CHRONOS User's Guide =========================================================================== Last revised on 2021 SEP 10 by M. Costa Sitja. Abstract -------------------------------------------------------- CHRONOS is a command-line program that converts between several time systems and time formats. 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. 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. 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. 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; 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. 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 -FROM <"from" time system> [-FROMTYPE <"from" time type>] -TO <"to" time system> [-TOTYPE <"to" time type>] [-FORMAT ] -TIME | -BATCH [-SC ] [-CENTER ] [-LANDINGTIME ] [-SOL1INDEX ] [-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. 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 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 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/...', '$KERNELS/name of an FK file' ) \begintext or even by simply listing them after the -SETUP command line switch. If KERNELS_TO_LOAD, or KERNELS_TO_LOAD + PATH_VALUES/PATH_SYMBOLS, or listing kernel names directly on the command line is used, specifying the LEAPSECONDS_FILE, SCLK_FILE, PCK_FILE, SPK_FILES, CK_FILES, and FRAMES_FILE setup file parameters is not necessary. Note that if some data from the LSK or PCK kernels is included directly into the setup file, they get loaded into the program automatically. In such cases program checks whether required LSK values are already loaded and if so it's doesn't load external LSK file(s). Custom format for a particular time system/type pair can be specified in a setup file using keywords [SYSTEM]_{TYPE}_FORMAT, where [SYSTEM] and {TYPE} are corresponding character designations (for example: UTC_SCET_FORMAT = 'YYYY-DOY//HR:MN') Setup File Examples Below are three setup file examples. The first one is for MER-2, the second one is the M98 Lander, and the third one is for Mars Pathfinder. MER-2 CHRONOS setup file, using FURNSH-style kernel file name specification: \begindata PATH_VALUES = ( '/ftp/pub/naif/MER/kernels' ) PATH_SYMBOLS = ( 'KERNELS' ) KERNELS_TO_LOAD = ( '$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.) 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. 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. ... 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. ... 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'