Source code for pydl.pydlutils.coord
# Licensed under a 3-clause BSD style license - see LICENSE.rst
# -*- coding: utf-8 -*-
"""This module corresponds to the coord directory in idlutils.
"""
import numpy as np
import astropy.units as u
import astropy.coordinates as ac
from ..goddard.astro import get_juldate
[docs]
class SDSSMuNu(ac.BaseCoordinateFrame):
"""SDSS Great Circle Coordinates
Attributes
----------
stripe
SDSS `Stripe Number`_ .
node
Node of the great circle with respect to the celestial equator.
In SDSS, this is almost always RA = 95.0 degrees.
incl
Inclination of the great circle with respect to the celestial
equator.
phi
Counter-clockwise position angle w.r.t. north for an arc
in the +nu direction.
Parameters
----------
mu : :class:`~astropy.coordinates.Angle`
Angle corresponding to longitude measured along a stripe.
nu : :class:`~astropy.coordinates.Angle`
Angle corresponding to latitude measured perpendicular to a stripe.
Notes
-----
https://www.sdss4.org/dr16/algorithms/surveycoords/
.. _`Stripe Number`: https://www.sdss4.org/dr16/help/glossary/#stripe
"""
default_representation = ac.SphericalRepresentation
frame_specific_representation_info = {
'spherical': [ac.RepresentationMapping(reprname='lon', framename='mu',
defaultunit=u.deg),
ac.RepresentationMapping(reprname='lat', framename='nu',
defaultunit=u.deg)]}
frame_specific_representation_info['unitspherical'] = frame_specific_representation_info['spherical']
stripe = ac.Attribute(default=0)
node = ac.QuantityAttribute(default=ac.Angle(95.0, unit=u.deg),
unit=u.deg)
# phi = ac.QuantityFrameAttribute(default=None, unit=u.deg)
@property
def incl(self):
return ac.Angle(stripe_to_incl(self.stripe), unit=u.deg)
[docs]
def current_mjd():
"""Return the current MJD.
"""
return get_juldate() - 2400000.5
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@ac.frame_transform_graph.transform(ac.FunctionTransform, SDSSMuNu, ac.ICRS)
def munu_to_radec(munu, icrs_frame):
"""Convert from SDSS great circle coordinates to equatorial coordinates.
Parameters
----------
munu : :class:`~pydl.pydlutils.coord.SDSSMuNu`
SDSS great circle coordinates (mu, nu).
Returns
-------
:class:`~astropy.coordinates.ICRS`
Equatorial coordinates (RA, Dec).
"""
# from pydlutils.coord import stripe_to_eta
# from pydlutils.goddard.misc import cirrange
# if 'stripe' in kwargs:
# node = 95.0
# incl = stripe_to_incl(kwargs['stripe'])
# elif 'node' in kwargs and 'incl' in kwargs:
# node = kwargs['node']
# incl = kwargs['incl']
# else:
# raise ValueError('Must specify either STRIPE or NODE,INCL!')
# if mu.size != nu.size:
# raise ValueError('Number of elements in MU and NU must agree!')
sinnu = np.sin(munu.nu.to(u.radian).value)
cosnu = np.cos(munu.nu.to(u.radian).value)
sini = np.sin(munu.incl.to(u.radian).value)
cosi = np.cos(munu.incl.to(u.radian).value)
sinmu = np.sin((munu.mu - munu.node).to(u.radian).value)
cosmu = np.cos((munu.mu - munu.node).to(u.radian).value)
xx = cosmu * cosnu
yy = sinmu * cosnu * cosi - sinnu * sini
zz = sinmu * cosnu * sini + sinnu * cosi
ra = ac.Angle(np.arctan2(yy, xx), unit=u.radian) + munu.node
dec = ac.Angle(np.arcsin(zz), unit=u.radian)
# if 'phi' in kwargs:
# phi = np.rad2deg(np.arctan2(cosmu * sini,
# (-sinmu * sinnu * sini + cosnu * cosi)*cosnu))
# return (ra, dec, phi)
# else:
# return (ra, dec)
return ac.ICRS(ra=ra, dec=dec).transform_to(icrs_frame)
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@ac.frame_transform_graph.transform(ac.FunctionTransform, ac.ICRS, SDSSMuNu)
def radec_to_munu(icrs_frame, munu):
"""Convert from equatorial coordinates to SDSS great circle coordinates.
Parameters
----------
icrs_frame : :class:`~astropy.coordinates.ICRS`
Equatorial coordinates (RA, Dec).
Returns
-------
:class:`~pydl.pydlutils.coord.SDSSMuNu`
SDSS great circle coordinates (mu, nu).
"""
# from pydlutils.coord import stripe_to_eta
# from pydlutils.goddard.misc import cirrange
# if 'stripe' in kwargs:
# node = 95.0
# incl = stripe_to_incl(kwargs['stripe'])
# elif 'node' in kwargs and 'incl' in kwargs:
# node = kwargs['node']
# incl = kwargs['incl']
# else:
# raise ValueError('Must specify either STRIPE or NODE,INCL!')
# if ra.size != dec.size:
# raise ValueError('Number of elements in RA and DEC must agree!')
sinra = np.sin((icrs_frame.ra - munu.node).to(u.radian).value)
cosra = np.cos((icrs_frame.ra - munu.node).to(u.radian).value)
sindec = np.sin(icrs_frame.dec.to(u.radian).value)
cosdec = np.cos(icrs_frame.dec.to(u.radian).value)
sini = np.sin(munu.incl.to(u.radian).value)
cosi = np.cos(munu.incl.to(u.radian).value)
x1 = cosdec * cosra
y1 = cosdec * sinra
z1 = sindec
x2 = x1
y2 = y1 * cosi + z1 * sini
z2 = -y1 * sini + z1 * cosi
mu = ac.Angle(np.arctan2(y2, x2), unit=u.radian) + munu.node
nu = ac.Angle(np.arcsin(z2), unit=u.radian)
# if 'phi' in kwargs:
# sinnu = np.sin(np.deg2rad(nu))
# cosnu = np.cos(np.deg2rad(nu))
# sinmu = np.sin(np.deg2rad(mu-node))
# cosmu = np.cos(np.deg2rad(mu-node))
# phi = np.rad2deg(np.arctan2(cosmu * sini,
# (-sinmu * sinnu * sini + cosnu * cosi)*cosnu))
# return (ra, dec, phi)
# else:
# return (ra, dec)
return SDSSMuNu(mu=mu, nu=nu, stripe=munu.stripe)
[docs]
def stripe_to_eta(stripe):
"""Convert from SDSS great circle coordinates to equatorial coordinates.
Parameters
----------
stripe : :class:`int` or :class:`numpy.ndarray`
SDSS Stripe number.
Returns
-------
:class:`float` or :class:`numpy.ndarray`
The eta value in the SDSS (lambda,eta) coordinate system.
"""
stripe_sep = 2.5
eta = stripe * stripe_sep - 57.5
if stripe > 46:
eta -= 180.0
return eta
[docs]
def stripe_to_incl(stripe):
"""Convert from SDSS stripe number to an inclination relative to the
equator.
Parameters
----------
stripe : :class:`int` or :class:`numpy.ndarray`
SDSS Stripe number.
Returns
-------
:class:`float` or :class:`numpy.ndarray`
Inclination of the stripe relative to the equator (Dec = 0).
"""
dec_center = 32.5
eta_center = stripe_to_eta(stripe)
incl = eta_center + dec_center
return incl