UNMAKECUBE - Produce simulated time series data from a regrided ACSIS data cube

Description:

This routine creates one or more time series cubes, spanned by (frequency, detector number, time) axes, from one or more input sky cubes spanned by (celestial longitude, celestial latitude, spectrum) axes. Thus, it performs a sort of inverse to the MAKECUBE application.

The output time series detector samples are created by interpolating the supplied input sky cubes at the position of the reference time series sample centre. Various interpolation methods can be used (see parameter INTERP).

The output time series cubes inherit all meta-data from the corresponding input reference time series. The only thing modified is the values in the NDF "Data" array.

Parameters:

DETECTORS = LITERAL (Read)

A group of detector names. Only data for the named detectors will be included in the output time series cubes. If a null (!) value is supplied, data for all detectors will be created. [!]

IN = NDF (Read)

A group of input (ra,dec,spectrum) sky cubes (for instance, a set of tiles produced by MAKECUBE). If these sky cubes have any spatial overlap, then the output time series data will be derived from the last supplied sky cube that covers the overlap region. That is, sky cubes near the end of the supplied group take precedence over those near the start.

INTERP = LITERAL (Read)

The method to use when resampling the input sky cube pixel values. For details of these schemes, see the descriptions of routines AST_RESAMPLEx in SUN/210. INTERP can take the following values:

• "Linear" - The output sample values are calculated by bi-linear interpolation among the four nearest pixels values in the input sky cube. Produces smoother output NDFs than the nearest-neighbour scheme, but is marginally slower.

• "Nearest" - The output sample values are assigned the value of the single nearest input pixel. A very fast method.

• "Sinc" - Uses the sinc(pi$*$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$*$x)sinc(k$*$pi$*$x) kernel. A valuable general-purpose scheme, intermediate in its visual effect on NDFs between the bi-linear and nearest-neighbour schemes.

• "SincCos" - Uses the sinc(pi$*$x)cos(k$*$pi$*$x) kernel. Gives similar results to the "Sincsinc" scheme.

• "SincGauss" - Uses the sinc(pi$*$x)exp(-k$*$x$*$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$*$x) kernel, where x is the pixel offset from the interpolation point and somb(z)=2$*$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$*$x)cos(k$*$pi$*$x) kernel. This scheme is similar to the "SincCos" scheme.

[current value]

MSG_FILTER = _CHAR (Read)

Control the verbosity of the application. Values can be NONE (no messages), QUIET (minimal messages), NORMAL, VERBOSE, DEBUG or ALL. [NORMAL]

OUT = NDF (Write)

A group of output NDFs into which the simulated time series data will be written.

PARAMS( 2 ) = _DOUBLE (Read)

An optional array which consists of additional parameters required by the Sinc, SincSinc, SincCos, SincGauss, Somb and SombCos interpolation schemes (see parameter INTERP).

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 point 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 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 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. 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. []

REF = NDF (Read)

A group of existing time series data cubes. These act as templates for the new time series cubes created by this application, and specified via parameter OUT.

USEDETPOS = _LOGICAL (Read)

If a true value is supplied, then the detector positions are read from the detector position arrays in each template NDF. Otherwise, the detector positions are calculated on the basis of the FPLANEX/Y arrays. Both methods should (in the absence of bugs) result in identical cubes. [TRUE]

Related Applications

SMURF: MAKECUBE