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Index Page str2et_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       str2et_c ( String to ET )

       void str2et_c ( ConstSpiceChar * timstr,
                       SpiceDouble    * et   )

#### Abstract

       Convert a string representing an epoch to a double precision
       value representing the number of TDB seconds past the J2000
       epoch corresponding to the input epoch.

#### Required_Reading

       TIME

#### Keywords

       TIME

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       timstr     I   A string representing an epoch.
       et         O   The equivalent value in seconds past J2000, TDB.

#### Detailed_Input

       timstr      is a string representing an epoch. Virtually all
                   common calendar representations are allowed. You may
                   specify a time string belonging to any of the
                   systems TDB, TDT, UTC. Moreover, you may specify a
                   time string relative to a specific UTC based time
                   zone.

                   The rules used in the parsing of `timstr' are spelled out
                   in great detail in the reference document time.req. The
                   basics are given in the -Particulars section below.

#### Detailed_Output

       et          is the double precision number of TDB seconds past the
                   J2000 epoch that corresponds to the input `timstr'.

#### Parameters

       None.

#### Exceptions

       1)  If the `timstr' input string cannot be recognized as a
           legitimate time string, the error SPICE(UNPARSEDTIME) is
           signaled by a routine in the call tree of this routine.

       2)  If more than one time system is specified as part of the input
           time string, the error SPICE(TIMECONFLICT) is signaled by a
           routine in the call tree of this routine.

       3)  If any component of the input time string is outside the
           normal range of usage, the error SPICE(BADTIMESTRING) is
           signaled by a routine in the call tree of this routine. For
           example, the day January 35 is outside the normal range of
           days in January. The checks applied are spelled out in the
           routine TCHECK.

       4)  If a time zone is specified with hours or minutes components
           that are outside of the normal range, the error
           SPICE(TIMEZONEERROR) is signaled by a routine in the call tree
           of this routine.

       5)  If the `timstr' input string pointer is null, the error
           SPICE(NULLPOINTER) is signaled.

       6)  If the `timstr' input string has zero length, the error
           SPICE(EMPTYSTRING) is signaled.

#### Files

       None.

#### Particulars

       This routine computes the ephemeris epoch corresponding to an
       input string. The ephemeris epoch is represented as seconds
       past the J2000 epoch in the time system known as Barycentric
       Dynamical Time (TDB). This time system is also referred to as
       Ephemeris Time (ET) throughout the SPICE Toolkit.

       The variety of ways people have developed for representing
       times is enormous. It is unlikely that any single routine
       can accommodate the wide variety of custom time formats that
       have arisen in various computing contexts. However, we
       believe that this routine will correctly interpret most time
       formats used throughout the planetary science community.
       For example this routine supports ISO time formats and UNIX
       `date` output formats. One obvious omission from the strings
       recognized by this routine are strings of the form

            93234.1829  or 1993234.1829

       Some readers may recognize this as the epoch that is 0.1829
       days past the beginning of the 234'th day of 1993. However,
       many other readers may regard this interpretation as a bit
       obscure.

       Below we outline some of the rules used in the interpretation
       of strings. A more complete discussion of the interpretation
       of strings is given in the reference document time.req.

       Default Behavior
       ----------------

       Consider the string

          1988 June 13, 3:29:48

       There is nothing in this string to indicate what time system
       the date and time belong to. Moreover, there is nothing to
       indicate whether the time is based on a 24-hour clock or
       twelve hour clock.

       In the absence of such indicators, the default interpretation
       of this string is to regard the time of day to be a time on
       a 24-hour clock in the UTC time system. The date is a date
       on the Gregorian Calendar (this is the calendar used in nearly
       all western societies).

       Labels
       ------

       If you add more information to the string, str2et_c can make a
       more informed interpretation of the time string. For example:

          1988 June 13, 3:29:48 P.M.

       is still regarded as a UTC epoch. However, with the addition
       of the "P.M." label it is now interpreted as the same epoch
       as the unlabeled epoch 1988 June 13, 15:29:48. Similarly

          1988 June 13, 12:29:48 A.M.

       is interpreted as

          1988 June 13, 00:29:48

       For the record: 12:00 A.M. corresponds to Midnight (00:00 on the
       24 hour clock.  12:00 P.M. corresponds to Noon. (12:00) on the
       24 hour clock.

       You may add still further indicators to the string. For example

          1988 June 13, 3:29:48 P.M. PST

       is interpreted as an epoch in the Pacific Standard Time system.
       This is equivalent to

          1988 June 13, 07:29:48 UTC

       The following U.S. time zones are recognized.

