How to use the pyscroll.orthographic function in pyscroll

def __init__(self, filename):

        # load data from pytmx
        tmx_data = load_pygame(filename)

        # create new data source
        map_data = pyscroll.data.TiledMapData(tmx_data)

        # create new renderer
        self.map_layer = pyscroll.orthographic.BufferedRenderer(map_data, screen.get_size())

        # create a font and pre-render some text to be displayed over the map
        f = pygame.font.Font(pygame.font.get_default_font(), 20)
        t = ["scroll demo. press escape to quit",
             "arrow keys move"]

        # save the rendered text
        self.text_overlay = [f.render(i, 1, (180, 180, 0)) for i in t]

        # set our initial viewpoint in the center of the map
        self.center = [self.map_layer.map_rect.width / 2,
                       self.map_layer.map_rect.height / 2]

        # the camera vector is used to handle camera movement
        self.camera_acc = [0, 0, 0]
        self.camera_vel = [0, 0, 0]