def test04_wkbwriter(self):
        wkb_w = WKBWriter()

        # Representations of 'POINT (5 23)' in hex -- one normal and
        # the other with the byte order changed.
        g = GEOSGeometry('POINT (5 23)')
        hex1 = '010100000000000000000014400000000000003740'
        wkb1 = buffer(binascii.a2b_hex(hex1))
        hex2 = '000000000140140000000000004037000000000000'
        wkb2 = buffer(binascii.a2b_hex(hex2))

        self.assertEqual(hex1, wkb_w.write_hex(g))
        self.assertEqual(wkb1, wkb_w.write(g))

        # Ensuring bad byteorders are not accepted.
        for bad_byteorder in (-1, 2, 523, 'foo', None):
            # Equivalent of `wkb_w.byteorder = bad_byteorder`
            self.assertRaises(ValueError, wkb_w._set_byteorder, bad_byteorder)

        # Setting the byteorder to 0 (for Big Endian)
        wkb_w.byteorder = 0
        self.assertEqual(hex2, wkb_w.write_hex(g))
        self.assertEqual(wkb2, wkb_w.write(g))

        # Back to Little Endian
        wkb_w.byteorder = 1

        # Now, trying out the 3D and SRID flags.
        g = GEOSGeometry('POINT (5 23 17)')
        g.srid = 4326

        hex3d = '0101000080000000000000144000000000000037400000000000003140'
        wkb3d = buffer(binascii.a2b_hex(hex3d))
        hex3d_srid = '01010000A0E6100000000000000000144000000000000037400000000000003140'
        wkb3d_srid = buffer(binascii.a2b_hex(hex3d_srid))

        # Ensuring bad output dimensions are not accepted
        for bad_outdim in (-1, 0, 1, 4, 423, 'foo', None):
            # Equivalent of `wkb_w.outdim = bad_outdim`
            self.assertRaises(ValueError, wkb_w._set_outdim, bad_outdim)

        # These tests will fail on 3.0.0 because of a bug that was fixed in 3.1:
        # http://trac.osgeo.org/geos/ticket/216
        if not geos_version_info()['version'].startswith('3.0.'):
            # Now setting the output dimensions to be 3
            wkb_w.outdim = 3

            self.assertEqual(hex3d, wkb_w.write_hex(g))
            self.assertEqual(wkb3d, wkb_w.write(g))

            # Telling the WKBWriter to inlcude the srid in the representation.
            wkb_w.srid = True
            self.assertEqual(hex3d_srid, wkb_w.write_hex(g))
            self.assertEqual(wkb3d_srid, wkb_w.write(g))
    def clean(self, value):
        """
        Validates that the input value can be converted to a Geometry
        object (which is returned).  A ValidationError is raised if
        the value cannot be instantiated as a Geometry.
        """
        if not value:
            if self.null and not self.required:
                # The geometry column allows NULL and is not required.
                return None
            else:
                raise forms.ValidationError(self.error_messages['no_geom'])

        # Trying to create a Geometry object from the form value.
        try:
            geom = GEOSGeometry(value)
        except:
            raise forms.ValidationError(self.error_messages['invalid_geom'])

        # Ensuring that the geometry is of the correct type (indicated
        # using the OGC string label).
        if str(geom.geom_type).upper(
        ) != self.geom_type and not self.geom_type == 'GEOMETRY':
            raise forms.ValidationError(
                self.error_messages['invalid_geom_type'])

        # Transforming the geometry if the SRID was set.
        if self.srid:
            if not geom.srid:
                # Should match that of the field if not given.
                geom.srid = self.srid
            elif self.srid != -1 and self.srid != geom.srid:
                try:
                    geom.transform(self.srid)
                except:
                    raise forms.ValidationError(
                        self.error_messages['transform_error'])

        return geom