CDF_TT2000
----------

The CDF_TT2000 procedure computes or breaks down a single or an array of
CDF_TIME_TT2000 value(s) in a CDF file. When computing an epoch, any
missing value is considered to be zero. 

If you supply a scalar or an array values for the TT2000 argument and set
the BREAKDOWN_EPOCH keyword, CDF_EPOCH will break down the epoch value(s)
into the Year, Month, Day, etc. and insert the values into the named
variables you supply. If you specify the Year (and optionally, the Month, 
Day, etc.) in a scalar or array and set the COMPUTE_EPOCH keyword, 
CDF_EPOCH will compute the epoch and place the value(s) in the named 
variable supplied as the Epoch parameter. 

Note:
  You must set either the BREAKDOWN_EPOCH or COMPUTE_EPOCH keyword. 


Syntax 
  CDF_TT2000, Epoch, Year, Month, Day [, Hour, Minute, Second, Milli,
        Micro, Nano] [, /BREAKDOWN_EPOCH] [, /COMPUTE_EPOCH] [, /TOINTEGER] 

Arguments 
  Epoch    A scalar or an array (<= 2D) of Epoch value(s) to be broken down,
           or a named variable into which the computed epoch will be placed.
           A TT2000 Epoch value is the number of nanoseconds since J2000
           (2000-01-01T12:00:00.000000000) with leap seconds included. 

    Note:
      CDF_TIME_TT2000 is based on J2000.
      It can only cover +/- 272 years from J2000.  To convert CDF TT2000
      epochs into date/times and vice versa, you should only use the 
      CDF_TT2000 routine with either the BREAKDOWN_EPOCH or COMPUTE_EPOCH 
      keyword. 

  Year     The year(s) (such as 1992) or a named variable. 

  Month    The month(s) (1-12) or a named variable. You can also set the Month 
           argument equal to zero, in which case the Day argument can take 
           on any value between 1-366; this number is interpreted as the 
           "Day of the Year" rather than a "Day of the Month". 

  Day      The day(s) (1-31) or a named variable. If the Month argument is set 
           equal to zero, Day can be set to any value between 1-366. 

  Hour     The hour(s) (0-23) or a named variable. 

  Minute   The minute(s) (0-59) or a named variable. 

  Second   The second(s) (0-59 or 0-60 if leap second) or a named variable. 

  Milli    The millisecond(s) (0-999) or a named variable. 

  Micro    The microsecond(s) (0-999) or a named variable. 

  Nano     The nanosecond(s) (0-999) or a named variable. 

  Note: For the entered date/time components to compute the epoch, only
        the last component is allowed to be fractional. Otherwise, a message of
        illegal value is returned. When an epoch is broken down into date/time
        components, all are in double form by default.   

Keywords 
  BREAKDOWN_EPOCH     
     If this keyword is set, Epoch is a value which will broken down and the 
     resulting Year, Month, Day, etc. are returned in the remaining parameters 
     which must be named variables. 

  COMPUTE_EPOCH 
     If this keyword is set, Epoch is a named variable into which the epoch 
     is placed and the other parameters are values which will be used to 
     compute the epoch. 

  TOINTEGER
     This keyword is applicable when an epoch value(s) is broken down to 
     date/time components (with BREAKDOWN_EPOCH keyword). If this keyword is
     set, all components will be in integer, instead of their default of
     doubles. 

Examples 
  To compute a single epoch value of September 20, 2005 at 3:05:46.27.02.156: 

      CDF_TT2000, epoch, 2005, 9, 20, 3, 5, 46, 27, 2, 156, /COMPUTE_EPOCH 

  To break down the given epoch value into standard date components: 

      CDF_TT2000, epoch, yr, mo, dy, hr, min, sec, milli, micro, nano, /BREAK 

  To compute an array of epoch values from the following three dates:
  20-Sep-2005 03:05:46:156.111.222,
  20-Sep-2005 03:06:22:234.333.444,
  20-Sep-2005 03:07:12:345.555.666:   
      
      yy = [2005, 2005, 2005]
      mm = [9,       9,    9]
      dd = [20,     20,   20]
      hh = [3,       3,    3]
      mn = [5,       6,    7]
      ss = [46,     22,   12]
      ms = [156,   234,  345]
      us = [111,   333,  555]
      ns = [222,   444,  666]
      CDF_TT2000, epoch2, yy, mm, dd, hh, mn, ss, ms, us, ns, /COMPUTE_EPOCH

  Since the year, month, day, hour fields are the same in this sample, 
  alternatively, the above command can be written as:

      CDF_TT2000, epoch2, 2005, 9, 20, 3, mn, ss, ms, us, ns, /COMPUTE_EPOCH 

  To break down the above vectorized epoch values into standard date
  components: 

      CDF_TT2000, epoch2, yr, mo, dy, hr, min, sec, milli, micro, nano, /BREAK 

  All yr, mo, dy, hr, min, sec, milli, micro, nano fields will be in array form.

Version History 
  Introduced: CDF 3.4.0

See Also
  CDF_ENCODE_TT2000, CDF_PARSE_TT2000