Index Page CHRONOS User's Guide

## Table of Contents

       CHRONOS User's Guide
          Abstract
          Summary
             UTC Time Types
             ET Time Types
             SCLK Time Types
             LST Time Types
          Usage
             Usage Examples -- Mars Pathfinder
             Using CHRONOS with Calling Scripts or Aliases
          Setup File
             Setup File Examples
          Appendix 1: Aliases Mimicing MPF Time Tools
          Appendix 2: Input UTC and ET Time string formats
          Appendix 3: Output Time String Formatting Rules
          Appendix 4: Output DP Number Formatting Rules

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# CHRONOS User's Guide

Last revised on 2021 SEP 10 by M. Costa Sitja.

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## Abstract

CHRONOS is a command-line program that converts between several time systems and time formats.

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## Summary

CHRONOS is a utility program that converts time between various time systems. It supports the following time systems:

UTC
  Universal Time Coordinated; UTC is a system of time keeping that gives a name to each instant of time of the International Atomic Time system; refer to the NAIF Toolkit TIME.REQ document for more discussion regarding UTC;

ET
  Ephemeris Time; Ephemeris time is the uniform time scale represented by the independent variable in the differential equations that describe the motions of the planets, sun and moon. CHRONOS deals with one of the two forms of ET -- Barycentric Dynamical Time (TDB) which is used when describing the motion of bodies with respect to the solar system barycenter; refer to the NAIF Toolkit TIME.REQ document for more discussion regarding ET;

SCLK
  Spacecraft On-Board Clock Time; SCLK is the onboard time-keeping mechanism that triggers most spacecraft events and is the fundamental time measurement for referencing most spacecraft activities and instrument data; refer to the NAIF Toolkit SCLK.REQ document for more discussion regarding SCLK;

LST
  Local Solar Time; LST is simply a measure of angles between landing (sub-spacecraft) and sub-solar meridians on the surface of a body expressed as a "24 hour" local clock.

Within the supported time systems CHRONOS recognizes multiple time types. The types supported for each system are described below.

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### UTC Time Types

The following time types are supported for the UTC system:

SCET
  Spacecraft Event Time; SCET is the time of an event on-board a spacecraft; in CHRONOS input/output SCET can be represented by any time string acceptable in SPICE time conversion routines;

ERT
  Earth Received Time; ERT is the time of an event measured on the ground, such as the time when a signal about an event on-board of a spacecraft was received on the Earth; in CHRONOS input/output ERT can be represented by any time string acceptable in SPICE time conversion routines.

ETT
  Earth Transmit Time; ETT is the time when a signal received on-board a spacecraft, was transmitted from the Earth; in CHRONOS input/output ETT can be represented by any time string acceptable in SPICE time conversion routines.

LT
  One-way Light Time; LT is the one-way light time between the Earth center of mass and a spacecraft; LT cannot be input to the program; on output LT is always expressed as a number of seconds; note that LT is computed using only Newtonian assumptions about the propagation of light;

Note that on the input and output SCET, ERT or ETT time in the UTC system can be an Earth time zone time if corresponding modifiers are present in an input time string or output format picture. A few example further in the document demonstrate this.

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### ET Time Types

All of the above time types are supported ET time types. Also available is:

SECONDS
  Ephemeris Seconds past epoch J2000 (2000 JAN 01 12:00:00); ET seconds is the internal SPICE representation for ET.

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### SCLK Time Types

The following time types are supported for the SCLK system:

SCLK
  String Spacecraft Clock; string SCLK consists of a series of one or more fields, each containing an integer counter; a partition number preceding the first (leftmost) field counter and separated from it by a slash can be present in the string to identify which partition (interval between resets) this counter's readout belongs to; SCLK examples:

                                 3/1248531085.006
                                 1248543443
                                 1437200032:006:23

HEX
  HEX Spacecraft Clock; HEX SCLK has exactly the same format as string SCLK except that the counter fields contain HEX representations of the corresponding integer numbers; HEX examples:

                                 4A8ADDCA:48
                                 4A2A34BB
                                 2/4A8A5052.48.1A

TICKS
  Spacecraft Clock Ticks; SCLK Ticks is the internal SPICE representation for SCLK; it's a total number of ticks -- smallest increments of on-board clock -- since the clock was turned on;

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### LST Time Types

The following time types are supported for the LST system:

LST
  Local Solar Time; LST is the local solar time expressed by the number of local solar days (SOLs) from a landing date and using a "24-hour" clock readout within the current local solar day (HR:MN:SC); LST is a true local solar time and computed using positions of the Sun and the landing site from SPICE kernels specified in CHRONOS setup file; if a landing date is unknown to the program it cannot convert input LST to any other time system and can compute LST only without SOL number for the output; LST examples:

                                 SOL 12  12:00:01
                                 SOL 132 01:22:32.498
                                 SOL 2 9

LSUN
  Longitude of the Sun; LSUN (also known as "L-sub-s") is the planetocentric longitude of the sun, as seen from a specified body; LSUN is often used as a measure of the season on a body: for the northern hemisphere LSUN changes from 0 (spring) ---- +90 (summer) ---- +/-180 (autumn) ---- -90 (winter) ---- 0 (spring) and so on; geometrically LSUN is defined in the following frame: the positive Z direction is given by the instantaneous planetocentric North pole of the central body; the positive X direction is the cross product of the positive Z direction with the instantaneous orbital angular velocity vector; the positive Y direction is the cross product of Z and X.

Note that CHRONOS doesn't support any approximate local times such as computed by approximating over precomputed local midnight or noon epochs or computed using mean position of the Sun.

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## Usage

CHRONOS is a command line program. To convert time from one supported system/type to another, CHRONOS is used with the following command line options. Those shown within square brackets are optional. A vertical bar separates choices, only one of which may be used.

