AXES( ) = _INTEGER (Read)
axis or axes to remain in the output NDF. The slice will therefore contain an array
comprising all the elements along these axes. The maximum number of axes is one fewer
than the number of WCS axes in the NDF.
Each axis can be specified using one of the following options.
Its integer index within the current Frame of the input NDF (in the range 1 to the
number of axes in the current Frame).
Its Symbol string such as
A generic option where
"SPEC" requests the spectral axis,
"TIME" selects the time axis,
"SKYLAT" picks the sky longitude and latitude axes respectively. Only
those axis domains present are available as options.
A list of acceptable values is displayed if an illegal value is supplied. If the axes
of the current Frame are not parallel to the NDF pixel axes, then the pixel axis which
is most nearly parallel to the specified current Frame axis will be used.
Name of a text file containing the co-ordinates of slices to
be plucked. It is only accessed if Parameter MODE is given the value
Each line should contain the formatted axis values for a single position, in
the current Frame of the NDF. Axis values can be separated by spaces, tabs or
commas. The file may contain comment lines with the first character
CONTAINER = _LOGICAL (Read)
TRUE, each slice extracted is written as an
NDF component of the HDS container file specified by the OUT parameter. The
th component will
be named PLUCK_.
FALSE, each extraction is written to a separate file. On-the-fly format
conversion to foreign formats is not possible when CONTAINER=
= _LOGICAL (Read)
If TRUE, a detailed description of the co-ordinate Frame in which
the fixed co-ordinates are to be supplied is displayed before the positions
themselves. It is ignored if MODE=
INCAT = FILENAME
A catalogue containing a positions list giving the co-ordinates of the
fixed positions, such as produced by applications CURSOR
only accessed if Parameter MODE is given the value
. The catalogue
should have a WCS Frame common with the NDF, so that the NDF and catalogue
FrameSets can be aligned.
The mode in which the initial
co-ordinates are to be obtained. The supplied string can be one of the following
"Interface" –- positions are obtained using Parameter POS.
"Catalogue" –- positions are obtained from a positions list using Parameter
"File" –- positions are obtained from a text file using Parameter COIN.
IN = NDF (Read)
The NDF structure containing the data to be
extracted. It must have at least two dimensions.
METHOD = LITERAL (Read)
method to use when sampling the input pixel values. For details of these schemes, see
the descriptions of routine AST_RESAMPLEx
. METHOD can take the following
"Linear" –- When resampling, the output pixel values are calculated by linear
interpolation in the input NDF among the two nearest pixel values along each axis
chosen by AXES. This method produces smoother output NDFs than the nearest-neighbour
scheme, but is marginally slower.
"Sinc" –- Uses the
is the pixel offset from the interpolation point and
of this scheme is not recommended.
"SincSinc" –- Uses the
kernel. A valuable general-purpose scheme, intermediate in its visual effect on NDFs
between the linear option and using the nearest neighbour.
"SincCos" –- Uses the
kernel. Gives similar results to the
"SincGauss" –- Uses the
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
is the pixel offset from the interpolation point, and
the first-order Bessel function of the first kind. This scheme is similar to the
"SombCos" –- Uses the
kernel. This scheme is similar to the
"BlockAve" –- Block averaging over all pixels in the surrounding
All methods propagate variances from input to output, but the variance estimates
produced by interpolation schemes need to be treated with care since the spatial
smoothing produced by these methods introduces correlations variance estimates. The
initial default is
OUT = NDF (Write)
The name for the
output NDF, or the name of the single container file if CONTAINER=
PARAMS( 2 )
= _DOUBLE (Read)
An optional array which consists of additional parameters
required by the Sinc, SincSinc, SincCos, SincGauss, Somb, SombCos, and Gauss
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.
PARAMS(2) is required only by the SombCos, Gauss, 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
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.
The minimum value is
0.1, and the run-time default is
1.0. On astronomical
images 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. 
POS( ) = LITERAL (Read)
An the co-ordinates
of the next slice to be extracted, in the current co-ordinate Frame of the
NDF (supplying a colon
will display details of the current co-ordinate
Frame). The position should be supplied as a list of formatted axis values
separated by spaces or commas. POS is only accessed if Parameter MODE is given the
. If the co-ordinates are supplied on the command line only
one slice will be extracted; otherwise the application will ask for further
positions which may be terminated by supplying the null value (
= LITERAL (Read)
A Title for every output NDF structure. A null value (
propagates the title from the input NDF to all output NDFs.
TOL = _DOUBLE
The maximum tolerable geometrical distortion that may be introduced as
a result of approximating non-linear Mappings by a set of piece-wise linear
transforms. Both algorithms approximate non-linear co-ordinate transformations in
order to improve performance, and this parameter controls how inaccurate the
resulting approximation is allowed to be, as a displacement in pixels of the
input NDF. A value of zero will ensure that no such approximation is done, at
the expense of increasing execution time.