def _pvobs(self):
'''calculates position and velocity of the observatory
returns position/velocity in AU and AU/d in GCRS reference frame
'''
# convert obs position from WGS84 (lat long) to ITRF geocentric coords in AU
xyz = self.location.to(u.AU).value
# now we need to convert this position to Celestial Coords
# specifically, the GCRS coords.
# conversion from celestial to terrestrial coords given by
# [TRS] = RPOM * R_3(ERA) * RC2I * [CRS]
# where:
# [CRS] is vector in GCRS (geocentric celestial system)
# [TRS] is vector in ITRS (International Terrestrial Ref System)
# ERA is earth rotation angle
# RPOM = polar motion matrix
tt = self.tt
mjd = self.utc.mjd
# we need the IERS values to correct for the precession/nutation of the Earth
iers_tab = IERS.open()
# Find UT1, which is needed to calculate ERA
# uses IERS_B by default , for more recent times use IERS_A download
try:
ut1 = self.ut1
except:
try:
iers_a_file = download_file(IERS_A_URL, cache=True)
iers_a = IERS_A.open(iers_a_file)
self.delta_ut1_utc = self.get_delta_ut1_utc(iers_a)
ut1 = self.ut1
except:
# fall back to UTC with degraded accuracy
warnings.warn(
'Cannot calculate UT1: using UTC with degraded accuracy')
ut1 = self.utc
# Gets x,y coords of Celestial Intermediate Pole (CIP) and CIO locator s
# CIO = Celestial Intermediate Origin
# Both in GCRS
X, Y, S = erfa.xys00a(tt.jd1, tt.jd2)
# Get dX and dY from IERS B
dX = np.interp(mjd, iers_tab['MJD'], iers_tab['dX_2000A']) * u.arcsec
dY = np.interp(mjd, iers_tab['MJD'], iers_tab['dY_2000A']) * u.arcsec
# Get GCRS to CIRS matrix
# can be used to convert to Celestial Intermediate Ref Sys
# from GCRS.
rc2i = erfa.c2ixys(X + dX.to(u.rad).value, Y + dY.to(u.rad).value, S)
# Gets the Terrestrial Intermediate Origin (TIO) locator s'
# Terrestrial Intermediate Ref Sys (TIRS) defined by TIO and CIP.
# TIRS related to to CIRS by Earth Rotation Angle
sp = erfa.sp00(tt.jd1, tt.jd2)
# Get X and Y from IERS B
# X and Y are
xp = np.interp(mjd, iers_tab['MJD'], iers_tab['PM_x']) * u.arcsec
yp = np.interp(mjd, iers_tab['MJD'], iers_tab['PM_y']) * u.arcsec
# Get the polar motion matrix. Relates ITRF to TIRS.
rpm = erfa.pom00(xp.to(u.rad).value, yp.to(u.rad).value, sp)
# multiply ITRF position of obs by transpose of polar motion matrix
# Gives Intermediate Ref Frame position of obs
x, y, z = np.array([rpmMat.T.dot(xyz) for rpmMat in rpm]).T
# Functions of Earth Rotation Angle, theta
# Theta is angle bewtween TIO and CIO (along CIP)
# USE UT1 here.
theta = erfa.era00(ut1.jd1, ut1.jd2)
S, C = np.sin(theta), np.cos(theta)
# Position #GOT HERE
pos = np.asarray([C * x - S * y, S * x + C * y, z]).T
# multiply by inverse of GCRS to CIRS matrix
# different methods for scalar times vs arrays
if pos.ndim > 1:
pos = np.array(
[np.dot(rc2i[j].T, pos[j]) for j in range(len(pos))])
else:
pos = np.dot(rc2i.T, pos)
# Velocity
vel = np.asarray(
[SR * (-S * x - C * y), SR * (C * x - S * y),
np.zeros_like(x)]).T
# multiply by inverse of GCRS to CIRS matrix
if vel.ndim > 1:
vel = np.array(
[np.dot(rc2i[j].T, vel[j]) for j in range(len(pos))])
else:
vel = np.dot(rc2i.T, vel)
#return position and velocity
return pos, vel
def _pvobs(self):
'''calculates position and velocity of the observatory
returns position/velocity in AU and AU/d in GCRS reference frame
'''
