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CMSYSTIME

CMSYSTIME

Name


  CMSYSTIME

Author


  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
  craigm@lheamail.gsfc.nasa.gov

Purpose


  Compute seconds since Jan 1, 1970 and (Modified) Julian Days

Calling Sequence


  TIMEVAL1 = CMSYSTIME(TIMEVAL0, ...)

Description



  CMSYSTIME serves two functions. It computes the current time in a
  fashion similar to the built-in IDL system function SYSTIME(). It
  also can convert between various time representations and systems,
  including a textual format.
  The current time can be obtained by invoking CMSYSTIME with the
  /NOW keyword (which is entirely equivalent to SYSTIME(1)).
  The most substantial part of CMSYSTIME, which distinguishes it
  from SYSTIME, is its ability to convert between different time
  formats. CMSYSTIME recognizes can recognize and convert between
  time in seconds (seconds since Jan 1, 1970 [ = SEC ]) and days
  (Julian days [ = JDAY ] or "Modified" Julian days [ = MJD = JDAY -
  2400000.5 ]). It can also recognize and convert between local and
  GM time.
  CMSYSTIME takes maximum care to preserve the full numerical
  precision of the time values. It converts all values to double
  precision and may return days and seconds with fractional parts.
  CMSYSTIME can also represent any time textually, not just the
  current time. The following textual formats are supported:
        DOW MMM DD hh:mm:ss YYYY - (Default - same as SYSTIME)
        DOW MMM DD YYYY hh:mm:ss.uuuuuu TTTTT - (/EXTENDED)
  where DOW and MMM are the abbreviated day of week and month in
  English, DD is the day of the month, YYYY is the year, hh:mm:ss is
  the time in 24 hr military time, uuuuuu are additional
  microseconds, TTTTT is the timezone offset (in +hhmm
  representation).
  CMSYSTIME accepts one parameter, the input time to be converted.
  Unlike SYSTIME, the *function* of CMSYSTIME is governed by various
  keywords, as summarized in the following table:
  Converting from Converting to
  --------------- -------------
  JDAY - /FROM_JULIAN JDAY - /JULIAN
  MJD - /FROM_MJD MJD - /MJD
  SEC - (Default) SEC - /SECONDS
  Current time - /NOW TEXT - (Default or /EXTENDED)
  Local time - /FROM_LOCAL Local time - /LOCAL
  GM time - (Default) GM time - (Default)
 
  If no argument is specified, the default is to report the current
  time textually in the GM time zone. CMSYSTIME automatically
  determines the local time zone.

Inputs



  TIMEVAL0 - input time, in seconds or days, as described above.
              This value is ignored if the NOW keyword is set. Array
              values are allowed.

Keywords



  NOW - If set, TIMEVAL0 is ignored and the current time is used as
        input.
  FROM_JULIAN - If set, TIMEVAL0 is in Julian days.
  FROM_MJD - If set, TIMEVAL0 is in Modified Julian days (MJD).
  FROM_LOCAL - If set, TIMEVAL0 is in the local time zone.
                If no FROM_ keywords are set, the input is assumed
                to be seconds from Jan 1, 1970.
  JULIAN - If set, the input is converted to Julian days upon output.
  MJD - If set, the input is converted to MJD upon output.
  SECONDS - If set, the input is converted to seconds from Jan
            1, 1970 upon output.
  LOCAL - If set, the input is converted to the local time zone.
            If no "destination" keywords are set, the output is
            converted to textual representation.
  EXTENDED - Convert to a textual representation with additional
              information, as noted above.
  TIMEZONE - Upon output, the timezone offset is returned in this
              keyword. The offset is time difference in seconds
              between GM time and the local time, such that LOCALTIME
              = GMTIME + TIMEZONE

Returns


  The resulting converted time(s), either as a double precision
  number or a string.

Example


 
  The equivalent to SYSTIME(0)
    IDL> print, systime(0) & print, cmsystime(/now, /local)
    Wed Jul 5 12:10:46 2000
    Wed Jul 5 12:10:46 2000
  The equivalent to SYSTIME(1)
    IDL> print, systime(1) & print, cmsystime(/now,/seconds)
        9.6277750e+08
        9.6277750e+08
  Comparison between local and GM time zones (I live in the Eastern
    US, daylight savings)
    IDL> print, cmsystime(/now,/extended)
    Wed Jul 5 2000 16:13:15.659000 -0400
    IDL> print, cmsystime(/now,/local,/extended)
    Wed Jul 5 2000 12:13:15.664000 -0400
   
  What day of the week was it 200 days ago? (Note, there are 86400
    seconds in one day)
    IDL> today = cmsystime(/now,/seconds)
    IDL> print, cmsystime(today-86400L*200, /local)
    Sat Dec 18 12:17:52 1999
   

See Also



  SYSTIME, JULDAY, CALDAT

Modification History


  Written, CM, 05 Jul 2000
  Printed time zone is zero when LOCAL=0, CM, 21 Aug 2000
  Corrected behavior of /MJD (Thanks to Marshall Perrin), 03 Jun
    2002
  Corrected local vs. UTC problem caused by fractional UTC seconds,
    (thanks to J. Wolfe) CM, 28 Dec 2005
  Corrected problem with Julian day arrays, (thanks to W. Landsman),
    CM, 29 Dec 2005
  $Id: cmsystime.pro,v 1.5 2005/12/29 18:07:48 craigm Exp $



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