UNMAKEMAP - Produce simulated time series data from a SCUBA-2 map

Description:

This routine creates one or more simulated SCUBA-2 time series cubes, from a supplied 2D image of the sky. Thus, it performs a sort of inverse to the MAKEMAP application.

The output time series bolometer samples are created by interpolating the supplied input sky image at the position of the reference time series sample centre. Various interpolation methods can be used (see parameter INTERP). Gaussian noise may also be added (see parameter SIGMA).

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:

ANGROT = _DOUBLE (Read)

The angle from the focal plane X axis to the fixed analyser, in degrees. Measured positive in the same sense as rotation from focal plane X to focal plane Y. [90.0]

IN = NDF (Read)

The input 2D image of the sky. If NDFs are supplied for the QIN and UIN parameters, then IN should hold I values.

INTERP = LITERAL (Read)

The method to use when resampling the input sky image 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. These will hold _DOUBLE data vlues.

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. []

PAOFF = _DOUBLE (Read)

The angle from the fixed analyser to the have-wave plate for a POL_ANG value of zero, in degrees. Measured positive in the same sense as rotation from focal plane X to focal plane Y. [0.0]

PASIGN = _LOGICAL (Read)

Indicates the sense of rotation of the spinning half-wave plate. If TRUE, it is assumed that a positive POL_ANG value corresponds to rotation from focal plane X to focal plane Y axis. If FALSE, it is assumed that a positive POL_ANG value corresponds to rotation from focal plane Y to focal plane X axis. [TRUE]

QIN = NDF (Read)

The input 2D image of the sky Q values, with respect to the second pixel axis (i.e. the pixel Y axis). If QIN and UIN are both supplied, then the time series specified by the REF parameter should contain flat-fielded POL2 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. They should contain _DOUBLE (i.e. flat-fielded) data values.

SIGMA = _DOUBLE (Read)

The standard deviation of the Gaussian noise to add to the output data. [0.0]

UIN = NDF (Read)

The input 2D image of the sky U values, with respect to the second pixel axis (i.e. the pixel Y axis). If QIN and UIN are both supplied, then the time series specified by the REF parameter should contain flat-fielded POL2 data. [!]

USEAXIS = LITERAL (Read)

A set of 2 axes to be selected from the Current Frame in the sky map. Each axis can be specified either by giving its index within the Current Frame in the range 1 to the number of axes in the Frame, or by giving its symbol. This parameter is only accessed if the Current Frame in the supplied NDF has more than 2 axes. The dynamic default selects the axes with the same indices as the significant NDF axes.

Related Applications

SMURF: MAKEMAP