 
Preface - Other Stuff (The Red Shirt topics) (C)
===========================================================================
 
   October 20, 2008
 
   The extensive scope of the CSPICE system's functionality includes
   features the average user may not expect or appreciate, features NAIF
   refers to as "Other Stuff." This workbook includes a set of lessons to
   introduce the beginning to moderate user to such features.
 
   The lessons provide a brief description to several related sets of
   routines, associated reference documents, a programming task designed to
   teach the use of the routines, and an example solution to the
   programming problem.
 
 
Coding and Use Lessons
===========================================================================
 
   This workbook contains lessons to demonstrate use of the less celebrated
   CSPICE routines.
 
       1.   Kernel Management with the Kernel Subsystem
 
       2.   The Kernel Pool
 
       3.   Coordinate Conversions
 
       4.   Advanced Time Manipulation Routines
 
       5.   Error Handling
 
       6.   Windows and Cells
 
       7.   Utility and Constants Routines
 
 
Note About HTML Links
--------------------------------------------------------
 
   The HTML version of this lesson contains links pointing to various HTML
   documents provided with the Toolkit. All of these links are relative
   and, in order to function, require this document to be in a certain
   location in the Toolkit HTML documentation directory tree.
 
   In order for the links to be resolved, create a subdirectory called
   ``lessons'' under the ``doc/html'' directory of the Toolkit tree and
   copy this document to that subdirectory before loading it into a Web
   browser.
 
 
NAIF Documentation
--------------------------------------------------------
 
   The technical complexity of the various CSPICE subsystems mandates an
   extensive, user-friendly documentation set. The set differs somewhat
   depending on your choice of development language, FORTRAN, C, IDL, or
   MATLAB but provides the same information with regards to SPICE
   operation.
 
   The sources for a user needing information concerning the CSPICE System
   or other NAIF product:
 
       --   Required Readings and Users Guides
 
       --   Library Source Code Documentation
 
       --   API Documentation
 
       --   Tutorials
 
 
Required Reading and Users Guides
 
   NAIF Required Reading (*.req) documents introduce the functionality of
   particular CSPICE subsystems:
 
 
      cells.req
      ck.req
      cspice.req
      daf.req
      das.req
      ek.req
      ellipses.req
      error.req
      frames.req
      icy.req
      intrdctn.req
      kernel.req
      mice.req
      naif_ids.req
      pck.req
      planes.req
      problems.req
      rotation.req
      scanning.req
      sclk.req
      sets.req
      spc.req
      spk.req
      symbols.req
      time.req
      windows.req
 
 
   NAIF Users Guides (*.ug) describe the proper use of particular CSPICE
   tools:
 
 
      brief.ug
      chronos.ug
      ckbrief.ug
      commnt.ug
      convert.ug
      inspekt.ug
      mkspk.ug
      msopck.ug
      simple.ug
      spacit.ug
      spkdiff.ug
      spkmerge.ug
      states.ug
      subpt.ug
      tictoc.ug
      tobin.ug
      toxfr.ug
      version.ug
 
 
   These text documents exist in the 'doc' directory of the main Toolkit
   directory:
 
         ../cspice/doc/
 
   HTML format documentation
 
   The CSPICE distributions include HTML versions of Required Readings and
   Users Guides, accessible from the HTML documentation directory:
 
         ../cspice/doc/html/index.html
 
 
Library Source Code Documentation
 
   All SPICELIB and CSPICE source files include usage and design
   information incorporated in a comment block known as the "header."
   (Every toolkit includes either the SPICELIB or CSPICE library.)
 
   A header consists of several marked sections:
 
       --   Procedure: Routine name and one line expansion of the routine's
            name.
 
       --   Abstract: A tersely worded explanation describing the routine.
 
       --   Copyright: An identification of the copyright holder for the
            routine.
 
       --   Required_Reading: A list of CSPICE required reading documents
            relating to the routine.
 
       --   Brief_I/O: A table of arguments, identifying each as either
            input, output, or both, with a very brief description of the
            variable.
 
       --   Detailed_Input & Detailed_Output: An elaboration of the
            Brief_I/O section providing comprehensive information on
            argument use.
 
       --   Parameters: Description and declaration of any parameters
            (constants) specific to the routine.
 
       --   Exceptions: A list of error conditions the routine detects and
            signals plus a discussion of any other exceptional conditions
            the routine may encounter.
 
       --   Files: A list of other files needed for the routine to operate.
 
       --   Particulars: A discussion of the routine's function (if
            needed). This section may also include information relating to
            "how" and "why" the routine performs an operation and to
            explain functionality of routines that operate by side effects.
 
       --   Examples: Descriptions and code snippets concerning usage of
            the routine.
 
       --   Restrictions: Restrictions or warnings concerning use.
 
       --   Literature_References: A list of sources required to understand
            the algorithms or data used in the routine.
 
       --   Author_and_Institution: The names and affiliations for authors
            of the routine.
 
