How to use the gpxpy.gpx.GPXWaypoint function in gpxpy

'copyright:copyright_author:copyright_year:copyright_license',
                    mod_gpxfield.GPXField('copyright_author', attribute='author'),
                    mod_gpxfield.GPXField('copyright_year', tag='year'),
                    mod_gpxfield.GPXField('copyright_license', tag='license'),
                '/copyright',
                'link:@link',
                    mod_gpxfield.GPXField('link', attribute='href'),
                    mod_gpxfield.GPXField('link_text', tag='text'),
                    mod_gpxfield.GPXField('link_type', tag='type'),
                '/link',
                mod_gpxfield.GPXField('time', type=mod_gpxfield.TIME_TYPE),
                mod_gpxfield.GPXField('keywords'),
                mod_gpxfield.GPXComplexField('bounds', classs=GPXBounds),
                mod_gpxfield.GPXExtensionsField('metadata_extensions', tag='extensions'),
            '/metadata',
            mod_gpxfield.GPXComplexField('waypoints', classs=GPXWaypoint, tag='wpt', is_list=True),
            mod_gpxfield.GPXComplexField('routes', classs=GPXRoute, tag='rte', is_list=True),
            mod_gpxfield.GPXComplexField('tracks', classs=GPXTrack, tag='trk', is_list=True),
            mod_gpxfield.GPXExtensionsField('extensions', is_list=True),
    ]

    __slots__ = ('version', 'creator', 'name', 'description', 'author_name',
                 'author_email', 'link', 'link_text', 'time', 'keywords',
                 'bounds', 'waypoints', 'routes', 'tracks', 'author_link',
                 'author_link_text', 'author_link_type', 'copyright_author',
                 'copyright_year', 'copyright_license', 'link_type',
                 'metadata_extensions', 'extensions', 'nsmap',
                 'schema_locations')

    def __init__(self):
        self.version = None
        self.creator = None

def end_object(self, trek):
        super(TrekGPXSerializer, self).end_object(trek)
        for poi in trek.published_pois.all():
            geom_3d = poi.geom_3d.transform(4326, clone=True)  # GPX uses WGS84
            wpt = gpxpy.gpx.GPXWaypoint(latitude=geom_3d.y,
                                        longitude=geom_3d.x,
                                        elevation=geom_3d.z)
            wpt.name = u"%s: %s" % (poi.type, poi.name)
            wpt.description = poi.description
            self.gpx.waypoints.append(wpt)

    def _point_to_GPX(self, point, klass=gpxpy.gpx.GPXWaypoint):
        if isinstance(point, (tuple, list)):
            point = Point(*point, srid=settings.SRID)
        newpoint = point.transform(4326, clone=True)  # transformation: gps uses 4326
        # transform looses the Z parameter
        return klass(latitude=newpoint.y, longitude=newpoint.x, elevation=point.z)

    def _point_to_GPX(self, point, klass=gpxpy.gpx.GPXWaypoint):
        if isinstance(point, (tuple, list)):
            point = Point(*point, srid=settings.SRID)
        newpoint = point.transform(4326, clone=True)  # transformation: gps uses 4326
        # transform looses the Z parameter
        return klass(latitude=newpoint.y, longitude=newpoint.x, elevation=point.z)

    def _point_to_GPX(self, point, klass=gpxpy.gpx.GPXWaypoint):
        if isinstance(point, (tuple, list)):
            point = Point(*point, srid=settings.SRID)
        x, y = point.transform(4326, clone=True)  # transformation: gps uses 4326
        z = point.z  # transform looses the Z parameter
        return klass(latitude=y, longitude=x, elevation=z)