#!/usr/bin/env python
# Copyright (c) 2014-2018 Michael Hirsch, Ph.D.
#
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# 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
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"""
converts right ascension, declination to azimuth, elevation and vice versa.
Normally do this via AstroPy.
These functions are fallbacks for those who don't wish to use AstroPy (perhaps Python 2.7 users).
Michael Hirsch implementation of algorithms from D. Vallado
"""
from __future__ import division
from numpy import sin, cos, degrees, radians, arcsin, arctan2, atleast_1d
#
from .datetime2hourangle import datetime2sidereal
[docs]def vazel2radec(az_deg, el_deg, lat_deg, lon_deg, t):
"""
convert azimuth, elevation to right ascension, declination
Inputs
az_deg
Numpy ndarray of azimuth to point [degrees]
el_deg
Numpy ndarray of elevation to point [degrees]
lat_deg
scalar observer WGS84 latitude [degrees]
lon_deg
scalar observer WGS84 longitude [degrees]
t
time of observation
Outputs
ra_deg
Numpy ndarray of right ascension values [degrees]
dec_deg
Numpy ndarray of declination values [degrees]
from D.Vallado Fundamentals of Astrodynamics and Applications
p.258-259
"""
az_deg = atleast_1d(az_deg)
el_deg = atleast_1d(el_deg)
lat_deg = atleast_1d(lat_deg)
lon_deg = atleast_1d(lon_deg)
assert az_deg.shape == el_deg.shape, 'az and el must be same shape ndarray'
assert lat_deg.size == 1 and lon_deg.size == 1, 'need one observer and one or more (az,el).'
az = radians(az_deg)
el = radians(el_deg)
lat = radians(lat_deg)
lon = radians(lon_deg)
# %% Vallado "algorithm 28" p 268
dec = arcsin(sin(el) * sin(lat) + cos(el) * cos(lat) * cos(az))
lha = arctan2(-(sin(az) * cos(el)) / cos(dec),
(sin(el) - sin(lat) * sin(dec)) / (cos(dec) * cos(lat)))
lst = datetime2sidereal(t, lon) # lon, ra in RADIANS
""" by definition right ascension \in [0,360) degrees """
return degrees(lst - lha) % 360, degrees(dec)
[docs]def vradec2azel(ra_deg,dec_deg,lat_deg,lon_deg,t):
"""
convert right ascension, declination to azimuth, elevation
Inputs
ra_deg
Numpy ndarray of right ascension values [degrees]
dec_deg
Numpy ndarray of declination values [degrees]
lat_deg
scalar observer WGS84 latitude [degrees]
lon_deg
scalar observer WGS84 longitude [degrees]
t
time of observation
Outputs
az_deg
Numpy ndarray of azimuth to point [degrees]
el_deg
Numpy ndarray of elevation to point [degrees]
from D. Vallado "Fundamentals of Astrodynamics and Applications "
4th Edition Ch. 4.4 pg. 266-268
"""
ra = radians(ra_deg)
dec = radians(dec_deg)
lat = radians(lat_deg)
lon = radians(lon_deg)
lst = datetime2sidereal(t, lon) #RADIANS
# %% Eq. 4-11 p. 267 LOCAL HOUR ANGLE
lha = lst - ra
# %% #Eq. 4-12 p. 267
el = arcsin(sin(lat) * sin(dec) + cos(lat) * cos(dec) * cos(lha) )
# %% combine Eq. 4-13 and 4-14 p. 268
az = arctan2( -sin(lha) * cos(dec) / cos(el),
( sin(dec) - sin(el) * sin(lat) ) / (cos(el)*cos(lat)) )
return degrees(az) % 360.0, degrees(el)