return pixel coordinates in the map image for a (lat,lon)
        if reverse is set, then return lat/lon for a pixel coordinate

def pixel_coords(self, latlon, reverse=False):
        '''return pixel coordinates in the map image for a (lat,lon)
        if reverse is set, then return lat/lon for a pixel coordinate
        '''
        state = self.state
        if reverse:
            (x,y) = latlon
            return self.coordinates(x,y)
        (lat,lon) = (latlon[0], latlon[1])
        return state.mt.coord_to_pixel(state.lat, state.lon, state.width, state.ground_width, lat, lon)