MODMAP


MODMAP  creates  a  map  file  (FITS  image)  from  a  model  file  by
convolution  with  a  Gaussian  beam.   The  map file may be copied to
FITS-format tape for transport  to  other  institutions,  passed  into
AIPS, or displayed using programs MAPPLOT and MAPDISP.


Example:

$ MODMAP
  MODFILE    = "double.mod"
  MAPFILE    = "test.map"
  LRTB       = -10, 10, 10, -10
  XYINT      = 0.2
  BEAM       = 1.5
  FREQ       = 5000
  SOURCE     = "Double Model"
  DATE-OBS   = "02/12/84"
/
$ 


Parameters:

Parameter names (except DATE-OBS) may be  abbreviated  to  uniqueness.
End   the   list  of  parameters  with  a  slash  (/)  or  end-of-file
(control-Z).

MODFILE = "filename"  :   name  of  the  input  model  file  (must  be
          specified).

MAPFILE = "filename" :  name for the output FITS-format map file (must
          be specified).

BITPIX = n :  specifies the BITPIX parameter for the  FITS-format  map
          file  which  controls whether pixels are stored as 16-bit or
          32-bit integers.  Possible values are 16 and 32; the default
          is 16.  BITPIX=16 allows a "dynamic range" of about 32000:1.
          BITPIX=32 allows a much greater dynamic range but uses  more
          disk space.

LRTB = x1, x2, y1, y2 :  specifies the location of the  edges  of  the
          map  in  milliarcseconds relative to the origin (0,0) of the
          model.  Note that x1 < x2, y1 > y2.

XYINT =  x  :   specifies  the  cellsize  (sampling)  of  the  map  in
          milliarcsec.   Choose  XYINT  to adequately sample the beam.
          The number of pixels in the output map will be (x2-x1)/xyint
          +  1  in  the  x  direction  and  (y1-y2)/xyint + 1 in the y
          direction.

ROTATE = angle :  specifies an angle through which to rotate the model
          before  creating  the  map.   Use  of  this  option  is  not

MODMAP                                                            Page 2


          recommended.

BEAM = bmaj, bmin, bpa :  specifies the parameters of  the  convolving
          Gaussian  beam.  bmaj and bmin are the FWHM of the major and
          minor axes, respectively, in mas, and bpa  is  the  position
          angle  on the sky of the major axis in degrees.  If bmin and
          bpa are omitted, a circular beam of FWHM bmaj is used.

FREQUENCY = f :  specifies  the  observing  frequency  in  MHz  to  be
          recorded in the FITS image header.

SOURCE = "Name" :  specifies an object name to be recorded in the FITS
          image header (FITS parameter "OBJECT").

NUMBER = n  :   if  NUMBER  is  specified,  only  the  first  n  model
          components will be used in calculating the map.

TELESCOP = "text" :  use this parameter to  supply  a  value  for  the
          "TELESCOP"  (name  of telescope) parameter in the FITS image
          header.  Any character string up to  16  characters  can  be
          used,  but  some  FITS  readers may truncate the string to 8
          characters.  For VLBI experiments, the usual  convention  is
          to  use  the one-letter abbreviations of the antennas, e.g.,
          TELESCOP="BKGYO".  (If you do not provide this parameter, no
          TELESCOP entry will be made in the FITS header.)

DATE-OBS = "text" :  use this parameter to  supply  a  value  for  the
          "DATE-OBS" (date of observation) parameter in the FITS image
          header.  The normal FITS convention for dates should be used
          (dd/mm/yy),  e.g.,  DATE-OBS="21/04/86"; but MODMAP does not
          enforce this convention and allows you to supply any  string
          of  up  to  16  characters.   (If  you  do  not provide this
          parameter, no DATE-OBS  entry  will  be  made  in  the  FITS
          header.)


Limitations:

Maximum number of model components = 10000.
Maximum number of map pixels = 262144 (e.g.  512x512, 1024x256).
Only Gaussian and delta-function model components are allowed.


Program History:

Version 1.0:  1983 Aug 29 - new program (TJP).
Version  1.1:   1984  Jan  20  -  use  new   FITS   routines;   remove
          FORMAT="MODPLOT" option (TJP).
Version 1.2:  1986 Oct 31  -  add  TELESCOP  and  DATE-OBS  parameters
          (Tasso Tzioumis).