• Weighting functions:

  Currently linear, Bessel and Gaussian weighting functions are supported. The width of the Bessel function is such that it should preserve all spatial information obtained by the telescope at the wavelength of observation, but suppress higher spatial frequencies. To minimise edge effects the Bessel function is truncated at a radius of 10 half-widths from the centre (although this is configurable), and apodized over its outer third by a cosine function. Viewed in frequency space the method consists of Fourier transforming the input dataset(s), multiplying the transform by a cylindrical top-hat (the F.T. of the Bessel function), then transforming back into image space. A linear weighting function is also available which works out to one half-width - this has the advantage that it is much faster to process and is much less susceptible to edge effects. The Gaussian weighting function is probably the best compromise between the Bessel (slow and prone to edge effects) and Linear (fast but the point spread function is non-trivial for modeling).

  The radius and size of ‘footprint’ for the weighting functions are configurable using the WTFNRAD and SCALE parameters.

• Splines:

  Additionally, spline interpolation and smoothing routines are also available. Note that the spline routines work on each integration in turn, whereas the weighting function routines work on all the input data in one go. At present the spline routines are experimental and comments are welcomed.

• Median:

  A regridding option derived from despike is available. This method simply puts all data points in an output grid and calculates the median of each output cell. Small pixel scales require large datasets (since not all cells in a 1 arcsecond grid will contain data points) although the Kappa commands fillbad and glitch can be used to smooth over bad pixels.

GUARD = LOGICAL (Read)

IN = CHAR (Read)

LAT_OUT = CHAR (Read)

LONG_OUT = CHAR (Read)

LOOP = LOGICAL (Read)

MSG_FILTER = CHAR (Read)

OUT = NDF (Write)

OUT_COORDS = CHAR (Read)

OUT_OBJECT = CHAR (Read)

PIXSIZE_OUT = REAL (Read)

REBIN_METHOD = CHAR (Read)

REF = CHAR (Read)

REFPIX ( 2 ) = INTEGER (Read)

TRIM = INTEGER (Read)

SCALE = REAL (Read)

SIZE ( 2 ) = INTEGER (Read)

SHIFT_DX = REAL (Read)

SHIFT_DY = REAL (Read)

TIMES = LOGICAL (Read)

WEIGHT = REAL (Read)

WEIGHTS = LOGICAL (Read)

WTFNRAD = INTEGER (Read)

rebin rebin_method=LINEAR out_coords=RJ

rebin rebin_method=BESSEL out=map out_coords=NA

rebin noloop accept ref=test.bat out=rebin

• The application can read in up to 256 separate input datasets.

• The output map will be large enough to include all data points.

• Spline regridding may have problems with SCAN/MAP (since integrations contain lots of overlapping data points).

• SCUBA sections can be given along with any input NDF

• The relative weights associated with each point in the output map are stored in a WEIGHTS NDF in the REDS extension of the output data (For WEIGHTS=TRUE). For spline rebinning each point is equivalent to the number of integrations added into the final data point. For weight function regridding the situation is more complicated. The actual number of points contributing to each cell can be stored using the TIMES parameter.

• Bolometer weights will be used if a BOLWT extension is found in the input data file (usually set with setbolwt).

• Astrometry information is stored in the WCS component and not the FITS extension.

Note that the parameters are position dependent and are not necessary. Missing parameters are requested. This means it is not possible to specify SHIFT_DX (position 3) without specifying the WEIGHT. If the file has the .txt extension the NDF system will attempt to convert it to NDF format before processing – this is probably not what you want.