return (lat,lon) for a pixel in an area image

def coord_from_area(self, x, y, lat, lon, width, ground_width):
		'''return (lat,lon) for a pixel in an area image'''

		pixel_width = ground_width / float(width)
		dx = x * pixel_width
		dy = y * pixel_width

		return mp_util.gps_offset(lat, lon, dx, -dy)