from __future__ import annotations
from typing import TYPE_CHECKING
import numpy as np
if TYPE_CHECKING:
from pyvisgen.simulation import Visibilities
__all__ = ["compute_single_stokes_component", "get_stokes_from_vis_data"]
[docs]
def get_stokes_from_vis_data(
vis_data: Visibilities, stokes_comp: str, polarization: str
):
"""Get the Stokes visibility for a given Stokes component
depending on polarization.
Parameters
----------
vis_data : pyvisgen.simulation.Visibilities
The Visibilities which are the output of the ``pyvisgen.simulation.vis_loop``
function.
stokes_comp : str
The name of the Stokes component which should be returned.
Valid names are: ``'I'``, ``'Q'``, ``'U'``, ``'V'``, ``'I+V'``,
``'Q+U'``, ``'Q-U'``, ``'I-V'``.
polarization : str
The type of polarization which should be considered.
Valid values are: ``'circular'`` and any value. In case this is not set to
``'circular'``, the result will be the same for all other values.
Returns
-------
numpy.ndarray:
The Stokes visibility of the given Stokes component with the given polarization.
"""
if polarization == "circular":
match stokes_comp:
case "I":
stokes_vis = compute_single_stokes_component(vis_data, 0, 3, "+")
case "Q":
stokes_vis = compute_single_stokes_component(vis_data, 1, 2, "+")
case "U":
stokes_vis = compute_single_stokes_component(vis_data, 1, 2, "-")
case "V":
stokes_vis = compute_single_stokes_component(vis_data, 0, 3, "-")
case "I+V":
stokes_vis = vis_data[..., 0, 0] + 1j * vis_data[..., 0, 1]
case "Q+U":
stokes_vis = vis_data[..., 1, 0] + 1j * vis_data[..., 1, 1]
case "Q-U":
stokes_vis = vis_data[..., 2, 0] + 1j * vis_data[..., 2, 1]
case "I-V":
stokes_vis = vis_data[..., 3, 0] + 1j * vis_data[..., 3, 1]
else:
match stokes_comp:
case "I":
stokes_vis = compute_single_stokes_component(vis_data, 0, 3, "+")
case "Q":
stokes_vis = compute_single_stokes_component(vis_data, 0, 3, "-")
case "U":
stokes_vis = compute_single_stokes_component(vis_data, 1, 2, "+")
case "V":
stokes_vis = compute_single_stokes_component(vis_data, 1, 2, "-")
case "I+Q":
stokes_vis = vis_data[..., 0, 0] + 1j * vis_data[..., 0, 1]
case "U+V":
stokes_vis = vis_data[..., 1, 0] + 1j * vis_data[..., 1, 1]
case "U-V":
stokes_vis = vis_data[..., 2, 0] + 1j * vis_data[..., 2, 1]
case "I-Q":
stokes_vis = vis_data[..., 3, 0] + 1j * vis_data[..., 3, 1]
return np.squeeze(stokes_vis)
[docs]
def compute_single_stokes_component(
vis_data: Visibilities,
stokes_comp_1: int,
stokes_comp_2: int,
sign: str,
):
"""Computes single stokes components I, Q, U, or V from visibility
data for gridding.
Parameters
----------
vis_data : :class:`~pyvisgen.simulation.Visibilities`
:class:`~pyvisgen.simulation.Visibilities` dataclass object
containing the visibilities measured by the array.
stokes_comp_1 : int
Index of first stokes visibility.
stokes_comp_2 : int
Index of second stokes visibility.
sign : str
Whether to add or subtract ``stokes_comp_1`` and ``stokes_comp_2``.
Valid values are ``'+'`` or ``'-'``.
Returns
-------
numpy.ndarray
The visibilities for the specified Stokes component.
"""
if sign not in "+-":
raise ValueError("'sign' can only be '+' or '-'!")
match sign:
case "+":
real = vis_data[..., stokes_comp_1, 0] + vis_data[..., stokes_comp_2, 0]
imag = vis_data[..., stokes_comp_1, 1] + vis_data[..., stokes_comp_2, 1]
case "-":
real = vis_data[..., stokes_comp_1, 0] - vis_data[..., stokes_comp_2, 0]
imag = vis_data[..., stokes_comp_1, 1] - vis_data[..., stokes_comp_2, 1]
return real + 1j * imag
