Source code for astropy.coordinates.builtin_frames.altaz

# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
from __future__ import (absolute_import, unicode_literals, division,
                        print_function)

import numpy as np

from ... import units as u
from .. import representation as r
from ..baseframe import BaseCoordinateFrame, RepresentationMapping
from ..attributes import (Attribute, TimeAttribute,
                          QuantityAttribute, EarthLocationAttribute)

_90DEG = 90*u.deg


[docs]class AltAz(BaseCoordinateFrame): """ A coordinate or frame in the Altitude-Azimuth system (Horizontal coordinates). Azimuth is oriented East of North (i.e., N=0, E=90 degrees). This frame is assumed to *include* refraction effects if the ``pressure`` frame attribute is non-zero. The frame attributes are listed under **Other Parameters**, which are necessary for transforming from AltAz to some other system. Parameters ---------- representation : `BaseRepresentation` or None A representation object or None to have no data (or use the other keywords) az : `Angle`, optional, must be keyword The Azimuth for this object (``alt`` must also be given and ``representation`` must be None). alt : `Angle`, optional, must be keyword The Altitude for this object (``az`` must also be given and ``representation`` must be None). distance : :class:`~astropy.units.Quantity`, optional, must be keyword The Distance for this object along the line-of-sight. pm_az_cosalt : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion in azimuth (including the ``cos(alt)`` factor) for this object (``pm_alt`` must also be given). pm_alt : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion in altitude for this object (``pm_az_cosalt`` must also be given). radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword The radial velocity of this object. copy : bool, optional If `True` (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument. differential_cls : `BaseDifferential`, dict, optional A differential class or dictionary of differential classes (currently only a velocity differential with key 's' is supported). This sets the expected input differential class, thereby changing the expected keyword arguments of the data passed in. For example, passing ``differential_cls=CartesianDifferential`` will make the classes expect velocity data with the argument names ``v_x, v_y, v_z``. Other parameters ---------------- obstime : `~astropy.time.Time` The time at which the observation is taken. Used for determining the position and orientation of the Earth. location : `~astropy.coordinates.EarthLocation` The location on the Earth. This can be specified either as an `~astropy.coordinates.EarthLocation` object or as anything that can be transformed to an `~astropy.coordinates.ITRS` frame. pressure : `~astropy.units.Quantity` The atmospheric pressure as an `~astropy.units.Quantity` with pressure units. This is necessary for performing refraction corrections. Setting this to 0 (the default) will disable refraction calculations when transforming to/from this frame. temperature : `~astropy.units.Quantity` The ground-level temperature as an `~astropy.units.Quantity` in deg C. This is necessary for performing refraction corrections. relative_humidity`` : numeric The relative humidity as a number from 0 to 1. This is necessary for performing refraction corrections. obswl : `~astropy.units.Quantity` The average wavelength of observations as an `~astropy.units.Quantity` with length units. This is necessary for performing refraction corrections. Notes ----- The refraction model is based on that implemented in ERFA, which is fast but becomes inaccurate for altitudes below about 5 degrees. Near and below altitudes of 0, it can even give meaningless answers, and in this case transforming to AltAz and back to another frame can give highly discrepent results. For much better numerical stability, leaving the ``pressure`` at ``0`` (the default), disabling the refraction correction (yielding "topocentric" horizontal coordinates). """ frame_specific_representation_info = { r.SphericalRepresentation: [ RepresentationMapping('lon', 'az'), RepresentationMapping('lat', 'alt') ], r.SphericalCosLatDifferential: [ RepresentationMapping('d_lon_coslat', 'pm_az_cosalt', u.mas/u.yr), RepresentationMapping('d_lat', 'pm_alt', u.mas/u.yr), RepresentationMapping('d_distance', 'radial_velocity', u.km/u.s), ], r.SphericalDifferential: [ RepresentationMapping('d_lon', 'pm_az', u.mas/u.yr), RepresentationMapping('d_lat', 'pm_alt', u.mas/u.yr), RepresentationMapping('d_distance', 'radial_velocity', u.km/u.s) ], r.CartesianDifferential: [ RepresentationMapping('d_x', 'v_x', u.km/u.s), RepresentationMapping('d_y', 'v_y', u.km/u.s), RepresentationMapping('d_z', 'v_z', u.km/u.s), ], } frame_specific_representation_info[r.UnitSphericalRepresentation] = \ frame_specific_representation_info[r.SphericalRepresentation] frame_specific_representation_info[r.UnitSphericalCosLatDifferential] = \ frame_specific_representation_info[r.SphericalCosLatDifferential] frame_specific_representation_info[r.UnitSphericalDifferential] = \ frame_specific_representation_info[r.SphericalDifferential] default_representation = r.SphericalRepresentation default_differential = r.SphericalCosLatDifferential obstime = TimeAttribute(default=None) location = EarthLocationAttribute(default=None) pressure = QuantityAttribute(default=0, unit=u.hPa) temperature = QuantityAttribute(default=0, unit=u.deg_C) relative_humidity = Attribute(default=0) obswl = QuantityAttribute(default=1*u.micron, unit=u.micron) def __init__(self, *args, **kwargs): super(AltAz, self).__init__(*args, **kwargs) @property def secz(self): """ Secant if the zenith angle for this coordinate, a common estimate of the airmass. """ return 1/np.sin(self.alt) @property def zen(self): """ The zenith angle for this coordinate """ return _90DEG.to(self.alt.unit) - self.alt
# self-transform defined in cirs_observed_transforms.py