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SPKMERGE User's Guide

Table of Contents 


   SPKMERGE User's Guide
      Abstract
      Introduction
      Running SPKMERGE
      Command file syntax
      Command file keywords
         LEAPSECONDS_KERNEL
         SPK_KERNEL
         SOURCE_SPK_KERNEL
         BODIES
         BEGIN_TIME, END_TIME
         LOG_FILE
         INCLUDE_COMMENTS


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SPKMERGE User's Guide




Last revised on 2014 JAN 21 by B. V. Semenov.



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Abstract



SPKMERGE is a program that subsets or merges one or more SPK files into a single SPK file.



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Introduction



SPKMERGE builds new SPK files by merging entire or subsets of one or more existing SPK files. SPKMERGE creates SPK kernels that have no overlapping ephemeris; the order in which source files are specified determines the precedence when source files contain overlapping data.

SPKMERGE reads all its instructions from a command file. A command file is an ASCII formatted file containing `KEYWORD = value' assignments.



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Running SPKMERGE



SPKMERGE will prompt for the name of the command file when you start the program. Alternately, you can name the command file as the only argument on the command line.



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Command file syntax



Instructions are specified in a command file using `KEYWORD = value' assignments. The rules for forming assignments are listed here.

    -- Up to 6000 assignments may be specified in a single command file. Each assignment can be up to 350 characters long.

    -- An assignment must start on a line by itself. A keyword must appear first, followed by an equals sign, followed by a value.

    -- Keywords are not case sensitive---they may appear in upper, lower, or mixed case.

    -- Spaces and tabs are ignored, except for those embedded within values.

    -- Values other than file names may extend over multiple lines. No continuation characters are necessary.

    -- File names provided as values can be up to 255 characters long.

    -- Values other than file names can be up to 300 characters long.

    -- A semi-colon signals the beginning of a comment. All characters following a semi-colon on a line are ignored.

In addition, there are other non-lexical rules that apply to assignments:

    -- Some assignments must be present in the command file, while others are optional.

    -- Most assignments can only follow certain other assignments.

    -- All assignments have restrictions on the number of times they can appear in the command file.

These rules will be discussed as the keywords are introduced.



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Command file keywords



A command file must contain at least these three keywords: 

   LEAPSECONDS_KERNEL
   SPK_KERNEL
   SOURCE_SPK_KERNEL
The `LEAPSECONDS_KERNEL' keyword must appear in the file before the first `SPK_KERNEL' keyword. An `SPK_KERNEL' keyword must appear before the first `SOURCE_SPK_KERNEL' keyword.

The optional keywords are: 

   LOG_FILE
   BODIES
   BEGIN_TIME
   END_TIME
   INCLUDE_COMMENTS
Normally keywords must appear in the following order: 

   LEAPSECONDS_KERNEL     = <LSK file name>          (required)
   SPK_KERNEL             = <output SPK name>        (required)
      LOG_FILE            = <log file name>             (optional)
      BODIES              = <body ID list>              (optional)
      BEGIN_TIME          = <begin time>                (optional)
      END_TIME            = <end time>                  (optional)
      ... more BEGIN_/END_TIME pairs can follow ...     (optional)
      SOURCE_SPK_KERNEL   = <source SPK name>        (required)
         INCLUDE_COMMENTS = <yes or no>                 (optional)
         BODIES           = <body ID list>              (optional)
         BEGIN_TIME       = <begin time>                (optional)
         END_TIME         = <end time>                  (optional)
         ... more BEGIN_/END_TIME pairs can follow ...  (optional)
      SOURCE_SPK_KERNEL   = <source SPK name>        (optional)
         INCLUDE_COMMENTS = <yes or no>                 (optional)
         BODIES           = <body ID list>              (optional)
         BEGIN_TIME       = <begin time>                (optional)
         END_TIME         = <end time>                  (optional)
      ... more SOURCE_SPK_KERNEL blocks can follow ...  (optional)
   SPK_KERNEL             = <output SPK name>        (optional)
      LOG_FILE            = <log file name>             (optional)
      BODIES              = <body ID list>              (optional)
      BEGIN_TIME          = <begin time>                (optional)
      END_TIME            = <end time>                  (optional)
      ... more BEGIN_/END_TIME pairs can follow ...     (optional)
      SOURCE_SPK_KERNEL   = <source SPK name>        (optional)
         INCLUDE_COMMENTS = <yes or no>                 (optional)
         BODIES           = <body ID list>              (optional)
         BEGIN_TIME       = <begin time>                (optional)
         END_TIME         = <end time>                  (optional)
         ... more BEGIN_/END_TIME pairs can follow ...  (optional)
      ... more SOURCE_SPK_KERNEL blocks can follow ...  (optional)
   ... more SPK_KERNEL blocks can follow ...            (optional)
All the keywords are described in detail below.



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LEAPSECONDS_KERNEL



The value of this keyword must be the name of a SPICE leapseconds kernel file. This assignment must be present and must be the first assignment in the command file. If the leapseconds kernel does not reside in the current directory, remember to include the directory path of the file, as shown in this example: 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls


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SPK_KERNEL



The value of this keyword must be the name of the SPK file that SPKMERGE is to create. After this assignment, the names of one or more source SPK files must be listed by using the `SOURCE_SPK_KERNEL' assignment.

Multiple SPK files (up to 1000) can be created by SPKMERGE by repeating the `SPK_KERNEL' assignment.



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SOURCE_SPK_KERNEL



The value of this keyword must be the name of an existing SPK file that you want to merge into an output SPK file. Multiple SPK files or different parts of a single SPK file can be merged into an output SPK file by repeating this assignment. It can be repeated up to 1000 times for each output SPK file. Before you name the files you want to merge, you must have previously specified the name of an output SPK kernel by using the `SPK_KERNEL' assignment.

