SPKMERGE User's Guide

Index Page 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
Top # SPKMERGE User's Guide Last revised on 2001 APR 03 by F. S. Turner, C. H. Acton. Top ## Abstract SPKMERGE is a program that subsets or merges one or more SPK files into a single SPK file. Top ## 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 input from a command file. A command file is an ASCII formatted file that you must supply. Top ## 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 first argument on the command line. Top ## Command file syntax Inputs are specified in a command file by using assignments. The rules for forming assignments are listed here. `--` 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 may extend over multiple lines. No continuation characters are necessary. `--` A semi-colon signals the beginning of a comment. All characters following a semi-colon on a line are ignored. `--` Values must not exceed 300 characters. 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. Top ## Command file keywords A command file must contain at least these three keywords:
       LEAPSECONDS_KERNEL
       SPK_KERNEL
       SOURCE_SPK_KERNEL
The optional keywords are:
       LOG_FILE
       BEGIN_TIME
       END_TIME
       BODIES
       INCLUDE_COMMENTS
All the keywords are described below. Note that some keywords may appear multiple times. Top ### leapseconds_kernel The value of this keyword must be the name of a SPICE leapseconds kernel file. This assignment must be present, and is usually 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/lsk/naif0004.tls
Top ### 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 can be created by SPKMERGE by repeating this assignment. Top ### source_spk_kernel The value of this keyword must be the name of an existing SPK file that you want to merge into a new SPK file. Multiple SPK files or different parts of a single SPK file can be merged into a new SPK file by repeating this assignment. Before you name the files you want to merge, you must have previously specified the name of a new 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/lsk/naif0003.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. 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. Top ### 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' assignemt. 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. 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 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/lsk/naif0003.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 bodies 10, 399, 301 and -77, the command file could be structured as shown below:
       leapseconds_kernel  = /kernels/lsk/naif0003.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
Top ### 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 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/lsk/naif0003.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 Time Dynamic Barycentric 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' amd `21 Jul 1998'.
       leapseconds_kernel  = /kernels/lsk/naif0003.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/lsk/naif0003.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
Top ### log_file If this keyword is present it instructs SPKMERGE to create a log file. This keyword can only follow an `spk_kernel' assignment. 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. Top ### 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. 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 not to merge the comment area of a source SPK file.