  XCompare_Lists help page



  GENERAL DESCRIPTION

  The XCompare_Lists widget compares two lists of stars,
  resulting for instance from the analysis of two images of
  the same field observed at different wavelenghts.
  In general the two frames are translated and rotated one
  another: the proper transformation must be determined, in
  order to map one set of coordinates onto the other.
  After matching the reference frames, the common points
  can be found.
  The input lists of stars must have the same format as the
  outputs produced by XStarFinder_Run; the data must be
  stored on rows of 7 columns each, in the following order:

  x  y  flux  sigma_x  sigma_y  sigma_flux  correlation

  The reference list used to match the reference frames (see
  the 'File' menu below) must contain only the coordinates
  of the reference stars, in the following order:

  x  y



  CONTROLS/BUTTONS

  'File':
      The 'File' pull-down menu includes two sub-menus for
      lists input/output.
      The 'Load' sub-menu allows the user to read
      - the lists to compare, named List 1 and List 2;
      - a reference list (coordinates only!), containing a subset
        of the objects in List 1, which is used to find the
        coordinate transformation between the two reference frames.
      The 'Save' sub-menu allows the user to save the processed
      Lists 1 and 2, either after matching the reference frames
      or after finding the common objects.
 
  'Match coordinates':
      Find the optimal transformation to map coordinates of
      List 2 onto the reference frame of List 1. This is done
      by the widget application XMatch_Coord.

  'Find coincident':
      Find coincident points in the two lists. The user is
      requested to supply a 'matching distance', which
      represents a tolerance to identify coincident points.

  'Color Magnitude Diagram':
      Create a simple color-magnitude diagram, plotting Mag1
      on the vertical axis vs. (Mag1 - Mag2) on the horizontal
      axis, where Mag1 and Mag2 are the magnitudes of the
      stars in Lists 1 and 2 respectively. Magnitudes are
      defined as
      Mag = -2.5 * Log10(Flux);
      the user is requested to enter a zero-point for the
      magnitude scale.
      The plot is created by means of the XPlot widget
      application and can be saved as a PostScript file.

  'Help':
      Display this help page.

  'Exit':
      Quit XCompare_Lists.