          EST   --- Eastern Standard Time  ( UTC-5:00 )
          CST   --- Central Standard Time  ( UTC-6:00 )
          MST   --- Mountain Standard Time ( UTC-7:00 )
          PST   --- Pacific Standard Time  ( UTC-8:00 )

          EDT   --- Eastern Daylight Time  ( UTC-4:00 )
          CDT   --- Central Daylight Time  ( UTC-5:00 )
          MDT   --- Mountain Daylight Time ( UTC-6:00 )
          PDT   --- Pacific Daylight Time  ( UTC-7:00 )

       In addition any other time zone may be specified by representing
       its offset from UTC. This notation starts with the letters "UTC"
       followed by a "+" for time zones east of Greenwich and "-" for
       time zones west of Greenwich. This is followed by the number of
       hours to add or subtract from UTC. This is optionally followed
       by a colon ":" and the number of minutes to add or subtract to
       get the local time zone. Thus to specify the time zone of
       Calcutta (which is 5 and 1/2 hours ahead of UTC) you would
       specify the time zone to be UTC+5:30. To specify the time zone
       of Newfoundland (which is 3 and 1/2 hours behind UTC) use the
       offset notation UTC-3:30.

       For the Record:  Leapseconds occur at the same time in all
       time zones. In other words, the seconds component of a time
       string is the same for any time zone as is the seconds
       component of UTC. Thus the following are all legitimate
       ways to represent an epoch of some event that occurred
       in the leapsecond

          1995 December 31  23:59:60.5  (UTC)

          1996 January   1, 05:29:60.5  (UTC+5:30 --- Calcutta Time)
          1995 December 31, 20:29:60.5  (UTC-3:30 --- Newfoundland)
          1995 December 31  18:59:60.5  (EST)
          1995 December 31  17:59:60.5  (CST)
          1995 December 31  16:59:60.5  (MST)
          1995 December 31  15:59:60.5  (PST)

       In addition to specifying time zones, you may specify that the
       string be interpreted as a formal calendar representation in
       either the Barycentric Dynamical Time system (TDB) or the
       Terrestrial Dynamical Time system (TDT).  In These systems there
       are no leapseconds. Times in TDB are written as

          1988 June 13, 12:29:48 TDB

       TDT times are written as:

          1988 June 13, 12:29:48 TDT

       Finally, you may explicitly state that the time system is UTC

          1988 June 13, 12:29:48 UTC.

       Abbreviating Years
       ------------------

       Although it can lead to confusion, many people are in the
       habit of abbreviating years when they write them in dates.
       For example

          99 Jan 13,  12:28:24

       Upon seeing such a string, most of us would regard this
       as being 1999 January 13, 12:28:24 and not January 13 of
       the year 99. This routine interprets years that are less
       than 100 as belonging either to the 1900's or 2000's. Years
       greater than 68 ( 69 - 99 ) are regarded as being an
       abbreviation with the "19" suppressed (1969 - 1999). Years
       smaller than 69 ( 00 - 68 ) are regarded as being an
       abbreviation with the "20" suppressed (2000 - 2068).

       Note that in general it is usually a good idea to write
       out the year. Or if you'd like to save some typing
       abbreviate 1999 as '99.

       If you need to specify an epoch whose year
       is less than 1000, we recommend that you specify the era
       along with the year. For example if you want to specify
       the year 13 A.D. write it as

          13 A.D. Jan 12

       When specifying the era it should immediately follow the year.
       Both the A.D. and B.C. eras are supported.

       Changing Default Behavior
       -------------------------

       As discussed above, if a string is unlabeled, it is regarded
       as representing a string in the UTC time system on the
       Gregorian calendar. In addition abbreviated years are
       regarded as abbreviations of the years from 1969 to 2068.

       You may modify these defaults through the routines timdef_c
       and tsetyr_c.

       You may:

          Set the calendar to be Gregorian, Julian or a mixture of
          two via the timdef_c;

          Set the time system to be UTC, TDB, TDT or any time zone
          via the routine timdef_c;

          Set the range of year abbreviations to be any 100 year
          interval via the routine tsetyr_c.

       See the SPICELIB routine TEXPYR and timdef_c for details on changing
       defaults.

       These alterations affect only the interpretation of unlabeled
       strings. If an input string is labeled the specification
       in the label is used.

       If any component of a date or time is out of range, str2et_c
       regards the string as erroneous. Below is a list of
       erroneous strings and why they are regarded as such.

