NAME:
  tnorecov
 PURPOSE:
  Real-time planning and field selection tool for TNO survey observations.
 DESCRIPTION:
  This is a non-blocking widget tool.  It expects to read a file with
    a list of object coordinates and other information.  The name of the
    file is not arbitrary.  The root of the file name must be a 6-digit
    encoding of the time for which the positions in the file are calculated
    for.  YYMMDD (year, month, day) is thus required and the time is assumed
    to be 0h UT on that day.  The suffix of the file name is normally '.dat',
    but this is not a requirement but rather the initial value for the file
    filter.
  Files of the proper format are generated for each day on that day and can
    be found at http://www.boulder.swri.edu/~buie/kbo/recov.  The files in this
    area are somewhat self-explanatory.  You can load the file of interest
    using the "Open" option under the "File" menu.

   There is a second file that is written as you tag fields with their
     observation date and time.  This file is named YYMMDD.tim (same root as
     the positions file that was read at the start) and is
     written to the directory where you were when you started the program.
     This file records the start times of the two visits to the field.
     You must provide the y/m/d as well as h:m:s in the time field.  Here
     are a few example lines from observed fields:

2060 2000/07/28_23:48:45 2000/07/29_02:38:50
20000 2000/07/28_23:41:58 2000/07/29_02:33:09
95FB21 2000/07/28_23:33:50
00CR105 2000/07/28_23:55:46 2000/07/29_02:45:07

   If a field is not present, it hasn't yet been observed.  If a field has
     only been observed once you'll only see one time (like 95FB21 above).

   Because the tool is non-blocking, you can continue to use IDL normally
     from the command line while this tool is running.  But, only one
     copy of this tool is permitted at any given time.

 CATEGORY:
  Astronomy

 CALLING SEQUENCE:
  tnorecov

 INPUTS:

 OPTIONAL INPUT PARAMETERS:

 KEYWORD INPUT PARAMETERS:

  AMCRIT  - Airmass limit, default=2.5

  DB      - Name of database for extra information.  This is expected to
                be the DES database in structure and content.  Default is
                to not look to any database.

  DT      - Offset from true time in hours (default=0), this is used
               mostly for testing.

  MIN1YERR - This sets the threshold of interesting objects as defined by
               their error 1 year into the future.  Any object with a total
               error less than this threshold will not appear as a candidate
               for observation.  The default is 20 arcsec.  If you wish to
               turn this feature off set MIN1YERR to 0.

  OBSFILE - Name (including path) of the file containing the observatory
              code information.  Default is obscode.dat and must reside
              in your IDL_PATH.  This file is included in my library so
              you normally don't need to worry about this.

  OBSCODE - Observatory id code, default is '688' (Lowell Observatory)

 OUTPUTS:

 KEYWORD OUTPUT PARAMETERS:

 COMMON BLOCKS:

 SIDE EFFECTS:

 RESTRICTIONS:
  Only one instance at a time is allowed.

 PROCEDURE:

 MODIFICATION HISTORY:
  Written by Marc W. Buie, Lowell Observatory, 2000/07/30
  2001/03/12, MWB, numerous changes including online help files.
  2001/03/14, MWB, changed for new format of support file.
  2001/06/09, MWB, object coordinates updated for changing time.  Make the
                 widget independent of the working directory of the main IDL
                 window.
  2001/06/19, MWB, added Show Object Info on Tools menu item.
  2001/10/09, MWB, updated for new .[s]dat file format
  2002/03/06, MWB, added 'Find Object' tool and 'Set Date/Time' tool.
  2002/09/09, MWB, added support for string obscode values
  2004/11/14, MWB, read two new fields on .dat files (error and error+1y)
                      added MIN1YERR keyword
                      changed "find object" so that = is optional