# convert obs position from WGS84 (lat long) to ITRF geocentric coords in AU
xyz = self.location.to(u.AU).value
# now we need to convert this position to Celestial Coords
# specifically, the GCRS coords.
# conversion from celestial to terrestrial coords given by
# [TRS] = RPOM * R_3(ERA) * RC2I * [CRS]
# where:
# [CRS] is vector in GCRS (geocentric celestial system)
# [TRS] is vector in ITRS (International Terrestrial Ref System)
# ERA is earth rotation angle
# RPOM = polar motion matrix
tt = self.tt
mjd = self.utc.mjd
# we need the IERS values to correct for the precession/nutation of the Earth
iers_tab = IERS.open()
# Find UT1, which is needed to calculate ERA
# uses IERS_B by default , for more recent times use IERS_A download
try:
ut1 = self.ut1
except:
try:
iers_a_file = download_file(IERS_A_URL, cache=True)
iers_a = IERS_A.open(iers_a_file)
print "Trying to download...", iers_a_file
self.delta_ut1_utc = self.get_delta_ut1_utc(iers_a)
ut1 = self.ut1
except:
# fall back to UTC with degraded accuracy
warnings.warn('Cannot calculate UT1: using UTC with degraded accuracy')
ut1 = self.utc
# Gets x,y coords of Celestial Intermediate Pole (CIP) and CIO locator s
# CIO = Celestial Intermediate Origin
# Both in GCRS
X,Y,S = erfa.xys00a(tt.jd1,tt.jd2)
# Get dX and dY from IERS B
dX = np.interp(mjd, iers_tab['MJD'], iers_tab['dX_2000A']) * u.arcsec
dY = np.interp(mjd, iers_tab['MJD'], iers_tab['dY_2000A']) * u.arcsec
# Get GCRS to CIRS matrix
# can be used to convert to Celestial Intermediate Ref Sys
# from GCRS.
rc2i = erfa.c2ixys(X+dX.to(u.rad).value, Y+dY.to(u.rad).value, S)
# Gets the Terrestrial Intermediate Origin (TIO) locator s'
# Terrestrial Intermediate Ref Sys (TIRS) defined by TIO and CIP.
# TIRS related to to CIRS by Earth Rotation Angle
sp = erfa.sp00(tt.jd1,tt.jd2)
# Get X and Y from IERS B
# X and Y are
xp = np.interp(mjd, iers_tab['MJD'], iers_tab['PM_x']) * u.arcsec
yp = np.interp(mjd, iers_tab['MJD'], iers_tab['PM_y']) * u.arcsec
# Get the polar motion matrix. Relates ITRF to TIRS.
rpm = erfa.pom00(xp.to(u.rad).value, yp.to(u.rad).value, sp)
# multiply ITRF position of obs by transpose of polar motion matrix
# Gives Intermediate Ref Frame position of obs
x,y,z = np.array([rpmMat.T.dot(xyz) for rpmMat in rpm]).T
# Functions of Earth Rotation Angle, theta
# Theta is angle bewtween TIO and CIO (along CIP)
# USE UT1 here.
theta = erfa.era00(ut1.jd1,ut1.jd2)
S,C = np.sin(theta),np.cos(theta)
# Position #GOT HERE
pos = np.asarray([C*x - S*y, S*x + C*y, z]).T
# multiply by inverse of GCRS to CIRS matrix
# different methods for scalar times vs arrays
if pos.ndim > 1:
pos = np.array([np.dot(rc2i[j].T,pos[j]) for j in range(len(pos))])
else:
pos = np.dot(rc2i.T,pos)
# Velocity
vel = np.asarray([SR*(-S*x - C*y), SR*(C*x-S*y), np.zeros_like(x)]).T
# multiply by inverse of GCRS to CIRS matrix
if vel.ndim > 1:
vel = np.array([np.dot(rc2i[j].T,vel[j]) for j in range(len(pos))])
else:
vel = np.dot(rc2i.T,vel)
#return position and velocity
return pos,vel
def gcrs_posvel_from_itrf(loc, toas, obsname="obs"):
"""Return a list of PosVel instances for the observatory at the TOA times.
Observatory location should be given in the loc argument as an astropy
EarthLocation object. This location will be in the ITRF frame (i.e.
co-rotating with the Earth).