          % CHRONOS  -SETUP <setup file name OR kernel file name(s)>
                     -FROM <"from" time system>
                    [-FROMTYPE <"from" time type>]
                     -TO <"to" time system>
                    [-TOTYPE <"to" time type>]
                    [-FORMAT <output time format picture>]
                     -TIME <input time> | -BATCH
                    [-SC <sc ID>]
                    [-CENTER <central body ID>]
                    [-LANDINGTIME <UTC time of the landing>]
                    [-SOL1INDEX <index of the first SOL>]
                    [-NOLABEL]
                    [-TRACE]

The command line options above have the following meanings:

-SETUP
  this is used to specify a setup file name or directly list the names of the SPICE kernels to be used by CHRONOS; providing a setup file name on the command line is optional; if it's not present or is blank, CHRONOS tries to obtain it from the environment variable CHRONOS_SETUP_FILE;

-FROM
  this is used to specify the time system of the input time; specifying the "from" time system is required;

-FROMTYPE
  this is used to specify the time type of the input time; specifying "from" time type is optional; if it's not present or is blank, CHRONOS assumes the default time type for the input time system (SCET for UTC and ET, SCLK for SCLK, and LST for LST);

-TO
  this is used to specify the time system of the output time; specifying the "to" time system is required;

-TOTYPE
  this is used to specify the time type of the output time; specifying "to" time type is optional; if it's not present or is blank, CHRONOS assumes the default time type for the output time system (SCET for UTC and ET, SCLK for SCLK and LST for LST);

-FORMAT
  this is used to specify a custom format for the output time; specifying a format on the command line is optional; if a format specification is not present or is blank, CHRONOS looks for a specification in the setup file and, if such is also not available, it uses the default format; note that only times in UTC and ET systems can be formatted as a time time strings on output; refer to Appendix 3 and Appendix 4 for more information on syntax of the output format specifications for time strings and DP numbers;

-TIME
  this is used to specify the input time on the command line; most time types of UTC and ET systems require input time to be in a form of a time string recognized by TIME subsystem of SPICE; refer to Appendix 2 for information on acceptable input time specifications;

-BATCH
  this is used to tell the program to take input time(s) from standard input instead of the command line; if it's present, the program ignores any input time provided after using the ``-TIME'' command line option;

-SC
  this is the NAIF ID for the spacecraft; specifying it on the command line is optional; if the s/c ID is not present on the command line, CHRONOS looks for it in the setup file;

-CENTER
  this is the NAIF ID for the center body; specifying it on the command line is optional; if the center body ID is not present on the command line, CHRONOS looks for it in the setup file;

-LANDINGTIME
  this is the UTC time of the landing; specifying it on the command line is optional; if this time is not present on the command line, CHRONOS looks for it in the setup file;

-SOL1INDEX
  this is the SOL index for the first day on surface; specifying it on the command line is optional; if this index is not present on the command line, CHRONOS looks for it in the setup file;

-NOLABEL
  this is used to tell the program to not display [SYSTEM]/[TYPE] following the output time string;

-TRACE
  this is used to tell the program to display trace information including, complete the command line, names of the loaded SPICE kernel files, all relevant setup information, etc.; this option overrules the ``-NOLABEL'' option;

CHRONOS displays help information if the ``-HELP'' or ``-H'' key is specified on the command line:

          % CHRONOS -HELP|-H

If ``-USAGE'', ``-U'' or nothing is provided on the command line, CHRONOS displays usage information:

          % CHRONOS [-USAGE|-U]

If ``-TEMPLATE'' command line option is specified, CHRONOS displays setup file template:

          % CHRONOS  -TEMPLATE

Command line parameters specified in [] are optional. Command line keys '-XXXXXXX' are case insensitive. Any of the command line options can be present in the command line multiple times (in such cases the last appearance of a key takes precedence.) The order in which options are specified is insignificant.

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### Usage Examples -- Mars Pathfinder

In these examples the command extends over two or three lines with the backslash character indicating continuation. The output appears on the very next line.

The examples below assume that a setup file ``setup.mpf'' exists and contains correct pointers to the needed MPF SPICE kernel files.

To compute SCET UTC for a given HEX SCLK CHRONOS must be run with the following command line options:

       > chronos -setup setup.mpf -from sclk -fromtype hex \
                -to utc -totype scet -time 4A8ADDCA:48
       1997-08-18 16:57:36.110                          (UTC/SCET)
       >

To compute LST for a given UTC/ERT CHRONOS must be run as follows:

       > chronos -setup setup.mpf -from lst -to utc -totype ert \
                -time SOL 12 13:00
       1997-07-16 10:39:34.287                          (UTC/ERT)
       >

In the example above the "-FROMTYPE" option was not needed since the time type used was the default.

The same example using the ``-NOLABEL'' option and formatting the output time ``a-la'' UNIX date command output will look like:

       > chronos -setup setup.mpf -from lst -to utc -totype ert \
                -time SOL 12 13:00 -nolabel \
                -format 'Wkd Month DD HR:MN:SC PDT YYYY ::UTC-7'
       Wed July 16 03:39:34 PDT 1997
       >

Note that in the previous example the ``::UTC-7'' format modifier caused time on the output to be Pacific Day Time (PDT) instead of Greenwich Meridian Time (GMT) which is default time zone for UTC.

The opposite conversion with trace ON (``-TRACE'') will produce the following output (note that in this example CHRONOS recognized PDT token in the input string and processed input time as Pacific Day Time):

       > chronos -setup setup.mpf -from utc -fromtype ert -to lst \
                -time July 16, 1997 3:39:34 PDT -trace

       CHRONOS -- Universal Time Conversion Tool
       Version 1.0.0, May 14, 1998

        Actual command line: -setup setup.mpf -from utc -fromtype ert
                             -to lst -time July 16, 1997 3:39:34 -trace

                 Setup file: setup.mpf

       Loaded SPICE kernels:
                        LSK: using LSK parameters from the setup file.
                       SCLK: /mpf/pds/data/sclk/mpf_final.tsc
                        SPK: /mpf/pds/data/spk/de405.bsp
                        SPK: /mpf/pds/data/spk/mpf_ls.bsp
                        SPK: /mpf/pds/data/spk/mpf_surf.bsp
                         CK: /mpf/pds/data/ck/mpf_ll.bc
                         CK: /mpf/pds/data/ck/mpf_sf.bc
                     FRAMES: /mpf/pds/data/frames/mpf.tfd
                        PCK: using PCK parameters from the setup file.