       --   Version: A list of edits and the authors of those edits made to
            the routine since initial delivery to the CSPICE system.
 
   The source code for CSPICE products is stored in 'src' sub-directory of
   the main CSPICE directory:
 
         ../cspice/src/
 
   Find the CSPICE library source code in:
 
         ../cspice/src/cspice/
 
   Note: The CSPICE source files have two forms: C files created by the f2c
   conversion process on a SPICELIB files, indicated with a name of the
   form "module.c," and wrappers files indicated by names of the form
   "module_c.c" The f2c converted source code is very difficult to read,
   refer to the wrapper routines if possible. In some cases, NAIF replaced
   an f2c converted file with a hand written version.
 
 
API Documentation
 
   The CSPICE package includes the CSPICE Reference Guide, an index of all
   CSPICE wrapper APIs with hyperlinks to API specific documentation. Each
   API documentation page includes cross-links to any other wrapper API
   mentioned in the document and links to the wrapper source code.
 
         ...cspice/doc/html/cspice/index.html
 
 
Tutorials
 
   A set of Microsoft PowerPoint presentations provide a general overview
   of the complete CSPICE toolkit. Download the set at:
 
         http://naif.jpl.nasa.gov/naif/tutorials.html
 
   Access individual files in the 'office/individual_docs/' directory; an
   archive of all tutorial files is available in the 'office/packages/'
   directory.
 
 
Text kernels
--------------------------------------------------------
 
   Several workbooks use SPICE text kernels. SPICE identifies a text kernel
   as an ASCII text file containing the mark-up tags the kernel subsystem
   requires to identify data assignments in that file, and "name=value"
   data assignments.
 
   The subsystem uses two tags:
 
         \begintext
 
   and
 
         \begindata
 
   to mark information blocks within the text kernel. The \begintext tag
   specifies all text following the tag as comment information to be
   ignored by the subsystem.
 
   Things to know:
 
       1.   The \begindata tag marks the start of a data definition block.
            The subsystem processes all text following this marker as SPICE
            kernel data assignments until finding a \begintext marker.
 
       2.   The kernel subsystem defaults to the \begintext mode until the
            parser encounters a \begindata tag. Once in \begindata mode the
            subsystem processes all text as variable assignments until the
            next \begintext tag.
 
       3.   Enter the tags as the only text on a line, i.e.:
 
 
         \begintext
 
            ... commentary information on the data assignments ...
 
         \begindata
 
            ... data assignments ...
 
 
       4.   CSPICE delivery N0059 added to the CSPICE and Icy text kernel
            parsers the functionality to read non native text kernels, i.e.
            a Unix compiled library can read a MS Windows native text
            kernel, a MS Windows compiled library can read a Unix native
            text kernel. Mice acquires this capability from CSPICE.
 
       5.   With regards to the FORTRAN distribution, as of delivery N0057
            the FURNSH call includes a line terminator check, signaling an
            error on any attempt to read non-native text kernels.
 
 
Text kernel format
 
   Scalar assignments.
 
         VAR_NAME_DP  = 1.234
         VAR_NAME_INT = 1234
         VAR_NAME_STR = 'FORBIN'
 
   Please note the use of a single quote in string assignments.
 
   Vector assignments. Vectors must contain the same type data.
 
         VEC_NAME_DP  = ( 1.234   , 45.678  , 901234.5 )
         VEC_NAME_INT = ( 1234    , 456     , 789      )
         VEC_NAME_STR = ( 'FORBIN', 'FALKEN', 'ROBUR'  )
 
         also
 
         VEC_NAME_DP  = ( 1.234,
                         45.678,
                         901234.5 )
 
         VEC_NAME_STR = ( 'FORBIN',
                          'FALKEN',
                          'ROBUR' )
 
   Time assignments.
 
         TIME_VAL = @31-JAN-2003-12:34:56.798
         TIME_VEC = ( @01-DEC-2004, @15-MAR-2004 )
 
   The at-sign character '@' indicates a time string. The pool subsystem
   converts the strings to double precision TDB (a numeric value). Please
   note, the time strings must not contain embedded blanks. WARNING - a TDB
   string is not the same as a UTC string.
 
   The above examples depict direct assignments via the '=' operator. The
   kernel pool also permits incremental assignments via the '+=' operator.
 
   Please refer to the kernels required reading, kernel.req, for additional
   information.
 
 
Kernels for lessons
--------------------------------------------------------
 
 
Input kernel files
 
   The following kernels are used in examples provided in these lessons:
 
         FILE NAME                TYPE  DESCRIPTION
         -----------------------  ----  ----------------------
         naif0008.tls             LSK   Generic LSK
         leapseconds.tls          LSK   The current leapseconds
                                        kernel (naif0008.tls as
                                        of Jan 2006)
         de405s.bsp               SPK   Planet Ephemeris SPK
         pck00008.tpc             PCK   Generic PCK
 
   These SPICE kernels are included in the lesson package available from
   the NAIF server at JPL:
 
      ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Lessons/
 
 
Output
 
   The code examples listed in this workbook include corresponding outputs
   for the described inputs. The output of a given example on a particular
   platform may not exactly match that shown since compilers and math
   libraries differ between platform architectures.
 