          1997 Jan 32 12:29:29     --- there are only 31 days in January

          '98 Jan 12 13:29:29 A.M. --- Hours must be between 1 and 12
                                       inclusive when A.M. or P.M. is
                                       specified.

          1997 Feb 29, 12:29:20.0  --- February has only 29 days in
                                       1997. This would be ok if the
                                       year was 1996.

          1992 Mar 12 12:62:20     --- Minutes must be between 0 and 59
                                       inclusive.

          1993 Mar 18 15:29:60.5   --- Seconds is out of range for this
                                       date. It would not be out of
                                       range for Dec 31 23:59:60.5 or
                                       Jun 30 23:59:60.5 because these
                                       can be leapseconds (UTC).

       Specifics On Interpretation of the Input String
       -----------------------------------------------

       The process of examining the string to determine its meaning is
       called "parsing" the string. The string is parsed by first
       determining its recognizable substrings (integers, punctuation
       marks, names of months, names of weekdays, time systems, time
       zones, etc.) These recognizable substrings are called the tokens
       of the input string. The meaning of some tokens are immediately
       determined. For example named months, weekdays, time systems have
       clear meanings. However, the meanings of numeric components must
       be deciphered from their magnitudes and location in the string
       relative to the immediately recognized components of the input
       string.

       To determine the meaning of the numeric tokens in the input
       string, a set of "production rules" and transformations are
       applied to the full set of tokens in the string. These
       transformations are repeated until the meaning of every token
       has been determined, or until further transformations yield
       no new clues into the meaning of the numeric tokens.

       1)  Unless the substring "JD" or "jd" is present, the string is
           assumed to be a calendar format (day-month-year or year and
           day of year). If the substring JD or jd is present, the
           string is assumed to represent a Julian date.

       2)  If the Julian date specifier is not present, any integer
           greater than 999 is regarded as being a year specification.

       3)  A dash "-" can represent a minus sign only if it precedes
           the first digit in the string and the string contains
           the Julian date specifier (JD). (No negative years,
           months, days, etc. are allowed).

       4)  Numeric components of a time string must be separated
           by a character that is not a digit or decimal point.
           Only one decimal component is allowed. For example
           1994219.12819 is sometimes interpreted as the
           219th day of 1994 + 0.12819 days. str2et_c does not
           support such strings.

       5)  No exponential components are allowed. For example you
           can't specify the Julian date of J2000 as 2.451545E6.
           You also can't input 1993 Jun 23 23:00:01.202E-4 and have
           to explicitly list all zeros that follow the decimal
           point: i.e. 1993 Jun 23 23:00:00.0001202.

       6)  The single colon (:) when used to separate numeric
           components of a string is interpreted as separating
           Hours, Minutes, and Seconds of time.

       7)  If a double slash (//) or double colon (::) follows
           a pair of integers, those integers are assumed  to
           represent the year and day of year.

       8)  A quote followed by an integer less than 100 is regarded
           as an abbreviated year. For example: '93 would be regarded
           as the 93rd year of the reference century. See the SPICELIB
           routine TEXPYR for further discussion of abbreviated years.

       9)  An integer followed by "B.C." or "A.D." is regarded as
           a year in the era associated with that abbreviation.

       10  All dates are regarded as belonging to the extended
           Gregorian Calendar (the Gregorian calendar is the calendar
           currently used by western society). See the routine timdef_c
           to modify this behavior.

       11) If the ISO date-time separator (T) is present in the string
           ISO allowed token patterns are examined for a match
           with the current token list. If no match is found the
           search is abandoned and appropriate diagnostic messages
           are generated. Historically the interpretation of ISO
           formatted time strings deviates from the ISO standard in
           allowing two digit years and expanding years in the 0 to 99
           range the same way as is done for non ISO formatted strings.
           Due to this interpretation it is impossible to specify
           times in years in the 0 A.D. to 99 A.D. range using ISO
           formatted strings on the input.

       12) If two delimiters are found in succession in the time
           string, the time string is diagnosed as an erroneous string.
           (Delimiters are comma, white space, dash, slash, period, or
           day of year mark. The day of year mark is a pair of forward
           slashes or a pair of colons.)

           Note the delimiters do not have to be the same. The pair
           of characters ",-" counts as two successive delimiters.

       13) White space and commas serve only to delimit tokens in the
           input string. They do not affect the meaning of any
           of the tokens.

       14) If an integer is greater than 1000 (and the "JD" label
           is not present, the integer is regarded as a year.

       15) When the size of the integer components does not clearly
           specify a year the following patterns are assumed

           Calendar Format

              Year Month Day
              Month Day Year
              Year Day Month

              where Month is the name of a month, not its numeric
              value.