       Converting time from: UTC/ERT
                         to: LST/LST
         Output time format: NOT APPLICABLE
         Spacecraft NAIF ID: -53
        Center body NAIF ID: 499
          Landing date/time: 1997 JUL 5 09:00
         SOL 1 midnight UTC: 1997 JUL 04 13:53:14.703
       Average local second: 1.0277116753731E+00 ET seconds

       July 16, 1997 3:39:34                                (UTC/ERT)
       SOL 12 13:00:00                                      (LST/LST)

       >

In the next example CHRONOS is used to convert a few UTC/SCET times provided in an external file ``input.times'' (each input time on a line by itself with no blank line between them) to the corresponding SCLK times written to an output file ``output.times'':

       > chronos -setup setup.mpf -from utc -to sclk \
                -batch -nolabel < input.times > output.times
       >

If input file ``input.times'' contained the following lines:

       1997-07-06 12:00:00.000
       1997-07-06 13:00:00.000
       1997-07-06 14:00:00.000
       1997-07-06 15:00:00.000

then output file ``output.times'' will contain:

       3/1246881607.104
       3/1246885207.101
       3/1246888807.099
       3/1246892407.096

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### Using CHRONOS with Calling Scripts or Aliases

Specifying all command line options every time you run the program can be quite tiring, especially taking into account that most command lines require several character strings and selected combinations of input/output time systems/types are probably used many times. Therefore, it could be very convenient to define a set of aliases or create a number of wrapper scripts which will contain preset combinations of command line parameters for a given input/output time system/type pair. For example, conversion from UTC/SCET to UTC/ERT can be implemented by the following alias:

       alias utc2ert 'chronos -from utc  -fromtype scet -to utc  \
                     -totype ert  -format -time'

or c-shell script ``utc2ert'':

       #!/bin/csh -f
       chronos -from utc  -fromtype scet -to utc \
                     -totype ert  -format -time $argv[*]

Then to perform the conversion you need to type only

       > utc2ert 1998 jan 12 13:00
       1998-01-12 13:18:04.672                                 (UTC/ERT)
       >

Note that since for both the alias and the script a setup file name wasn't specified on the command line, CHRONOS used the name provided in the environment variable CHRONOS_SETUP_FILE.

A set of aliases mimicking time tools that were used by the Mars Pathfinder project is provided in Appendix 1 at the end of the document. It doesn't cover all possible combinations of the input/output time system/type pairs but it could be easily extended to do so.

Using aliases makes using CHRONOS easy, but it seems that by setting command line options in these aliases we are taking away some of the program's flexibility. This is not true. That CHRONOS allows any command line option to be specified as many times as desired (then the last appearance/value of it is used) and that blank values are permitted, allows one to use any pre-specified alias in the same way as the program itself.

For example, if you want to specify a custom output format while using the ``utc2ert'' alias, it can be done with the ``-FORMAT'' command line option as it would be while using CHRONOS without any wrappers:

       > utc2ert 1998 JAN 12 11:24 -format YYYY-DOY//HR:MN:SC

or

       > utc2ert -format YYYY-DOY//HR:MN:SC -time 1998 JAN 12 11:24

or

       > utc2ert -time 1998 JAN 12 11:24 -format YYYY-DOY//HR:MN:SC

Note that in the first case the ``-TIME'' command line option wasn't needed because it's already present in the ``utc2ert'' alias, while in the second example it was required to tell the program that ``1998 JAN 12 11:24'' is an input time but not a part of the format string specified after ``-FORMAT''. In the third case, it seems that we have the ``-TIME'' key repeated two times because it's present in the alias and on the command line. This is not a problem for CHRONOS, it just ignores the first ``-TIME'' and the blank value which appears after it.

This example can be easily extended to demonstrate other possibilities:

`--` using a different setup file:

                > utc2ert -setup setup.m98lnd -time 1998 JAN 12 11:24

`--` turning tracing ON:

                > utc2ert 1998 JAN 12 11:24 -trace

`--` running in the batch mode:

                > utc2ert -batch < input.times > output.times

`--` using a different output time type:

                > utc2ert -totype ett -time 1998 JAN 12 11:24

`--` or a combination of all of the above:

                > utc2ert -setup setup.m98lnd \
                          -totype ett \
                          -trace \
                          -batch < input.times > output.times

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## Setup File

CHRONOS requires a few parameters to be provided in a setup file. The name of a setup file is usually provided on the command line. If it's not present there, the program looks for the name associated with the environment variable CHRONOS_SETUP_FILE.

The setup file format must follow the SPICE Kernel Text file format rules, i.e. it must contain data formatted as a set of KEYWORD=VALUE assignments enclosed between

       \begindata
       \begintext

markers. Each assignment and marker must be on a line by itself.

The following parameters may be provided in a setup file:

       \begindata
          LEAPSECONDS_FILE  = 'name of a LSK file'
          SCLK_FILE         = 'name of a SCLK file for the mission'
          PCK_FILE          = 'name of a PCK file'
          SPK_FILES         = ( 'name of an SPK file', '...' )
          CK_FILES          = ( 'name of a CK file', '...' )
          FRAMES_FILE       = 'name of a frame definitions file'
          SPACECRAFT_ID     = NAIF ID for the spacecraft
          CENTER_ID         = NAIF ID for the center body
          LANDING_TIME      = 'UTC time of the landing'
          LANDING_SOL_INDEX = SOL index of the landing
       \begintext

Note that either or all of the SPACECRAFT_ID, CENTER_ID, LANDING_TIME, and LANDING_SOL_INDEX parameters can also be provided using the command line switches. If done so, the setup file value corresponding to a command line value is not needed, and, if present, is ignored by the program.

