def radec2azel(self, mjd, ra, dec):
"""
Given RA/Dec and time returns Az/El.
Parameters
----------
mjd : float
Date in MJD.
ra : float
Right ascension in radian.
dec : float
Declination in radian.
Returns
----------
az : float
Azimuth in radian.
el : float
Elevation in radian.
"""
amprms = slalib.sla_mappa(self.epequi, mjd)
self.aoprms = slalib.sla_aoppat(mjd, self.aoprms)
ra_app, dec_app = slalib.sla_mapqkz(ra, dec, amprms)
az, zd, a, b, c = slalib.sla_aopqk(ra_app, dec_app, self.aoprms)
el = np.pi / 2 - zd
return az, el
def azel2radecpa(self, mjd, az, el):
"""
Given Az/El and time returns RA/Dec and parallactic angle.
This routine does not return a precisely correct parallactic angle.
Parameters
----------
mjd : float
Date in MJD.
az : float
Azimuth in radian.
el : float
Elevation in radian.
Returns
----------
ra : float
Right ascension in radian.
dec : float
Declination in radian.
pa : float
Parallactic angle in radian.
"""
zd = np.pi / 2 - el
amprms = slalib.sla_mappa(self.epequi, mjd)
self.aoprms = slalib.sla_aoppat(mjd, self.aoprms)
ra_app1, dec_app1 = slalib.sla_oapqk('a', az, zd + 1e-8, self.aoprms)
ra1, dec1 = slalib.sla_ampqk(ra_app1, dec_app1, amprms)
ra_app2, dec_app2 = slalib.sla_oapqk('a', az, zd - 1e-8, self.aoprms)
ra2, dec2 = slalib.sla_ampqk(ra_app2, dec_app2, amprms)
pa = slalib.sla_dbear(ra1, dec1, ra2, dec2)
ra = 0.5 * (ra1 + ra2)
dec = 0.5 * (dec1 + dec2)
return ra, dec, pa
def calculate_airmass_at_times(times, target, obs_latitude, obs_longitude,
obs_height):
""" Returns the airmass values at each of the times passed in for the given target
Returns the airmass values for a target and observer specified at each time value
in the input times list. This uses the speedier slalib aop quick function which caches the object lat/lon/height and
refraction parameters.
Args:
times (list): A list of datetimes during which to calculate the airmass of the target
target (dict): A dictionary of target details in the rise-set library format
obs_latitude (Angle): The site/observer latitude within a rise-set Angle
obs_longitude (Angle): The site/observer longitude within a rise-set Angle
obs_height (float): The site/observer altitude in meters
Returns:
list: A list of airmass values that correspond to the input list of datetimes
"""
airmasses = []
aop_params = None
# Assume standard atmosphere
temp_k = 273.15 # local ambient temperature (K; std=273.15)
pres_mb = 1013.25 # local atmospheric pressure (mb; std=1013.25D0)
rel_humid = 0.3 # local relative humidity (in the range 0D0-1D0)
wavelen = 0.55 # effective wavelength (in microns e.g. 0.55D0 (approx V band))
tlr = 0.0065 # tropospheric lapse rate (K per metre, e.g. 0.0065D0)
# Assume no polar motion
xp = yp = 0.0
# Assume UT1-UTC
dut = 0.0
site = {
'longitude': obs_longitude,
'latitude': obs_latitude,
'altitude': obs_height
}
for time in times:
mjd_utc = gregorian_to_ut_mjd(time)
if aop_params is None:
aop_params = sla.sla_aoppa(mjd_utc, dut,
obs_longitude.in_radians(),
obs_latitude.in_radians(), obs_height,
xp, yp, temp_k, pres_mb, rel_humid,
wavelen, tlr)
else:
aop_params = sla.sla_aoppat(mjd_utc, aop_params)
# Convert datetime to MJD_TDB
tdb = ut_mjd_to_tdb(mjd_utc) #not TDB but good enough
# Convert catalog mean RA, Dec at J2000 to apparent of date
if is_moving_object(target):
ra_apparent, dec_apparent = elem_to_topocentric_apparent(
time, target, site, target_to_jform(target))
else:
ra_apparent, dec_apparent = mean_to_apparent(target, tdb)
airmass = apparent_to_airmass(ra_apparent, dec_apparent, aop_params)
airmasses.append(airmass)
return airmasses