              When integer components are separated by slashes (/)
              as in 3/4/5. Month, Day, Year is assumed (2005 March 4)

           Day of Year Format.

              If a day of year marker is present (// or ::) the
              pattern

                I-I// or I-I:: (where I stands for an integer)

              is interpreted as Year Day-of-Year. However, I-I/ is
              regarded as ambiguous.

#### Examples

       The numerical results shown for these examples may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) Suppose you would like to determine whether your favorite
          time representation is supported by str2et_c. The small
          program below gives you a simple way to experiment with
          str2et_c. (Note that erroneous inputs will be flagged by
          signaling an error.)

          Example code begins here.

          /.
             Program str2et_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main()
          {

             /.
             Local constants
             ./
             #define FILSIZ          128
             #define TIMSIZ           64

             /.
             Local variables
             ./
             SpiceChar               caldr  [ TIMSIZ ];
             SpiceChar               dayofy [ TIMSIZ ];
             SpiceChar               lsk    [ FILSIZ ];
             SpiceChar               timstr [ TIMSIZ ];

             SpiceDouble             et;

             /.
             First get the name of the leapseconds kernel, and load it.
             ./
             prompt_c ( "Leapseconds kernel: ", FILSIZ, lsk );
             furnsh_c ( lsk );

             /.
             Get the time string.
             ./
             prompt_c ( "Time string: ", TIMSIZ, timstr );

             /.
             Convert the string to ET and then back to UTC calendar
             and day-of-year formats.
             ./
             str2et_c ( timstr, &et );
             et2utc_c ( et, "C", 0, TIMSIZ, caldr  );
             et2utc_c ( et, "D", 0, TIMSIZ, dayofy );

             /.
             Print the results
             ./
             printf ( "\n" );
             printf ( "TBD seconds from J2000 epoch: %f\n", et     );
             printf ( "Calendar    Format:           %s\n", caldr  );
             printf ( "Day of year Format:           %s\n", dayofy );

             return ( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, using the LCK file named naif0012.tls and the time
          string "2017-07-14T19:46:00", the output was:

          Leapseconds kernel: naif0012.tls
          Time string: 2017-07-14T19:46:00

          TBD seconds from J2000 epoch: 553333629.183727
          Calendar    Format:           2017 JUL 14 19:46:00
          Day of year Format:           2017-195 // 19:46:00

       2) Below is a sampling of some of the time formats that are
          acceptable as inputs to str2et_c. A complete discussion of
          permissible formats is given in the reference document
          time.req.

          ISO (T) Formats.

          String                        Year Mon  DOY DOM  HR Min Sec
          ----------------------------  ---- ---  --- ---  -- --- ------
          1996-12-18T12:28:28           1996 Dec   na  18  12  28 28
          1986-01-18T12                 1986 Jan   na  18  12  00 00
          1986-01-18T12:19              1986 Jan   na  18  12  19 00
          1986-01-18T12:19:52.18        1986 Jan   na  18  12  19 52.18
          1986-01-18T12:19:52.18Z       1986 Jan   na  18  12  19 52.18
          1995-08T18:28:12              1995  na  008  na  18  28 12
          1995-08T18:28:12Z             1995  na  008  na  18  28 12
          1995-18T                      1995  na  018  na  00  00 00
          0000-01-01T                   1 BC Jan   na  01  00  00 00

          Calendar Formats.

          String                        Year   Mon DOM  HR Min  Sec
          ----------------------------  ----   --- ---  -- ---  ------
          Tue Aug  6 11:10:57  1996     1996   Aug  06  11  10  57
          1 DEC 1997 12:28:29.192       1997   Dec  01  12  28  29.192
          2/3/1996 17:18:12.002         1996   Feb  03  17  18  12.002
          Mar 2 12:18:17.287 1993       1993   Mar  02  12  18  17.287
          1992 11:18:28  3 Jul          1992   Jul  03  11  18  28
          June 12, 1989 01:21           1989   Jun  12  01  21  00
          1978/3/12 23:28:59.29         1978   Mar  12  23  28  59.29
          17JUN1982 18:28:28            1982   Jun  17  18  28  28
          13:28:28.128 1992 27 Jun      1992   Jun  27  13  28  28.128
          1972 27 jun 12:29             1972   Jun  27  12  29  00
          '93 Jan 23 12:29:47.289       1993*  Jan  23  12  29  47.289
          27 Jan 3, 19:12:28.182        2027*  Jan  03  19  12  28.182
          23 A.D. APR 4, 18:28:29.29    0023** Apr  04  18  28  29.29
          18 B.C. Jun 3, 12:29:28.291   -017** Jun  03  12  29  28.291
          29 Jun  30 12:29:29.298       2029+  Jun  30  12  29  29.298
          29 Jun '30 12:29:29.298       2030*  Jun  29  12  29  29.298

          Day of Year Formats.