Similarly, the kernels files to be loaded can be provided using the standard SPICE interface -- with the KERNELS_TO_LOAD parameter:

       \begindata
          KERNELS_TO_LOAD = (
                             'name of a LSK file',
                             'name of a SCLK file ',
                             'name of a PCK file',
                             'name of an SPK file',
                             '...',
                             'name of a CK file',
                             '...',
                             'name of an FK file'
                            )
       \begintext

or using KERNELS_TO_LOAD with additional path specification keywords -- PATH_VALUES/PATH_SYMBOLS:

       \begindata
          PATH_VALUES      = (
                              '/directory/where/kernels/are'
                             )
          PATH_SYMBOLS     = (
                              'KERNELS'
                             )
          KERNELS_TO_LOAD  = (
                              '$KERNELS/name of a LSK file',
                              '$KERNELS/name of a SCLK file ',
                              '$KERNELS/name of a PCK file',
                              '$KERNELS/name of an SPK file',
                              '$KERNELS/...',
                              '$KERNELS/name of a CK file',
                              '$KERNELS/...',
                              '$KERNELS/name of an FK file'
                             )
       \begintext

or even by simply listing them after the -SETUP command line switch. If KERNELS_TO_LOAD, or KERNELS_TO_LOAD + PATH_VALUES/PATH_SYMBOLS, or listing kernel names directly on the command line is used, specifying the LEAPSECONDS_FILE, SCLK_FILE, PCK_FILE, SPK_FILES, CK_FILES, and FRAMES_FILE setup file parameters is not necessary.

Note that if some data from the LSK or PCK kernels is included directly into the setup file, they get loaded into the program automatically. In such cases program checks whether required LSK values are already loaded and if so it's doesn't load external LSK file(s).

Custom format for a particular time system/type pair can be specified in a setup file using keywords [SYSTEM]_{TYPE}_FORMAT, where [SYSTEM] and {TYPE} are corresponding character designations (for example: UTC_SCET_FORMAT = 'YYYY-DOY//HR:MN')

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### Setup File Examples

Below are three setup file examples. The first one is for MER-2, the second one is the M98 Lander, and the third one is for Mars Pathfinder.

MER-2 CHRONOS setup file, using FURNSH-style kernel file name specification:

       \begindata
          PATH_VALUES       = (
                              '/ftp/pub/naif/MER/kernels'
                              )
          PATH_SYMBOLS      = (
                              'KERNELS'
                              )
          KERNELS_TO_LOAD   = (
                              '$KERNELS/lsk/naif0007.tls'
                              '$KERNELS/sclk/MER_254_SCLKSCET.00003.tsc'
                              '$KERNELS/pck/mars_iau2000_v0.tpc'
                              '$KERNELS/spk/de410.bsp'
                              '$KERNELS/spk/mer2_ls_ep55a2_iau2000_v1.bsp'
                              '$KERNELS/spk/mer2_still_at_ls_v1.bsp'
                              )
          SPACECRAFT_ID     = -254
          CENTER_ID         = 499
          LANDING_TIME      = '2004-01-04 04:20'
          LANDING_SOL_INDEX = 1
       \begintext

       Sun GM from pck00006.tpc.

       \begindata
          BODY10_GM  =   132712440041.939
       \begintext

M98 Lander CHRONOS setup file:

       \begindata
          LEAPSECONDS_FILE = '/kernels/gen/lsk/naif0006.tls'
          SCLK_FILE = '/kernels/m98lnd/sclk/m98lnd.test.tsc'
          PCK_FILE = '/kernels/gen/pck/pck00006.tpc'
          SPK_FILES = (
                      '/kernels/gen/spk/de405s.bsp',
                      '/kernels/m98lnd/spk/landsite/m98lndst.bsp'
                       )
          SPACECRAFT_ID = -116
          CENTER_ID = 499
          LANDING_TIME = '1999 DEC 1 12:00'
          LANDING_SOL_INDEX = 0
       \begintext

MPF CHRONOS setup file:

       =====================================================
       CHRONOS Setup Keywords.
       =====================================================
       \begindata
          LEAPSECONDS_FILE = '/mpf/pds/data/lsk/mpf.tls'
          SCLK_FILE = '/mpf/pds/data/sclk/mpf_final.tsc'
          PCK_FILE = '/mpf/pds/data/pck/mpf.tpc'
          SPK_FILES = (
                       '/mpf/pds/data/spk/de405.bsp',
                       '/mpf/pds/data/spk/mpf_ls.bsp',
                       '/mpf/pds/data/spk/mpf_surf.bsp'
                       )
          CK_FILES = (
                       '/mpf/pds/data/ck/mpf_ll.bc',
                       '/mpf/pds/data/ck/mpf_sf.bc'
                       )
          FRAMES_FILE = '/mpf/pds/data/frames/mpf.tfd'
          SPACECRAFT_ID = -53
          CENTER_ID = 499
          LANDING_TIME = '1997 JUL 5 09:00'
          UTC_ERT_FORMAT = 'YYYY-DOY//HR:MN:SC.### ERT'
          UTC_SCET_FORMAT = 'YYYY-DOY//HR:MN:SC.###'
          ET_SCET_FORMAT = 'YYYY-DOY//HR:MN:SC.### ET-ERT'
          ET_ERT_FORMAT = 'YYYY-DOY//HR:MN:SC.### ET'
       \begintext
       =====================================================
       Required LSK parameters. Extracted from naif0006.tls.
       =====================================================
       \begindata
          DELTET/DELTA_T_A       =   32.184
          DELTET/K               =    1.657D-3
          DELTET/EB              =    1.671D-2
          DELTET/M               = (  6.239996D0   1.99096871D-7 )
          DELTET/DELTA_AT        = ( 10,   @1972-JAN-1
                                     11,   @1972-JUL-1
                                     12,   @1973-JAN-1
                                     13,   @1974-JAN-1
                                     14,   @1975-JAN-1
                                     15,   @1976-JAN-1
                                     16,   @1977-JAN-1
                                     17,   @1978-JAN-1
                                     18,   @1979-JAN-1
                                     19,   @1980-JAN-1
                                     20,   @1981-JUL-1
                                     21,   @1982-JUL-1
                                     22,   @1983-JUL-1
                                     23,   @1985-JUL-1
                                     24,   @1988-JAN-1
                                     25,   @1990-JAN-1
                                     26,   @1991-JAN-1
                                     27,   @1992-JUL-1
                                     28,   @1993-JUL-1
                                     29,   @1994-JUL-1
                                     30,   @1996-JAN-1
                                     31,   @1997-JUL-1 )
       \begintext
       =====================================================
       Required PCK constants. Extracted from pck00006.tpc.
       =====================================================
       \begindata
          BODY499_POLE_RA          = (  317.68143     -0.1061       0.  )
          BODY499_POLE_DEC         = (  +52.88650     -0.0609       0.  )
          BODY499_PM               = (  176.901   +350.89198226     0.  )
          BODY10_GM  =   132712440041.939
       \begintext

Note that in MPF case more SPICE data is needed to support time conversions. It even needs some CK files. The reason is that MPF Lander location in the corresponding SPK file is given relative to the surface fixed frame rather than relative to the center on Mars in the Mars fixed frame as is done for the M98 Lander. Therefore, to compute the location of the MPF Lander relative to the Sun or Earth, which is needed for converting from/to local time or for computing ERT or ETT, CHRONOS needs to load all SPICE kernels containing positions and frame transformation information needed to perform such computations.

