def compute_piercings(ns, source_list, stations=None):
"""Creates nodes to compute the "piercing points" of each
source in source_list, for each antenna in array."""
stations = stations or Context.array.stations()
xyz = Context.array.xyz()
radec0 = Context.observation.phase_centre.radec()
# project our stations into an ionospheric coordinate system xyz1
# for now, we just project everything to z=0, and take station 1 as origin
for p in stations:
# xyz_proj gives positions projected to equatorial plane (z=0)
xyzp = ns.xyz_proj(p) << Meq.Paster(xyz(p), 0, index=2)
# xyz1 gives positions relative to station1
xyz1 = ns.xyz1(p) << xyzp - ns.xyz_proj(stations[0])
# and extract the xy1 component
ns.xy1(p) << Meq.Selector(xyz1, index=[0, 1], multi=True)
# if ionosphere is "stuck" to the sky, we need to rotate the antenna
# coordinates as we go along. Otherwise we need to rotate the piercing
# coordinates. The angle of rotation is given by the P.A. _at the
# projected antenna positions_.
if iono_rotate:
ns.pa0 << -Meq.ParAngle(xyz=ns.xyz_proj(stations[0]), radec=radec0)
ns.P0 << Jones.define_rotation_matrix(ns.pa0)
for p in stations:
# if ionosphere is stuck to the sky, rotate antenna coordinates by P0
if iono_rotate:
ns.xy_r(p) << Meq.MatrixMultiply(ns.P0, ns.xy1(p))
else:
# else create P (p/a rotation matrix)
ns.pa(p) << -Meq.ParAngle(xyz=ns.xyz_proj(p), radec=radec0)
ns.P(p) << Jones.define_rotation_matrix(ns.pa(p))
for src in source_list:
lm = src.direction.lm()
lm_sq = ns.lm_sq(src.name) << Meq.Sqr(lm)
# dxy is the relative X,Y coordinate of the piercing point for this source,
# relative to centre. In each direction it's to H*tg(alpha), where
# alpha is the direction of the source w.r.t. center (i.e., arccos l).
ns.dxy(src.name) << H * lm / Meq.Sqrt(1 - lm_sq)
# now compute absolute piercings per source, per antenna
for p in Context.array.stations():
if iono_rotate:
ns.pxy(src.name, p) << ns.xy_r(p) + ns.dxy(src.name)
else:
ns.pxy(src.name, p) << ns.xy1(p) + Meq.MatrixMultiply(
ns.P(p), ns.dxy(src.name))
return ns.pxy
def compute_piercings (ns,source_list,stations=None):
"""Creates nodes to compute the "piercing points" of each
source in source_list, for each antenna in array.""";
stations = stations or Context.array.stations();
xyz = Context.array.xyz();
radec0 = Context.observation.phase_centre.radec();
# project our stations into an ionospheric coordinate system xyz1
# for now, we just project everything to z=0, and take station 1 as origin
for p in stations:
# xyz_proj gives positions projected to equatorial plane (z=0)
xyzp = ns.xyz_proj(p) << Meq.Paster(xyz(p),0,index=2);
# xyz1 gives positions relative to station1
xyz1 = ns.xyz1(p) << xyzp - ns.xyz_proj(stations[0]);
# and extract the xy1 component
ns.xy1(p) << Meq.Selector(xyz1,index=[0,1],multi=True);
# if ionosphere is "stuck" to the sky, we need to rotate the antenna
# coordinates as we go along. Otherwise we need to rotate the piercing
# coordinates. The angle of rotation is given by the P.A. _at the
# projected antenna positions_.
if iono_rotate:
ns.pa0 << - Meq.ParAngle(xyz=ns.xyz_proj(stations[0]),radec=radec0);
ns.P0 << Jones.define_rotation_matrix(ns.pa0);
for p in stations:
# if ionosphere is stuck to the sky, rotate antenna coordinates by P0
if iono_rotate:
ns.xy_r(p) << Meq.MatrixMultiply(ns.P0,ns.xy1(p));
else:
# else create P (p/a rotation matrix)
ns.pa(p) << - Meq.ParAngle(xyz=ns.xyz_proj(p),radec=radec0);
ns.P(p) << Jones.define_rotation_matrix(ns.pa(p));
for src in source_list:
lm = src.direction.lm();
lm_sq = ns.lm_sq(src.name) << Meq.Sqr(lm);
# dxy is the relative X,Y coordinate of the piercing point for this source,
# relative to centre. In each direction it's to H*tg(alpha), where
# alpha is the direction of the source w.r.t. center (i.e., arccos l).
ns.dxy(src.name) << H*lm/Meq.Sqrt(1-lm_sq);
# now compute absolute piercings per source, per antenna
for p in Context.array.stations():
if iono_rotate:
ns.pxy(src.name,p) << ns.xy_r(p) + ns.dxy(src.name);
else:
ns.pxy(src.name,p) << ns.xy1(p) + Meq.MatrixMultiply(ns.P(p),ns.dxy(src.name));
return ns.pxy;