The optional obsname argument will be used as label in the returned
PosVel instance.
This routine returns a list of PosVel instances, containing the
positions (m) and velocities (m / s) at the times of the toas and
referenced to the Earth-centered Inertial (ECI, aka GCRS) coordinates.
This routine is basically SOFA's pvtob() [Position and velocity of
a terrestrial observing station] with an extra rotation from c2ixys()
[Form the celestial to intermediate-frame-of-date matrix given the CIP
X,Y and the CIO locator s].
"""
unpack = False
# If the input is a single TOA (i.e. a row from the table),
# then put it into a list
if type(toas) == table.row.Row:
ttoas = Time([toas["mjd"]])
unpack = True
elif type(toas) == table.table.Table:
ttoas = toas["mjd"]
elif isinstance(toas, Time):
if toas.isscalar:
ttoas = Time([toas])
unpack = True
else:
ttoas = toas
else:
if np.isscalar(toas):
ttoas = Time([toas], format="mjd")
unpack = True
else:
ttoas = toas
N = len(ttoas)
if len(ttoas.shape) != 1:
raise ValueError("At most one-dimensional array of times possible, "
"shape was {}".format(ttoas.shape))
# Get various times from the TOAs as arrays
tts = np.asarray([(t.jd1, t.jd2) for t in ttoas.tt]).T
ut1s = np.asarray([(t.jd1, t.jd2) for t in ttoas.ut1]).T
mjds = np.asarray(ttoas.mjd)
iers_b = get_iers_b_up_to_date(mjds.max())
# Get x, y coords of Celestial Intermediate Pole and CIO locator s
X, Y, S = erfa.xys00a(*tts)
# Get dX and dY from IERS A in arcsec and convert to radians
# dX = np.interp(mjds, iers_tab['MJD'], iers_tab['dX_2000A_B']) * asec2rad
# dY = np.interp(mjds, iers_tab['MJD'], iers_tab['dY_2000A_B']) * asec2rad
# Get dX and dY from IERS B in arcsec and convert to radians
dX = np.interp(mjds, iers_b["MJD"].to_value(u.d),
iers_b["dX_2000A"].to_value(u.rad))
dY = np.interp(mjds, iers_b["MJD"].to_value(u.d),
iers_b["dY_2000A"].to_value(u.rad))
# Get GCRS to CIRS matrices
rc2i = erfa.c2ixys(X + dX, Y + dY, S)
# Gets the TIO locator s'
sp = erfa.sp00(*tts)
# Get X and Y from IERS A in arcsec and convert to radians
# xp = np.interp(mjds, iers_tab['MJD'], iers_tab['PM_X_B']) * asec2rad
# yp = np.interp(mjds, iers_tab['MJD'], iers_tab['PM_Y_B']) * asec2rad
# Get X and Y from IERS B in arcsec and convert to radians
xp = np.interp(mjds, iers_b["MJD"].to_value(u.d),
iers_b["PM_x"].to_value(u.rad))
yp = np.interp(mjds, iers_b["MJD"].to_value(u.d),
iers_b["PM_y"].to_value(u.rad))
# Get the polar motion matrices
rpm = erfa.pom00(xp, yp, sp)
# Observatory geocentric coords in m
xyzm = np.array([a.to_value(u.m) for a in loc.geocentric])
x, y, z = np.dot(xyzm, rpm).T
# Functions of Earth Rotation Angle
theta = erfa.era00(*ut1s)
s, c = np.sin(theta), np.cos(theta)
sx, cx = s * x, c * x
sy, cy = s * y, c * y
# Initial positions and velocities
iposs = np.asarray([cx - sy, sx + cy, z]).T
ivels = np.asarray([OM * (-sx - cy), OM * (cx - sy), np.zeros_like(x)]).T
# There is probably a way to do this with np.einsum or something...
# and here it is .
poss = np.empty((N, 3), dtype=np.float64)
vels = np.empty((N, 3), dtype=np.float64)
poss = np.einsum("ij,ijk->ik", iposs, rc2i)
vels = np.einsum("ij,ijk->ik", ivels, rc2i)
r = PosVel(poss.T * u.m, vels.T * u.m / u.s, obj=obsname, origin="earth")
if unpack:
return r[0]
else:
return r