The setup file for MPF also contains DOY-style output format pictures for UTC/ERT, UTC/SCET, ERT/ERT and ER/SCET system/types.

As already mentioned CHRONOS automatically loads any KEYWORD=VALUE definitions present in the setup file. This can be used to speed program execution by placing required LSK and PCK parameters in the setup file instead of making the program read them from standard LSK and PCK files which will take more time. (Loading data only from one file is is much quicker than loading data from two or three text kernels.)

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## Appendix 1: Aliases Mimicing MPF Time Tools

The following command line time conversion utilities were created by the MPF NAV team (Robin Vaughan) and widely used by MPF during mission operations:

       ert2hex   hex2ert   lst2ert   sclk2ert   sol2ert   utc2ert
       ert2lst   hex2lst   lst2hex   sclk2hex   sol2hex   utc2ett
       ert2ltmst hex2ltmst lst2ltmst sclk2lst   sol2sclk  utc2hex
       ert2sclk  hex2sclk  lst2sclk  sclk2ltmst sol2utc   utc2lst
       ert2utc   hex2utc   lst2utc   sclk2utc             utc2lsun
                                                          utc2ltmst
                                                          utc2sclk

In the above tool names:

``utc''
  represented the system/type UTC/SCET;

``ert''
  UTC/ERT;

``ett''
  UTC/ETT;

``hex''
  SCLK/HEX;

``sclk''
  SCLK/SCLK;

``sol''
  approximation of the LST/LST computed using interpolation over precalculated local midnight UTC times; this time contained SOL day number;

``lsun''
  LST/LSUN;

``ltmst''
  local true solar time (equivalent of CHRONOS's LST/LST) and local mean solar time computed using mean Sun position;

``lst''
  approximation of the LST/LST computed using interpolation over precalculated local midnight UTC times; this time contained year and day;

Most of these utilities (except those dealing with approximated local times):

       ert2hex   hex2ert   sclk2ert   sol2ert   utc2ert
       ert2sol   hex2sol   sclk2hex   sol2hex   utc2hex
       ert2sclk  hex2sclk  sclk2sol   sol2sclk  utc2sol
       ert2utc   hex2utc   sclk2utc   sol2utc   utc2sclk
                                                utc2lsun
                                                utc2ett

can be implemented by using aliases to CHRONOS with the right combination of command line options. Note that in aliases ``sol'' designates LST/LST rather than approximated local solar time as it was on MPF.

The c-shell script ``mpf.chronos.aliases'' shown below sets these aliases. The aliases in the script must be made available to the UNIX c-shell by loading the script with the ``source'' command:

       > source mpf.chronos.aliases

``mpf.chronos.aliases'' script:

       alias ert2hex  'chronos -from utc  -fromtype ert       \'\
                             '-to   sclk -totype   hex  -time'
       alias ert2sol  'chronos -from utc  -fromtype ert       \'\
                             '-to   lst  -totype   lst  -time'
       alias ert2sclk 'chronos -from utc  -fromtype ert       \'\
                             '-to   sclk -totype   sclk -time'
       alias ert2utc  'chronos -from utc  -fromtype ert       \'\
                             '-to   utc  -totype   scet -time'
       alias hex2ert  'chronos -from sclk -fromtype hex       \'\
                             '-to   utc  -totype   ert  -time'
       alias hex2sol  'chronos -from sclk -fromtype hex       \'\
                             '-to   lst  -totype   lst  -time'
       alias hex2sclk 'chronos -from sclk -fromtype hex       \'\
                             '-to   sclk -totype   sclk -time'
       alias hex2utc  'chronos -from sclk -fromtype hex       \'\
                             '-to   utc  -totype   scet -time'
       alias sol2ert  'chronos -from lst  -fromtype lst       \'\
                             '-to   utc  -totype   ert  -time'
       alias sol2hex  'chronos -from lst  -fromtype lst       \'\
                             '-to   sclk -totype   hex  -time'
       alias sol2sclk 'chronos -from lst  -fromtype lst       \'\
                             '-to   sclk -totype   sclk -time'
       alias sol2utc  'chronos -from lst  -fromtype lst       \'\
                             '-to   utc  -totype   scet -time'
       alias sclk2ert 'chronos -from sclk -fromtype sclk      \'\
                             '-to   utc  -totype   ert  -time'
       alias sclk2hex 'chronos -from sclk -fromtype sclk      \'\
                             '-to   sclk -totype   hex  -time'
       alias sclk2sol 'chronos -from sclk -fromtype sclk      \'\
                             '-to   lst  -totype   lst  -time'
       alias sclk2utc 'chronos -from sclk -fromtype sclk      \'\
                             '-to   utc  -totype   scet -time'
       alias utc2ert  'chronos -from utc  -fromtype scet      \'\
                             '-to   utc  -totype   ert  -time'
       alias utc2et   'chronos -from utc  -fromtype scet      \'\
                             '-to   et   -totype   scet -time'
       alias utc2hex  'chronos -from utc  -fromtype scet      \'\
                             '-to   sclk -totype   hex  -time'
       alias utc2sol  'chronos -from utc  -fromtype scet      \'\
                             '-to   lst  -totype   lst  -time'
       alias utc2sclk 'chronos -from utc  -fromtype scet      \'\
                             '-to   sclk -totype   sclk -time'
       alias utc2lsun 'chronos -from utc  -fromtype scet      \'\
                             '-to   lst  -totype   lsun -time'
       alias utc2ett  'chronos -from utc  -fromtype scet      \'\
                             '-to   utc  -totype   ett  -time'

Note that each of the command defined by these aliases will expect a setup file name to be provided using the CHRONOS_SETUP_FILE environment variable unless aliases are modified to include it on the command line using the ``-SETUP'' option.

