Program: SMOOTH Purpose: Smooth sets with a gaussian beam File: smooth.shl Author: M. Vogelaar Category: MANIPULATION, HEADER, FITTING Keywords: INSET= Give input set, subsets: Input set (and subsets). Maximum number of subsets is 2048. BOX= Frame for input subsets. [entire subset] OUTSET= Give output set (and subsets): Output set and subset(s) for the result. The number of output subsets is the same as the number of input sub- sets. ** CUTOFF= Give cutoff ratio for gaussian [1/10000] This is the ratio of the gaussian function values at central point and a point x on the boundary. AUTO= Automatic mode? [Y] In automatic mode, beam parameters of an old beam are, if possible, calculated from the header and new beam parameters are asked. Parameters of a convolution func- tion are calculated by the program, and are used as initialization for the iteration towards the new beam. In this mode you need the associated antenna pat- tern (AP). In non-automatic mode the user can give the convolution parameters directly. ** WRITECONV= Write convolution function to a set: Y/[N] Write 2-d gauss data used in convolution to a set (CONSET=) for further inspection f.i. OUTCONSET= Output set & subsets for conv. fie.: [none] Keyword is only asked if WRITECONV=Y DECIM= Give decimation: [1,1] There is an upper limit to the decimation, depending on the size of your input set. IN automatic MODE THE FOLLOWING KEYWORDS ARE ASKED: APSET= Give set (, subset) of antenna pattern: Input of the AP sub structure. Its dimension has to be 2. OUTAPSET= Output set (, subset) for AP: [none] OLDBEAM= Beam sizes old maj, min axes (arcsec): Size of major, minor axis (FWHM) of the original beam in arcsec if nothing was found in header. If values were found in the header of APSET=, these values are default and the keyword is asked hidden. OLDPOSANG= Position angle old beam (deg): Position angle in degrees of major axis wrt. the north in the direction of the east. If a value was found in the header of APSET=, this value is default and the keyword is asked hidden. NEWBEAM= Beam sizes new maj, min axes (arcsec): Wanted size of major, minor axis of smoothed new beam in arcsec. For one dimensional smoothing, give one of the axes the same value as the original axis and give the new position angle the same value as the old one. NEWPOSANG= Give position angle new beam (deg): Position angle in degrees of major axis of smoothed beam wrt. the north. ** FITBOX= Minimum size of convolved part of AP used in [11,11] a least squares fit. The sizes have to be odd and smal- ler than 127. The default values are the same as in the program ANTPAT. ** CLIP= Use data in fit with values above a user given [none] clip level. ** TOLERANCE= Give tolerance in least squares fit: [0.01] Fitting of the new beam stops when successive iterations fail to produce a decrement in reduced chi-squared less than TOLERANCE. If its value is less than the minimum tolerance possible, it will be set to this value. This means that maximum accuracy can be obtained by setting TOLERANCE=0.0. ** EPSILON= Give accuracy in fitted beam (%): [1] Stop iteration if calculated new beam sizes and wanted beam sizes don't differ more than epsilon (percentage!). ** PRESMOOTH= Only presmoothing? [N] (i.e. determine convolution parameters and scale factor only) ** SCALE= Scaling factor output subsets. [Calculated] The scaling factor used will be stored in the descriptor item SCALEFAC in the output subset(s). IN non-automatic MODE THE FOLLOWING KEYWORDS ARE ASKED: OLDBEAM= Beam sizes old maj, min axes (arcsec): [Header values] or: Beam sizes old maj, min axes (arcsec): [grid spacings] Size of major, minor axis (FWHM) of the original beam in arcsec. The default depends on the availability of header items BMMAJ en BMMIN in the header of INSET= OLDPOSANG= Position angle old beam (deg): [0] Position angle in degrees of major axis wrt. the north in the direction of the east. NEWBEAM= Beam sizes new maj, min axes (arcsec): Wanted size of major, minor axis of smoothed new beam in arcsec. For one dimensional smoothing, give one of the axes the same value as the original axis and give the new position angle the same value as the old one. NEWPOSANG= Give position angle new beam (deg): [old PA] Position angle in degrees of major axis of smoothed beam wrt. the north. ** CONBEAM= Give maj. & min. axis of con. [Calculated] beam (arcsec): Size of major and minor axis in arcsec of the gaussian convolution function. ** CONPOSANG= Give P.A. (deg) major axis (N->E): [Calculated] Position angle of major axis wrt North in the direction of East SCALE= Give scale factor for output: [Calculated] Scaling factor output subsets. Description: SMOOTH Convolves maps to larger beam sizes using a Gaussian convolution function. This function is cal- culated by giving the current and the new (wanted) beam sizes in R.A. and Dec. in arcseconds and the current and the new position angle of the beam. The position angle is given in degrees and is measured with respect to the north in the direction of the east. If this information is not available, the convolution parameters can be given by the user. The convolution function is normal- ized to unity. Note that the definition of Tb (bright- ness temperature) is not preserved, e.g. a point source at a certain point of X mJy does not contain the value X at that point after smoothing. To maintain the same definition in old and new (smoothed) subsets the latter can be scaled using the keyword SCALE= The appropriate scale factors may be determined empirically by using SMOOTH on an antenna pattern (AP) first, and determining the factor needed to scale the central value back to unity. To facilitate this procedure, SMOOTH can be used in an automatic mode. Since the original beam usually is not gaussian, the assumption of its being so leads to a new beam somewhat different from the one specified. In the automatic mode first only the appropriate AP is given, and the wanted new beam. SMOOTH then performs several iterations, during each one of which the AP is smoothed, whereby the beam size of the resulting AP converges to the user given wanted value. Once the convergence has proceeded far enough the currently valid smoothing para- meters are preserved, and the appropriate scaling is determined. With the keywords FITBOX= and CLIP= the user can modify the default box used in the fit. Hereafter the program proceeds with smoothing the set, and if selected, the AP itself. Output for the AP is specified with the keyword OUTAPSET= In automatic mode SMOOTH updates the new set header with the destination of the AP associated with the output. If output for a smoothed AP is selected, the name of the input AP will be written in its header. In non-automatic mode the AP information is removed. Whenever the smoothing routine encounters a blank value within the smoothing beam, it sets the smoothed pixel value to blank. This results in a growth of blanks in your subset. To avoid this problem, make sure the subsets don't contain any blanks. In non-automatic mode, the parameters of the convolution function can be a direct input also. This is done by specifying the (hidden) keywords CONBEAM= and CONPOSANG=. Use dummy values for the other keywords (OLDBEAM=, NEWBEAM=) that are prompted. The default value for SCALE= is obtained by convolving the calculated convolution function with a 2-d gaussian with maximum amplitude equal to 1 and with parameters given in OLDBEAM= and OLDPOSANG= The result is a gaussian of which the central value is not longer equal to zero. The scale factor is the number that is needed to scale the central value back to 1. Notes: There is a limit using large beams. If you want to smooth with a large beam, it is best to smooth to an intermediate sized beam first. If you set the output mode to TEST, you get the presmooth iteration results in your log-file. Updates: May 10, 1990: VOG, Document created Jun 27, 1991: VOG, Presmooth iteration rewritten Aug 26, 1992: VOG, All rotation related routines have angle offset wrt pos. X-axis Dec 5, 1996: VOG, Changed defaults for OLDBEAM= in non automatic mode Aug 5, 2008: JPT, Removed redundant write statement