The sample command file below instructs SPKMERGE to create one SPK file by merging three existing SPK files in their entirety. 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     SOURCE_SPK_KERNEL = planets.bsp
     SOURCE_SPK_KERNEL = gll_1.bsp
     SOURCE_SPK_KERNEL = gll_2.bsp
SPKMERGE will not create an SPK file that has overlapping data. The files you list first have precedence. (Caution: this is the opposite of the precedence rules used elsewhere in SPICE!) In the example above, source data from planets.bsp will have precedence over data from gll_1.bsp, and both will have precedence over gll_2.bsp.



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BODIES



This keyword is optional. If present, it restricts which bodies are merged. This keyword can appear in one of two places: after a `SOURCE_SPK_KERNEL' assignment, or before the first `SOURCE_SPK_KERNEL' assignment. In the former case, the keyword lists the bodies that should be merged from a specific source SPK file; in the latter case, the keyword lists the bodies that should be merged from all source SPK files that do not have specific bodies mentioned. This keyword may appear only once for each output or source SPK file. A body listed in this assignment does not have to be contained within the source SPK file(s) the assignment applies to. Remember that SPKMERGE will not create a file that has overlapping data, so even if an SPK kernel contains a body you list, it may not necessarily be merged.

The bodies must be given as NAIF integer body IDs; the IDs may be delimited by spaces or commas.

In the example below, only data for bodies 10, 399 and 301 will be merged from `planets.bsp'. The other two files will be merged in their entirety---assuming no overlapping data. 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     SOURCE_SPK_KERNEL = planets.bsp
       BODIES          = 10, 399, 301
     SOURCE_SPK_KERNEL = gll_1.bsp
     SOURCE_SPK_KERNEL = gll_2.bsp
If you want to merge only data for bodies 10, 399, 301 and -77, from each of the three source files the command file could be structured as shown below: 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     BODIES            = 10, 399, 301, -77
     SOURCE_SPK_KERNEL = planets.bsp
     SOURCE_SPK_KERNEL = gll_1.bsp
     SOURCE_SPK_KERNEL = gll_2.bsp


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BEGIN_TIME, END_TIME



These two keywords operate just like the `BODIES' keyword, except they restrict times instead of bodies. The `END_TIME' keyword must immediately follow the `BEGIN_TIME' keyword. Together, these keywords represent a time window. Multiple windows (up to 1000) can be specified by repeating these two assignments.

SPKMERGE accepts many different time input formats from a variety of time systems. The default input system is UTC, but one may specify ephemeris time (TDB) instead. For complete details on the accepted time strings see the STR2ET section of ``Time Required Reading'' (time.req). Below are a few examples.

The following illustrates utilization of the default time system, UTC. 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     SOURCE_SPK_KERNEL = planets.bsp
       BEGIN_TIME      = 1 JAN 1994 00:00:00.000
       END_TIME        = 1 JUL 1994 00:00:00.000
     SOURCE_SPK_KERNEL = gll_1.bsp
       BEGIN_TIME      = 1 JAN 1994 00:00:00.000
       END_TIME        = 1 JUL 1994 00:00:00.000
     SOURCE_SPK_KERNEL = gll_2.bsp
       BEGIN_TIME      = 1 JAN 1994 00:00:00.000
       END_TIME        = 1 JUL 1994 00:00:00.000
To select ephemeris time (ET, also called Barycentric Dynamical Time or TDB) as the desired input time system, append TDB to the end of the time string. The following example demonstrates the merging of the contents of two SPK files for the period between the ephemeris times `15 Feb 1998' and `21 Jul 1998'. 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     SOURCE_SPK_KERNEL = planets.bsp
       BEGIN_TIME      = 15 FEB 1998 00:00:00.000 TDB
       END_TIME        = 21 JUL 1998 00:00:00.000 TDB
     SOURCE_SPK_KERNEL = mgs_ab2.bsp
       BEGIN_TIME      = 15 FEB 1998 00:00:00.000 TDB
       END_TIME        = 21 JUL 1998 00:00:00.000 TDB
In the following example SPKMERGE is instructed to merge only the UTC times `1 Jan 1994' through `2 Jan 1994'. Since no `BODIES' keyword is given, all bodies will be merged. In this example a command log file is also produced (see explanation below). 

   LEAPSECONDS_KERNEL  = /kernels/gen/lsk/naif0010.tls
 
   SPK_KERNEL          = complete.bsp
     LOG_FILE          = gll_early_cruise.log
     BEGIN_TIME        = 1 JAN 1994 00:00:00.000
     END_TIME          = 1 JUL 1994 00:00:00.000
     SOURCE_SPK_KERNEL = planets.bsp
     SOURCE_SPK_KERNEL = gll_1.bsp
     SOURCE_SPK_KERNEL = gll_2.bsp


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LOG_FILE



If this keyword is present it instructs SPKMERGE to create a log file. This keyword can only follow an `SPK_KERNEL' assignment and can appear only once for each output SPK file. A log file created by SPKMERGE will contain a list of all the SPK files that were used to create an SPK file, including all the times and all the bodies. The log file will be in the form of a command file, so it can be used as such if the need arises. An exact copy of the log file is always placed in the comment area of an SPK file created by SPKMERGE. The value field for this assignment can be any file name that is valid on the computer being used.



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INCLUDE_COMMENTS



If this keyword is present it can only have a value of YES or NO (upper or lower case), and it can only follow a `SOURCE_SPK_KERNEL' assignment and appear only once for each source SPK file. If the value of this keyword is YES, the comment area of the source SPK file named prior to this assignment is merged into the new SPK file, otherwise it is not. The default action is to not merge the comment area of a source SPK file.