Change the values in a vector catalogue
"
ChangeColVals"
the name of an existing column must be supplied (a list of available
column names is displayed if a non-existent column name is given). If parameter MODE is "
AddColumn"
the name of the new column must be supplied (an error will be reported if the
column already exists). "
RA"
] "
DEC"
] "
AddColumn"
. The suggested default is the Label value
from the NDF specified by parameter NDF. "
Debias"
. It gives the type of bias estimator to use when
creating the new P and PI values, using the nomeclature of Montier at al "
Polarization
measurements analysis II. Best estimators of polarization fraction and angle"
(A&A, 2018):
"
AS"
: The asymptotic estimator. See section 2.3 of Montier et al. This estimator produces bad P and
PI values if the squared PI value is less than the variance in PI.
"
MAS"
: The modified asymptotic estimator. See section 2.5 of Montier et al. This estimator does not
produces bad P and PI values, even if the squared PI value is less than the variance in
PI.
"
None"
: No de-bising is applied.
"
AddColumn"
). If
parameter MASKCOL is FALSE (the default), the NDF’
s pixel array is sampled at the
positions given in the catalogue columns specified by parameters COL1 and COL2, using
the interpolation method specified by parameter METHOD, and the sampled values are
stored in the new column. The data type of the new column is set to the data type of the
NDF. If parameter MASKCOL is TRUE, the new column holds integer values - 1 if the
corresponding pixel in the NDF array is good and 0 otherwise. Parameters COL1 and COL2
again specify the catalogue columns that hold the position for each row. The nearest pixel
to the resulting position is tested by comparing it with the appropriate Starlink "
bad"
value. [FALSE] "
ChangeColVals"
or "
AddColumn"
. It gives the method to use when sampling the NDF pixel
array to generate the new catalogue column values. For details on these schemes, see the
descriptions of routines AST_RESAMPLEx in SUN/210. METHOD can take the following
values.
"
Bilinear"
– The new column values are calculated by bi-linear interpolation among the four nearest
pixels values in the input NDF. Produces smoother output NDFs than the nearest-neighbour scheme,
but is marginally slower.
"
Nearest"
– The new column values are assigned the value of the single nearest input
pixel.
"
Sinc"
– The new column values are calculated using the
sinc(pi$\ast $x)
kernel, where x is the pixel offset from the interpolation point and sinc(z)=sin(z)/z. Use of this scheme
is not recommended.
"
SincSinc"
– Uses the sinc(pi$\ast $x)sinc(k$\ast $pi$\ast $x)
kernel. A valuable general-purpose scheme, intermediate in its visual effect between the bilinear and
nearest-neighbour schemes.
"
SincCos"
– Uses the sinc(pi$\ast $x)cos(k$\ast $pi$\ast $x)
kernel. Gives similar results to the "
Sincsinc"
scheme.
"
SincGauss"
– Uses the sinc(pi$\ast $x)exp(-k$\ast $x$\ast $x)
kernel. Good results can be obtained by matching the FWHM of the envelope function to the
point-spread function of the input data (see Parameter PARAMS).
"
Somb"
– Uses the somb(pi$\ast $x)
kernel, where x is the pixel offset from the interpolation point and
somb(z)=2$\ast $J1(z)/z
(J1 is the first-order Bessel function of the first kind. This scheme is similar to the "
Sinc"
scheme.
"
SombCos"
– Uses the somb(pi$\ast $x)cos(k$\ast $pi$\ast $x)
kernel. This scheme is similar to the "
SincCos"
scheme.
"
Gauss"
– Uses the exp(-k$\ast $x$\ast $x)
kernel. The FWHM of the Gaussian is given by Parameter PARAMS(2), and the point at which to
truncate the Gaussian to zero is given by Parameter PARAMS(1).
The initial default is "
Nearest"
. [current value]
"
AddColumn"
: A new column is added to the catalogue. The name of the new column is given by
parameter COL. The values to store in the column are obtained from the NDF specified by parameter
NDF in a manner determined by parameter MASKCOL.
"
Debias"
: New debiased values are written to the P (percentage polarisation) and PI (polarised
intensity) columns based on the values in the Q, U, I and DPI columns. The form of de-biasing to use
is specified by parameter DEBIASTYPE. This option is the same as the "
Recalc"
option except that
only the P and PI columns are recalculated.
"
ChangeColVals"
: The values in the column specified by parameter COL are changed to the values
read from the NDF specified by parameter NDF. The NDF is sampled at the positions stored in the
catalogue columns specified by parameters COL1 and COL2, using the interpolation method specified
by parameter METHOD.
"
Recalc"
: All columns that are derived from the Stokes parameter columns are re-calculated. In other
words, the P, PI, ANG, DP, DPI and DANG columns are recalculated on the basis of the curent values
in the I, Q, U, DI, DQ and DU columns. The form of de-biasing to use is specified by parameter
DEBIASTYPE.
"
ChangeColVals"
or "
AddColumn"
. PARAMS( 1 ) is required by all the above schemes. It is used to specify how many pixels are to contribute to the interpolated result on either side of the interpolation in each dimension. Typically, a value of 2 is appropriate and the minimum allowed value is 1 (i.e. one pixel on each side). A value of zero or fewer indicates that a suitable number of pixels should be calculated automatically. [0]
PARAMS( 2 ) is required only by the Gauss, SombCos, SincSinc, SincCos, and SincGauss schemes. For the SombCos, SincSinc and SincCos schemes, it specifies the number of pixels at which the envelope of the function goes to zero. The minimum value is 1.0, and the run-time default value is 2.0. For the Gauss and SincGauss scheme, it specifies the full-width at half-maximum (FWHM) of the Gaussian envelope measured in output pixels. The minimum value is 0.1, and the run-time default is 1.0. On astronomical NDFs and spectra, good results are often obtained by approximately matching the FWHM of the envelope function, given by PARAMS(2), to the point-spread function of the input data. []
"
AddColumn"
. The
suggested default is the Units value from the NDF specified by parameter NDF. The input catalogue must contain WCS information (i.e. it must have been created using polpack).