How to use the geoalchemy2.elements.RasterElement function in GeoAlchemy2

def test_function_call(self):
        e = RasterElement(self.rast_data)
        f = e.ST_Height()
        eq_sql(f, 'ST_Height(raster(:raster_1))')
        assert f.compile().params == {u'raster_1': self.hex_rast_data}

def test_desc(self):
        e = RasterElement(self.rast_data)
        assert e.desc == self.hex_rast_data
        assert e.srid == 4326
        e = RasterElement(self.hex_rast_data)
        assert e.desc == self.hex_rast_data
        assert e.srid == 4326

def test_Raster(self):
        polygon = WKTElement('POLYGON((0 0,1 1,0 1,0 0))', srid=4326)
        o = Ocean(polygon.ST_AsRaster(5, 5))
        session.add(o)
        session.flush()
        session.expire(o)

        assert isinstance(o.rast, RasterElement)

        rast_data = (
            '01000001009A9999999999C93F9A9999999999C9BF0000000000000000000000000000F03'
            'F00000000000000000000000000000000E610000005000500440001010101010101010100'
            '010101000001010000000100000000'
        )

        assert o.rast.data == rast_data

        assert session.execute(
            select([Ocean.rast.ST_Height(), Ocean.rast.ST_Width()])
        ).fetchall() == [(5, 5)]

        # Set rast to None
        o.rast = None

select([Ocean.rast.ST_Height(), Ocean.rast.ST_Width()])
        ).fetchall() == [(5, 5)]

        # Set rast to None
        o.rast = None

        # Insert in DB
        session.flush()
        session.expire(o)

        # Check what was updated in DB
        assert o.rast is None
        assert session.execute(select([Ocean])).fetchall() == [(1, None)]

        # Reset rast to initial value
        o.rast = RasterElement(rast_data)

        # Insert in DB
        session.flush()
        session.expire(o)

        # Check what was updated in DB
        assert o.rast.data == rast_data

        assert session.execute(
            select([Ocean.rast.ST_Height(), Ocean.rast.ST_Width()])
        ).fetchall() == [(5, 5)]

def test_pickle_unpickle(self):
        import pickle
        e = RasterElement(self.rast_data)
        assert e.srid == 4326
        assert e.extended is True
        assert e.data == self.hex_rast_data
        pickled = pickle.dumps(e)
        unpickled = pickle.loads(pickled)
        assert unpickled.srid == 4326
        assert unpickled.extended is True
        assert unpickled.data == self.hex_rast_data
        f = unpickled.ST_Height()
        eq_sql(f, 'ST_Height(raster(:raster_1))')
        assert f.compile().params == {
            u'raster_1': self.hex_rast_data,
        }

def test_desc(self):
        e = RasterElement(self.rast_data)
        assert e.desc == self.hex_rast_data
        assert e.srid == 4326
        e = RasterElement(self.hex_rast_data)
        assert e.desc == self.hex_rast_data
        assert e.srid == 4326

elif isinstance(bindvalue, WKBElement):
                if dialect.name == 'sqlite' or not bindvalue.extended:
                    # With SpatiaLite or when the WKBElement includes a WKB value rather
                    # than a EWKB value we use Shapely to convert the WKBElement to an
                    # EWKT string
                    if not SHAPELY:
                        raise ArgumentError('Shapely is required for handling WKBElement bind '
                                            'values when using SpatiaLite or when the bind value '
                                            'is a WKB rather than an EWKB')
                    shape = to_shape(bindvalue)
                    return 'SRID=%d;%s' % (bindvalue.srid, shape.wkt)
                else:
                    # PostGIS ST_GeomFromEWKT works with EWKT strings as well
                    # as EWKB hex strings
                    return bindvalue.desc
            elif isinstance(bindvalue, RasterElement):
                return '%s' % (bindvalue.data)
            else:
                return bindvalue
        return process