def create_w_term_like(im: Image,
w,
phasecentre=None,
remove_shift=False,
dopol=False) -> Image:
"""Create an image with a w term phase term in it:
.. math::
I(l,m) = e^{-2 \\pi j (w(\\sqrt{1-l^2-m^2}-1)}
The vis phasecentre is used as the delay centre for the w term (i.e. where n==0)
:param phasecentre:
:param im: template image
:param w: w value to evaluate (default is median abs)
:param remove_shift:
:param dopol: Do screen in polarisation?
:return: Image
"""
fim = copy_image(im)
fim_shape = list(im.shape)
if not dopol:
fim_shape[1] = 1
fim_array = numpy.zeros(fim_shape, dtype='complex')
fim = create_image_from_array(fim_array,
wcs=im.wcs,
polarisation_frame=im.polarisation_frame)
cellsize = abs(fim.wcs.wcs.cdelt[0]) * numpy.pi / 180.0
nchan, npol, _, npixel = fim_shape
if phasecentre is SkyCoord:
wcentre = phasecentre.to_pixel(im.wcs, origin=1) - 1.0
else:
wcentre = [im.wcs.wcs.crpix[0] - 1.0, im.wcs.wcs.crpix[1] - 1.0]
for chan in range(nchan):
for pol in range(npol):
fim.data[chan, pol, ...] = w_beam(npixel,
npixel * cellsize,
w=w,
cx=wcentre[0],
cy=wcentre[1],
remove_shift=remove_shift)
fov = npixel * cellsize
fresnel = numpy.abs(w) * (0.5 * fov)**2
log.debug(
'create_w_term_image: For w = %.1f, field of view = %.6f, Fresnel number = %.2f'
% (w, fov, fresnel))
return fim
def create_w_term_like(im: Image, w, phasecentre=None, **kwargs) -> Image:
"""Create an image with a w term phase term in it:
.. math::
I(l,m) = e^{-2 \\pi j (w(\\sqrt{1-l^2-m^2}-1)}
The vis phasecentre is used as the delay centre for the w term (i.e. where n==0)
:param phasecentre:
:param im: template image
:param w: w value to evaluate (default is median abs)
:return: Image
"""
fim = copy_image(im)
cellsize = abs(fim.wcs.wcs.cdelt[0]) * numpy.pi / 180.0
nchan, npol, _, npixel = fim.data.shape
if phasecentre is SkyCoord:
wcentre = phasecentre.to_pixel(im.wcs, origin=1)
else:
wcentre=[im.wcs.wcs.crpix[0], im.wcs.wcs.crpix[1]]
fim.data = numpy.zeros(fim.shape, dtype='complex')
remove_shift=get_parameter(kwargs, "remove_shift", False)
for chan in range(nchan):
for pol in range(npol):
fim.data[chan, pol,...] = w_beam(npixel, npixel * cellsize, w=w, cx=wcentre[0], cy=wcentre[1],
remove_shift=remove_shift)
fov = npixel * cellsize
fresnel = numpy.abs(w) * (0.5 * fov) ** 2
log.debug('create_w_term_image: For w = %.1f, field of view = %.6f, Fresnel number = %.2f' % (w, fov, fresnel))
return fim
def test_w_kernel_beam(self):
assert_allclose(numpy.real(w_beam(5, 0.1, 0))[0, 0], 1.0)
self.assertAlmostEqualScalar(w_beam(5, 0.1, 100)[2, 2], 1)
self.assertAlmostEqualScalar(w_beam(10, 0.1, 100)[5, 5], 1)
self.assertAlmostEqualScalar(w_beam(11, 0.1, 1000)[5, 5], 1)