Top

## Appendix 2: Input UTC and ET Time string formats

UTC/(SCET,ERT,ETT) and ET/(SCET,ERT,ETT) times used as input must be provided as time strings that can be parsed by the SPICE STR2ET routine. Below is an extract from the STR2ET subroutine header, explaining acceptable formats and providing some examples.

       The variety of ways people have developed for representing
       times is enormous. It is unlikely that any single subroutine
       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, UNIX
       `date` output formats, VMS time formats, MS-DOS formats,
       etc.  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,
       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 routine TPARTV.

       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 can then
       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 UT

       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 )

       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 UT

         1988 June 13, 12:29:48 UTC.

       Note that you may not specify two different time systems
       simultaneously.  For example

         1988 June 13, 12:29:48 PDT TDT

       You might be able to make some kind of reasonable guess as
       to the meaning of this string, but we've decided to regard
       such strings as errors.

       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 unlabelled, it is regarded
       as representing a string in the UTC time system on the
       Gregorian calendar.  Abbreviated years are
       regarded as abbreviations of the years from 1969 to 2068.

       You may modify these defaults through the routines TIMDEF
       and TSETYR (an entry point of TEXPYR).

       You may:

         Set the calendar to be Gregorian, Julian or a mixture of
         the two using TIMDEF;

         Set the time system to be UTC, TDB, TDT or any time zone
         using TIMDEF;

         Set the range of year abbreviations to be any 100 year
         interval using TSETYR.

       See the routines TEXPYR and TIMDEF for details on changing
       defaults.

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

       If some component of a date or time is "out-of-range" STR2ET
       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 28 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 and
       time systems have clear meanings.  However, the meaning of
       a numeric component must be deciphered from its magnitude
       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 does not
           support such strings.

           No exponential components are allowed.  For example you
           can't input 1993 Jun 23 23:00:01.202E-4 you have
           to explicitly list all zeros that follow the decimal
           point: i.e.  1993 Jun 23 23:00:00.0001202

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

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

       7)  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 TEXPYR
           for further discussion of abbreviated years.

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

        9) 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
           to modify this behavior.

       10) If the International Standard Organization (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.

       11) 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, forward
           slash, period, day of year mark "//" or "::" )

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

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

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

       14) 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
       --------

       Below is a sampling of some of the time formats that
       are acceptable as inputs to STR2ET and the way they
       are interpreted. A complete discussion
       of permissible formats is given in the SPICE routine
       TPARTV as well as in this document reference file time.req
       located in the /doc directory of the toolkit. "na"
       means Not Applicable.

       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 SPICE routine TSETYR. 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 and STR2ET, 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.
       ...

Top

## Appendix 3: Output Time String Formatting Rules

UTC/(SCET,ERT,ETT) and ET/(SCET,ERT,ETT) times output from CHRONOS are formatted as time string in accordance with the format picture specification recognized by SPICE's TIMOUT routine. Below is an extract from the TIMOUT subroutine header, explaining acceptable specifications of output format pictures and providing some examples.

       A format picture is simply a string of letters that lets
       TIMOUT know where various components of a time representation
       should be placed during creation of the time string.
       Here's an example of such a picture:

          MON DD,YYYY  HR:MN:SC.#### (TDB) ::TDB

       Here is a sample of times that would be created by
       using this format.

          JAN 12,1992  12:28:18.2772 (TDB)
          FEB 13,1994  23:18:25.2882 (TDB)
          AUG 21,1995  00:02:00.1881 (TDB)

       As you can see from the samples above, the format picture
       specifies that every time string created should begin
       with a three-letter abbreviation for the month, followed
       by a space and the day of the month. The day of month is
       followed immediately by a comma and the year. The year
       component is followed by two spaces. The next outputs are
       hours represented as a two digit integer, a colon, minutes as
       represented a two digit integer, another colon, and seconds
       rounded to 4 decimal places and having a two digit integer
       part. This is followed by a space and the string (TDB). The
       special marker `::TDB' in the time picture is an
       ``invisible'' marker. It is used to specify the time
       system that should be used in creating the time string
       (in this case Barycentric Dynamical Time).

       TIMOUT does not recognize all of the parts of the time
       format picture in the example above. The list of recognized
       parts and unrecognized parts is shown in the table below.

         Recognized       Unrecognized
         ----------       ------------
         'MON'            ' '
         'DD'             ','
         'YYYY'           '  '
         'HR'             ':'
         'MN'             '(TDB)'
         'SC'
         '.####'
         '::TDB'

       The unrecognized parts are called literal markers.  They are
       copied exactly as they appear in PICTUR into the output string.
       The recognized parts of the picture are replaced by a
       component of time or, as in the case of `::TDB', are used
       as instructions about the overall properties of the time
       string.

       The full list of recognized markers, their classification
       and meaning are given below.

       MARKER       CLASS     MEANING
       -----------  --------  -----------------------------------------
       '.##...'     modifier  represent a numeric   component that
                              immediately precedes this in a decimal
                              format.  Number of decimal places
                              equals the number of '#'  characters
       '::GCAL'     meta      dates are reported in Gregorian Calendar
       '::JCAL'     meta      dates are reported in Julian Calendar
       '::MCAL'     meta      dates after 15 October, 1582 are reported
                              in Gregorian Calendar, before that
                              dates are reported in Julian Calendar

       '::RND'      meta      round output to places specified by
                              least significant component

