from africanus.experimental.rime.fused.terms.core import Term
[docs]
class FeedRotation(Term):
"""Feed Rotation Term"""
def __init__(self, configuration, feed_type, corrs):
if configuration not in {"left", "right"}:
raise ValueError(
f"FeedRotation configuration must "
f"be either 'left' or 'right'. "
f"Got {configuration}"
)
if feed_type not in {"linear", "circular"}:
raise ValueError(
f"FeedRotation feed_type must be "
f"either 'linear' or 'circular'. "
f"Got {feed_type}"
)
if len(corrs) != 4:
raise ValueError(
f"Four correlations required for "
f"feed rotation but {corrs} were "
f"specified"
)
super().__init__(configuration)
self.feed_type = feed_type
def init_fields(self, typingctx, feed_parangle):
def dummy(feed_parangle):
pass
return [], dummy
def dask_schema(self, feed_parangle):
return {}
def sampler(self):
left = self.configuration == "left"
linear = self.feed_type == "linear"
def feed_rotation(state, s, r, t, f1, f2, a1, a2, c):
a = state.antenna1_index[r] if left else state.antenna2_index[r]
f = state.feed1_index[r] if left else state.feed2_index[r]
sin_a = state.feed_parangle[t, f, a, 0, 0]
cos_a = state.feed_parangle[t, f, a, 0, 1]
sin_b = state.feed_parangle[t, f, a, 1, 0]
cos_b = state.feed_parangle[t, f, a, 1, 1]
# https://casa.nrao.edu/aips2_docs/notes/185/node6.html
if linear:
return cos_a, sin_a, -sin_b, cos_b
else:
# e^{ix} = cos(x) + i.sin(x)
return (
0.5 * ((cos_a + cos_b) - (sin_a + sin_b) * 1j),
0.5 * ((cos_a - cos_b) + (sin_a - sin_b) * 1j),
0.5 * ((cos_a - cos_b) - (sin_a - sin_b) * 1j),
0.5 * ((cos_a + cos_b) + (sin_a + sin_b) * 1j),
)
return feed_rotation