          String                        Year  DOY HR Min Sec
          ----------------------------  ----  --- -- --- ------
          1997-162::12:18:28.827        1997  162 12  18 28.827
          162-1996/12:28:28.287         1996  162 12  28 28.287
          1993-321/12:28:28.287         1993  231 12  28 28.287
          1992 183// 12:18:19           1992  183 12  18 19
          17:28:01.287 1992-272//       1992  272 17  28 01.287
          17:28:01.282 272-1994//       1994  272 17  28 01.282
          '92-271/ 12:28:30.291         1992* 271 12  28 30.291
          92-182/ 18:28:28.281          1992* 182 18  28 28.281
          182-92/ 12:29:29.192          0182+ 092 12  29 29.192
          182-'92/ 12:28:29.182         1992  182 12  28 29.182

          Julian Date Strings

          jd 28272.291                  Julian Date   28272.291
          2451515.2981 (JD)             Julian Date 2451515.2981
          2451515.2981 JD               Julian Date 2451515.2981

                                        Abbreviations Used in Tables

                                          na    --- Not Applicable
                                          Mon   --- Month
                                          DOY   --- Day of Year
                                          DOM   --- Day of Month
                                          Wkday --- Weekday
                                          Hr    --- Hour
                                          Min   --- Minutes
                                          Sec   --- Seconds

          *  The default interpretation of a year that has been
             abbreviated to two digits with or without a leading quote
             as in 'xy or xy (such as '92 or 92) is to treat the year as
             19xy if xy > 68 and to treat it as 20xy otherwise. Thus '70
             is interpreted as 1970 and '67 is treated as 2067. However,
             you may change the "split point" and centuries through use
             of the CSPICE routine tsetyr_c. See that routine for a
             discussion of how you may reset the split point.

          ** All epochs are regarded as belonging to the Gregorian
             calendar. We formally extend the Gregorian calendar backward
             and forward in time for all epochs. If you have epochs
             belonging to the Julian Calendar, consult the SPICELIB
             routines TPARTV and JUL2GR for a discussion concerning
             conversions to the Gregorian calendar and ET. The routines
             timdef_c and str2et_c, used together, also support conversions
             from Julian Calendar epochs to ET.

          +  When a day of year format or calendar format string is
             input and neither of the integer components of the date is
             greater than 1000, the first integer is regarded as being
             the year.

          Any integer greater than 1000 is regarded as a year
          specification. Thus 1001-1821//12:28:28 is interpreted as
          specifying two years and will be rejected as ambiguous.

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       C.H. Acton          (JPL)
       N.J. Bachman        (JPL)
       M. Costa Sitja      (JPL)
       J. Diaz del Rio     (ODC Space)
       W.L. Taber          (JPL)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 1.2.0, 23-DEC-2021 (JDR) (EDW) (MCS)

           Changed input argument name "str" to "timstr" for consistency
           with other routines.

           Header edits to expand description of ISO format.

           Edited the header comments to comply with NAIF standard.
           Updated code example.

           Comments concerning the default century for abbreviated years
           were updated to reflect changes to texpyr_.

           Replaced references to tpartv_ by time.req.

       -CSPICE Version 1.1.5, 02-NOV-2009 (CHA)

           A few minor grammar fixes in the header.

       -CSPICE Version 1.1.4, 16-JAN-2008 (EDW)

           Corrected typos in header titles:

           Detailed Input to -Detailed_Input.
           Detailed Output to -Detailed_Output.

       -CSPICE Version 1.1.3, 12-NOV-2006 (EDW)

           Added -Parameters section header.

       -CSPICE Version 1.1.2, 29-JUL-2003 (CHA) (NJB)

           Various minor header corrections were made.

       -CSPICE Version 1.1.1, 10-FEB-2002 (NJB)

           Corrected typo in header.

       -CSPICE Version 1.1.0, 08-FEB-1998 (NJB)

           Re-implemented routine without dynamically allocated, temporary
           strings. -Exceptions section of header was updated.

       -CSPICE Version 1.0.0, 25-OCT-1997 (EDW) (WLT)

#### Index_Entries

       Convert a string to TDB seconds past the J2000 epoch

#### Link to routine str2et_c source file str2et_c.c

    Fri Dec 31 18:41:13 2021