Source code for pymap3d.vallado

#!/usr/bin/env python

# Copyright (c) 2014-2018 Michael Hirsch, Ph.D.
#
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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)