       '::TDB'      meta      all components should be TDB

       '::TDT'      meta      all components should be TDT

       '::TRNC'     meta      truncate all output components (default)
       '::UTC'      meta      all components should be UTC (default)
       '::UTC+h:m'  meta      all components in UTC offset by +h (hours)
                              and +m (minutes) so as to allow time zones.
       '::UTC-h:m'  meta      all components in UTC offset by -h (hours)
                              and -m (minutes) so as to allow time zones.
       'AMPM'       string    String (either 'A.M.'  or 'P.M.')
                              indicating whether hours are before
                              or after noon.
       'ampm'       string    String (either 'a.m.'  or 'p.m.')
                              indicating whether hours are before
                              or after noon.
       'AP'         numeric   AM/PM equivalents of the hour component
                              of a time.
       'DD'         numeric   Day of month
       'DOY'        numeric   Day of year
       'ERA'        string    String (either 'B.C.'  or 'A.D.') giving
                              era associated with an epoch.
       'era'        string    String (either 'b.c.'  or 'a.d.') giving
                              era associated with an epoch.
       'HR'         numeric   hour component of time
       'JULIAND'    numeric   Julian date component of time
       'MM'         numeric   numeric representation of month component
       'MN'         numeric   minute component of time
       'MON'        string    upper case three letter abbreviation for
                              month
       'Mon'        string    capitalized three letter abbreviation for
                              month
       'mon'        string    lower case three letter abbreviation for
                              month
       'MONTH'      string    upper case full name of month
       'Month'      string    capitalized full name of month
       'month'      string    lower case full name of month
       'SC'         numeric   seconds component of time
       'SP1950'     numeric   seconds past 1950 component of time
       'SP2000'     numeric   seconds past 2000 component of time
       'YR'         numeric   last two digits of year component of time
       'YYYY'       numeric   year component of time
       'WEEKDAY'    string    upper case day of week
       'Weekday'    string    capitalized day of week
       'weekday'    string    lower case day of week
       'WKD'        string    upper case three letter abbreviation for
                              day of week.
       'Wkd'        string    capitalized three letter abbreviation for
                              day of week.
       'wkd'        string    lower case three letter abbreviation for
                              day of week.

       String Markers

          String markers are portions of the format picture that
          will be replaced with a character string that represents
          the corresponding component of a time.

       Numeric Markers

          Numeric markers are portions of the format picture that
          will be replaced with a decimal string that represents
          the corresponding component of a time.

       Meta Markers

          Meta markers (listed under the class ``meta'' in the
          table above) are used to indicate `global' properties of
          your time string. You may specify time scale and how
          rounding should be performed on the components of time
          in your output string. Meta markers may be placed anywhere
          in your format picture. They do not contribute to placement
          of characters in output time strings. Also there are no
          restrictions on how many meta markers you may place in
          the format picture. However, if you supply conflicting
          `meta' markers (for example ::TDT and ::TDB) in your
          picture the first marker listed (in left to right order)
          overrules the conflicting marker that appears later in
          the picture.

       Default Meta Markers

          If you do not specify a time system, calendar, or time
          zone through the use of a Meta Marker, TIMOUT uses the
          values returned by the SPICE routine TIMDEF. The default
          time system, calendar returned by TIMDEF are UTC and
          the Gregorian calendar.  The default time zone returned
          by TIMDEF is a blank indicating that no time zone offset
          should be used.

          See the header for the routine TIMDEF for a more complete
          discussion of setting and retrieving default values.

       Modifier Markers

          The numeric markers listed in the table above stand
          for integers unless they are modified through use of a
          modifier marker. The strings

             .#
             .##
             .###
             .####

          are used to this end. When a numeric marker is followed
          immediately by one of these modifiers, the corresponding
          time component will be written with the number of decimal
          places indicated by the number of successive occurrences of
          the character '#'. Any numeric token may be modified.

       Rounding vs. Truncation

          The meta markers ::TRNC and ::RND allow you to control
          how the output time picture is rounded. If you specify
          ::TRNC all components of time are simply truncated to
          the precision specified by the marker and any modifier.
          If you specify ::RND the output time is rounded to the
          least significant component of the format picture. The
          default action is truncation.

          Whether an output time string should be rounded or
          truncated depends upon what you plan to do with the
          string. For example suppose you simply want to get the
          calendar date associated with a time and not the time of
          day. Then you probably do not want to round your output.
          Rounding 1992 Dec 31, 13:12:00 to the nearest day
          produces 1993 Jan 1. Thus in this case rounding is probably
          not appropriate.

          However, if you are producing output for plotting using
          Julian Date, seconds past 1950 or seconds past
          2000, you will probably want your output rounded so as
          to produce a smoother plot.

       Time Systems

          TIMOUT can produce output strings for epochs relative to
          any of the three systems UTC, TDT, or TDB.  If you do not
          explicitly specify a time system, TIMOUT will produce strings
          relative to the time system returned by the SPICE routine
          TIMDEF.  Unless you call TIMDEF and change it, the default time
          system is UTC.  However, by using one of the Meta Markers
          ::UTC, ::TDT, or ::TDB you may specify that TIMOUT produce
          time strings relative to the UTC, TDT, or TDB system
          respectively.

       Time Zones

          The meta markers ::UTC+h:m  and ::UTC-h:m  allow you
          offset UTC times so that you may represent times in
          a time zone other than GMT.  For example you can
          output times in Pacific Standard time by placing the
          meta-marker ::UTC-8 in your format picture.

          For instance, if you use the picture

             YYYY Mon DD, HR:MN:SC ::UT

          you will get output strings such as:

             1995 Jan 03, 12:00:00

          If you use the picture

             YYYY Mon DD, HR:MN:SC ::UTC-8

          you will get output strings such as:

             1995 Jan 03, 04:00:00

          Finally, if you use the picture

             YYYY Mon DD, HR:MN:SC ::UTC-8:15

          you will get output strings such as

             1995 Jan 03, 03:45:00

          Note that the minutes are always added or subtracted
          based on the sign present in the time zone specifier.
          In the case of ::UTC+h:m, minutes are added. In the
          case ::UTC-h:m, minutes are subtracted.

          The unsigned part of the hours component can be no more
          than 12.  The unsigned part of the minutes component can
          be no more than 59.

       Calendars

          The calendar currently used by western countries is the
          Gregorian calendar.  This calendar begins on Oct 15, 1582.
          Prior to Gregorian calendar the Julian calendar was used.
          The last Julian calendar date prior to the beginning
          of the Gregorian calendar is Oct 5, 1582.

          The primary difference between the Julian and Gregorian
          calendars is in the determination of leap years.
          Nevertheless both can be formally extended backward and
          forward in time indefinitely.

          By default TIMOUT uses the default calendar returned by TIMDEF.
          Under most circumstances this will be the Gregorian calendar
          (::GCAL).  However you may specify that TIMOUT use a specific
          calendar through use of one of the calendar Meta Markers. You
          may specify that TIMOUT use the Julian calendar (::JCAL), the
          Gregorian calendar (::GCAL)  or a mixture of both (::MCAL).

