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  This function translates dates for the SNOE S/C and mission,
  between various different formats.


  SNOE, date, time

Calling Sequence

result = SNOE_DATE( date, /from_xxx, /to_xxx )


Date: a date, in one of the formats listed below.

Keyword Parameters

      FROM_YMD: A keyword specifing that the input is a 3 element
      vector, where the first element is a four digit year between
      1998 and 2003. The second element is a month number, and the
      third element is the day-of-month. The year can be either 2 or
      4 digits
      FROM_YYDDD: A keyword specifying that the input is a number
      of the form YYDDD. 20 represents 00020, or day 20 of year 2000.
      98070 is the first day of the mission.
      FROM_YYYYDDD: A keyword specifying that the input is a number
      of the form YYYYDDD. This is a four digit year, followed by a
      3 digit day-of-year.
      FROM_MISSION: A keyword specifying that the input is in day of
      mission format, where zero (0) is the first day of the
      FROM_DOY: A keyword specifying that the input is in
      Day-Of-Year format. 1 is the first day of the year.
      FROM_TODAY: This keword makes the output the current UTC date
      converted to the format specified by the /TO_xxx keyword. An
      input argument is OPTIONAL, and will be ignored if this
      keyword is set.
      TO_DOY: A keyword specifying that the output should be the day
      of year of the input date. Note that there is no distinction
      nor way to tell what year this day-of-year belongs to. You
      must deduce this based upon the input.
      TO_YMD: A keyword specifying that the output should be a 3 element
      vector of the form [y,m,d].
      TO_YYDDD: Output is in yyddd format
      TO_YYYYDDD: Output is in yyyyddd format
      TO_MISSION: Output is in day of mission format
      TO_DOM: Same as TO_MISSION


This function returns a number representing the date specified
by the /TO_xxx keyword.

Side Effects

Hopefully none.


      Only works through the following dates:
      START: 1998070(yyyyddd), 98070(yyddd), 0(mission), [1998,03,11](ymd)
      STOP: 2003365(yyyyddd), 3365(yyddd), 2121(mission),
      Should (?) work if input is [yyyy,1,doy], and keyword from_ymd set.
      NOTE: other undocumented features/bugs may exist. For example,
      ymd input [1999,01,32], and keyword to_ymd set correctly gives the
      output as [1999,02,01]. Or, input 0 and output /TO_DOY gives 365.


The code works by translating ALL input formats (ymd, yyyyddd,
doy, etc.) to Day of Mission (or Mission Index, mi). Then, mi
is converted to the output requested by the /FROM_xxx keyword.


      print, snoe_date( [2003,12,31], /from_ymd, /to_mission )
      print, snoe_date( [98,3,11], /from_ymd, /to_yyyyddd )
      print, snoe_date( 0, /from_mission, /to_yyyyddd )
      print, snoe_date( 0, /from_mi, /to_yyd ) ; UNIQUE keywords!

Modification History

  Written by: Ken Mankoff, 2001.08.28 (2001240,1266,01240,etc.)
  09/06/01 TAF; Added the double keyword so that fractional days
                  can be handled. Only works for from_yyddd and
                  from_yyyyddd for now.
  09/09/01 KDM; Added Julian day functionality
  09/13/01 KDM; Added to_doy keyword, added print warning for
                  Julian keyword.
  09/20/01 KDM; modified to allow [y,m,d] input to have 2 digit year
  04/23/02 KDM; Commented out JULIAN functionality. Removed double
                  keyword (see 09/06/01 revision). Fixed 2 digit
                  [y,m,d] error, added comments to code. Added
                  /FROM_TODAY keyword, added /FROM_DOY keyword.
  06/24/02 KDM; Added DOM (analogous to MISSION)

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