            {
                projectedCenter.X -= 360;
            }
            if (ddCenter.X > maxExtentInMeter.LowerRightPoint.X)
            {
                projectedCenter.X += 360;
            }

            BingMapsTileSystem.LatLongToPixelXY(projectedCenter.Y, projectedCenter.X, zoomLevel, out pixelCenterX, out pixelCenterY);

            int minX = (int)Math.Ceiling(pixelCenterX - canvas.Width * 0.5);
            int minY = (int)Math.Ceiling(pixelCenterY - canvas.Height * 0.5);
            int maxX = (int)Math.Floor(pixelCenterX + canvas.Width * 0.5);
            int maxY = (int)Math.Floor(pixelCenterY + canvas.Height * 0.5);
            if (minX < 0)
            {
                minX = 0;
            }
            if (minY < 0)
            {
                minY = 0;
            }
            if (maxX > maxPixelInCurrentZoomLevel)
            {
                maxX = maxPixelInCurrentZoomLevel;
            }
            if (maxY > maxPixelInCurrentZoomLevel)
            {
                maxY = maxPixelInCurrentZoomLevel;
            }

            int startTileColumn = (int)Math.Floor(minX / (double)TileWidth);
            int endTileColumn = (int)Math.Ceiling(maxX / (double)TileWidth);
            int startTileRow = (int)Math.Floor(minY / (double)TileHeight);
            int endTileRow = (int)Math.Ceiling(maxY / (double)TileHeight);


public static void LatLongToPixelXY(double latitude, double longitude, int levelOfDetail, out int pixelX, out int pixelY)
        {
            double sinLatitude = Math.Sin(latitude * Math.PI / 180);
            double x = (longitude + 180) / 360;
            double y = 0.5 - Math.Log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);

            uint mapSize = MapSize(levelOfDetail);
            pixelX = (int)(x * mapSize + 0.5);
            pixelY = (int)(y * mapSize + 0.5);
        }