          If you specify ::MCAL, epochs that occur after the
          beginning of the Gregorian calendar will be represented
          using the Gregorian calendar and epochs prior to the
          beginning of the Gregorian calendar will be represented
          using the Julian calendar.

       Getting Software to Construct Pictures for You.

          Although it is not difficult to construct time format
          pictures, you do need to be aware of the various markers
          that may appear in a format picture.

          There is an alternative means for getting a format picture.
          The routine TPICTR constructs format pictures from a sample
          time string. For example, suppose you would like your
          time strings to look like the basic pattern of the string
          below.

             'Fri Jul 26 12:22:09 PDT 1996'

          You can call TPICTR with this string, and it will create
          the appropriate PICTUR for use with TIMOUT.

             CALL TPICTR ( 'Fri Jul 26 12:22:09 PDT 1996', PICTUR, OK )

          The result will be:

             'Wkd Mon DD HR:MN:SC (PDT) ::UTC-7'

          Note: not every date that you can read is interpretable
          by TPICTR.  For example, you might be able to understand
          that 19960212121116 is Feb 2 1996, 12:11:16.  However,
          TPICTR cannot recognize this string.  Thus it is important
          to check the logical output OK to make sure that TPICTR was
          able to understand the time picture you provided.

          Even thought TPICTR can not recognize every time pattern
          that has been used by various people, it does recognize
          nearly all patterns that you use when you want to communicate
          outside your particular circle of colleagues.
       ...

Top

## Appendix 4: Output DP Number Formatting Rules

On output UTC/LT, ET/(LT,SECONDS) and LST/LSUN are formatted as DP numbers in accordance with a format picture specification recognized by SPICE's DPFMT routine. Below is an extract from the DPFMT subroutine header explaining acceptable specifications of an output DP format picture and providing some examples.

       Format Picture Construction Rules
       ---------------------------------

       A format picture is a string used to describe the format of
       the output string.  There are four special characters
       recognized by DPFMT --- a leading + or -, a leading
       zero ( '0' ) or a zero that follows a leading + or -,
       and the first decimal point of the string.

       All other non-blank characters are regarded as
       equivalent.  The picture ends at the first blank
       character.  The effects associated with the various
       characters in a picture are spelled out in the
       description of the output STRING.

       The following pictures are treated as errors.

       ' ', '+', '-', '.', '+.', '-.'

       If the first character of the picture is a minus sign,
       the first character in the output string will be
       a blank if the number is non-negative, a minus sign
       if the number is negative.

       If the first character of the picture is a plus sign,
       the first character of the output string will be a
       plus if the number is positive, a blank if the number
       is zero, and a minus sign if the number is negative.

       If the first character of the string is NOT a sign
       (plus or minus) the first character of the output
       string will be a minus sign if the number is negative
       and will be the first character of the integer part
       of the number otherwise.

       The integer portion of STRING will contain the same
       number of characters as appear before the decimal point
       (or last character if there is no decimal point) but
       after a leading + or -.

       If the picture begins with any of the following

          '+0', '-0', or '0'

       it is said to have a leading zero.  If a picture has
       a leading zero and the integer portion is not large
       enough to fill up the integer space specified by
       PICTUR, STRING will be zero padded from the sign (if
       one is required) up to the first character of the
       integer part of the number.

       If picture does NOT have a leading zero and
       the integer portion is not large enough to fill up
       the space specified by PICTUR, STRING will be blank
       padded on the left between the sign (if one is required)
       and the first character of the integer part of the
       number.

       If a decimal point ( '.' ) is present in PICTUR it
       will be present following the integer portion of
       STRING. Moreover, the decimal portion of STRING will
       contain the same number of digits as there are
       non-blank characters following the decimal point in
       PICTUR.  However, only the first 14 digits starting
       with the first non-zero digit are meaningful.

       If the format specified by PICTUR does not provide
       enough room for the integer portion of X, the routine
       determines whether or not the number of characters
       present in the picture is sufficient to create a
       representation for X using scientific notation.  If
       so, the output is displayed using scientific notation
       (leading signs if they are present in PICTUR, will
       also appear in STRING).   If the format specified
       by PICTUR is too short to accommodate scientific
       notation, the output string is filled with '*' to
       the same length as the length of PICTUR. Leading
       signs are not preserved in this overflow case.

       Examples
       --------

       Suppose that X has the binary representation of PI.
       Then the table below illustrates the strings that
       would be produced by a variety of different pictures.

       PICTUR         |    STRING
       -------------------------------
       '0x.xxx'       |  '03.142'
       'xx.xxx'       |  ' 3.142'
       '+xxx.yyyy'    |  '+  3.1416'
       '-.yyyy'       |  '******'
       'xxxxxxxx'     |  '       3'
       '00xx'         |  '0003'
       '-00.0000000'  |  ' 03.1415927'
       '00'           |  '03'
       'x.'           |  '3.'
       '.mynumber'    |  '3.142E+00'
       'my dog spot'  |  ' 3'
       'my.dog spot'  |  ' 3.142'
       '+my.dog,spot' |  '+ 3.14159265'

       Suppose that X has the binary representation of 2/3.
       Then the table below illustrates the strings that
       would be produced by a variety of different pictures.

       PICTUR         |    STRING
       -------------------------------
       '+x.xxx'       |  '+0.667'
       '+xx.xxx'      |  '+ 0.667'
       'xxx.yyyy'     |  '  0.6667'
       '.yyyy'        |  '.6667'
       'xxxxxxxx'     |  '       1'
       '00xx'         |  '0001'
       '-0.0000000'   |  ' 0.6666667'
       '00'           |  '01'
       'x.'           |  '1.'
       'mynumber'     |  '       1'
       'my dog spot'  |  ' 1'
       'my.dog spot'  |  ' 0.667'
       'my.dog,spot'  |  ' 0.66666667'

       Suppose that X has the binary representation of
       -8/9. Then the table below illustrates the strings
       that would be produced by a variety of different
       pictures.

       PICTUR         |    STRING
       -------------------------------
       '+x.xxx'       |  '-0.889'
       '-00.xxxx'     |  '-00.8889'
       'xxx.xxx'      |  ' -0.889'
       '000.000'      |  '-00.889'