return pixel coordinates in the map image for a (lat,lon)

def pixel_coords(latlon, ground_width=0, mt=None, topleft=None, width=None):
    '''return pixel coordinates in the map image for a (lat,lon)'''
    (lat,lon) = (latlon[0], latlon[1])
    return mt.coord_to_pixel(topleft[0], topleft[1], width, ground_width, lat, lon)