import numpy as np
import matplotlib.pyplot as plt
from astropy import units as u
from astropy.time import Time
from astropy.coordinates import SkyCoord, EarthLocation, AltAz
from astropy.coordinates import ICRS, Galactic, FK4, FK5
#Find Altitude and Azimuth at ARO of the zenith at DRAO
#Observatories
ARO = EarthLocation(lat=45.9555*u.deg, lon=-78.0730*u.deg, height=390*u.m)
DRAO = EarthLocation(lat=49.321*u.deg, lon=-119.624*u.deg, height=545*u.m)
midnight = Time('2015-9-01 00:00:00')
zenith = SkyCoord(AltAz,az=358.2*u.deg,alt=50.0*u.deg, obstime=midnight, location=DRAO)
ARO_coords = ARO.to_geocentric()
DRAO_coords = DRAO.to_geocentric()
print DRAO_coords
print ARO_coords
class Interferometer(object):
def __init__(self,
configuration_file,
centre_freq=1420e6, # Hz
sub_array=None,
):
self.frequency = centre_freq / u.s
self.wavelength = phys.c / self.frequency
self.ref_position = None
self.observer = None
arr_desc = {'names': ('name', 'east', 'north', 'up', 'location'),
'formats': ('S5', float, float, float, EarthLocation)}
self.antennas = recarray((0,), dtype=arr_desc)
array_config = self.read_config(configuration_file)
if 'reference' in array_config.keys():
self._set_reference_(array_config['reference'])
self.__ephem_observer__()
self._build_array_(array_config['antennas'])
# function to update with only selected antennas
if sub_array is not None:
self._extract_subarray_(sub_array)
# number of antennas
self.nr_antennas = len(self.antennas)
# number pair or baseline
self.nr_baselines = (self.nr_antennas * (self.nr_antennas - 1)) // 2
def __ephem_observer__(self):
lon = self.ref_position.geodetic[0].degree
lat = self.ref_position.geodetic[1].degree
alt = self.ref_position.geodetic[2].value
self.observer = ephem.Observer()
self.observer.lon = str(lon)
self.observer.lat = str(lat)
self.observer.elevation = alt
def read_config(self, filename):
"""Read array default .yaml file."""
with open(filename, "r") as stream:
data = yaml.safe_load(stream)
return data
def __return_value__(self, prefix, item):
if item.startswith(prefix):
return item.split('=')[-1].strip()
else:
return None
def _set_reference_(self, ref_position):
"""General Earth position for the Telescope"""
ref_LAT = Latitude(ref_position['latitude'],
u.degree,
copy=False)
ref_LON = Longitude(ref_position['longitude'],
u.degree,
wrap_angle=180. * u.degree,
copy=False)
ref_ALT = u.Quantity(ref_position['altitude'],
u.m,
copy=False)
self.ref_position = EarthLocation(lat=ref_LAT,
lon=ref_LON,
height=ref_ALT)
def _build_array_(self, antennas):
"""ENU coordinates per antenna"""
if self.ref_position is not None:
[x, y, z] = self.ref_position.to_geocentric()
self.antennas.resize(len(antennas))
for cnt, antenna in enumerate(antennas):
ant_ = [item.strip() for item in antenna.split(",")]
for item_ in ant_:
for prefix_ in ('name', 'east', 'north', 'up'):
val_ = self.__return_value__(prefix_, item_)
if val_ is not None:
self.antennas[cnt][prefix_] = val_
if self.ref_position is not None:
ant_North = x.value + self.antennas[cnt]['north']
ant_East = y.value + self.antennas[cnt]['east']
ant_Up = z.value + self.antennas[cnt]['up']
self.antennas[cnt]['location'] = EarthLocation(x=ant_North * u.m,
y=ant_East * u.m,
z=ant_Up * u.m)
def _extract_subarray_(self, subarray):
row_indices = []
for row_cnt, antenna in enumerate(self.antennas):
if antenna['name'] in subarray:
row_indices.append(row_cnt)
self.antennas = self.antennas[row_indices]
def baselines(self):
"""The function evaluates baselines lenghts
and the angle between antennas
"""
P = np.array([self.antennas['north'],
self.antennas['east']]).T
# antenna position in wavelength units
P = P / self.wavelength.value # baseline
bl_length = np.zeros((self.nr_baselines, ))
bl_az_angle = np.zeros((self.nr_baselines, ))
cnt = 0
for idx0 in range(self.nr_antennas):
for idx1 in range(idx0 + 1, self.nr_antennas):
bl_len_p0 = (P[idx0, 0] - P[idx1, 0])**2
bl_len_p1 = (P[idx0, 1] - P[idx1, 1])**2
bl_length[cnt] = np.sqrt(bl_len_p0 + bl_len_p1)
bl_az_angle[cnt] = np.arctan2((P[idx0, 1] - P[idx1, 1]),
(P[idx0, 0] - P[idx1, 0]))
cnt += 1
return bl_length, bl_az_angle
