gt_load_png_as_traffic_raster
                        Converts PNG to raster
gt_make_grid            Creates Grid to Query Google Traffic
gt_make_png             Make Google Traffic PNG
gt_make_raster          Make Google Traffic Raster
gt_make_raster_from_grid
                        Make Google Traffic Raster Based on Grid of
                        Coordinates
gt_make_raster_from_polygon
                        Make Google Traffic Raster Based on Polygon
gt_mosaic               Mosaic rasters with different origins and
                        resolutions