 
Lesson 1: Kernel Management with the Kernel Subsystem
===========================================================================
 
   Lesson Goals:
 
   This lesson demonstrates use of the kernel subsystem to load, unload,
   and list loaded kernels.
 
   This lesson requires creation of a SPICE meta kernel.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   furnsh_c loads the meta kernel and the SPICE kernels listed
            within that kernel.
 
       --   ktotal_c retrieves the number of SPICE kernels loaded by the
            kernel subsystem.
 
       --   kdata_c returns information about each loaded kernel.
 
       --   unload_c removes a kernel and deletes any pool variables
            defined by that kernel from the kernel subsystem.
 
       --   kclear_c deletes all kernel pool data from the kernel
            subsystem.
 
 
Requirements and References
--------------------------------------------------------
 
   Knowledge of information in the kernels.req document, the mk.ppt and
   intro_to_kernels.ppt tutorial files.
 
 
Programming Task
--------------------------------------------------------
 
   Write a program to load a meta kernel, interrogate the CSPICE system for
   the names and types of all loaded kernels, then demonstrate the unload
   functionality and the resulting effects.
 
 
Code Solution
--------------------------------------------------------
 
 
First, create a meta text kernel:
 
   You can use two versions of a meta kernel with code examples (meta.tm)
   in this lesson. Either a kernel with explicit path information:
 
 
      \begindata
 
         KERNELS_TO_LOAD = ( 'kernels/spk/de405s.bsp',
                             'kernels/pck/pck00008.tpc',
                             'kernels/lsk/leapseconds.tls')
 
      \begintext
 
 
   ... or a more generic meta kernel using the PATH_VALUES/PATH_SYMBOLS
   functionality to declare path names as variables:
 
 
      \begintext
 
      Define the paths to the kernel directory. Use the PATH_SYMBOLS
      as aliases to the paths.
 
      \begindata
 
         PATH_VALUES     = ( 'kernels/lsk',
                             'kernels/spk',
                             'kernels/pck' )
 
         PATH_SYMBOLS    = ( 'LSK', 'SPK', 'PCK' )
 
         KERNELS_TO_LOAD = ( '$LSK/naif0008.tls',
                             '$SPK/de405s.bsp',
                             '$PCK/pck00008.tpc' )
 
      \begintext
 
 
 
Now the solution source code:
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /*
      Define the maximum length for any string, 80
      characters plus one null terminator.
      */
      #define LENOUT 81
 
      int main( int argc, char **argv )
         {
 
         /*  Declare the needed variables: */
 
         SpiceChar     file   [LENOUT];
         SpiceChar     type   [LENOUT];
         SpiceChar     source [LENOUT];
 
         SpiceInt      i;
         SpiceInt      count;
         SpiceInt      handle;
 
         SpiceBoolean  found;
 
 
         /* Assign the path name of the meta kernel to META. */
         SpiceChar   * META = "meta.tm";
 
 
         /*
         Load the meta kernel then use KTOTAL to interrogate the SPICE
         kernel subsystem for the total number of loaded kernel files.
         */
         furnsh_c ( META );
         ktotal_c ("ALL", &count );
         printf( "Kernel count after load: %ld\n", count );
 
 
         /*
         Loop over the number of files; interrogate the SPICE system
         with kdata_c for the kernel names and the type. 'found' returns a
         boolean indicating whether any kernel files of the specified
         type were loaded by the kernel subsystem. This example ignores
         checking 'found' as kernels are known to be loaded.
         */
         for (i = 0L; i < count; i++ )
           {
            kdata_c( i, "ALL", LENOUT, LENOUT, LENOUT,
                         file, type, source, &handle, &found );
            printf ( "File %s\n", file );
            printf ( "Type %s\n", type );
            printf ( "Source %s\n", source );
            printf ( "\n" );
           }
 
 
         /*
         Unload one kernel then check the count.
         */
         unload_c ( "kernels/spk/de405s.bsp" );
         ktotal_c ( "ALL", &count );
 
 
         /*
         The subsystem should report one less kernel.
         */
         printf ( "Kernel count after one unload: %ld\n", count );
 
 
         /*
         Now unload the meta kernel. This action unloads all
         files listed in the meta kernel.
         */
         unload_c ( META );
 
 
         /*
         Check the count. SPICE should return a count of zero.
         */
         ktotal_c ( "ALL", &count );
         printf ( "Kernel count after meta unload: %ld\n", count );
 
         exit(0);
         }
 
 
 
Run the code example
 
   First we see the number of all loaded kernels returned from the ktotal_c
   call:
 
 
       Kernel count after load:   4
 
 
   Now the kdata_c loop returns the name of each loaded kernel, the type of
   kernel (SPK, CK, TEXT, etc.) and the source of the kernel - the
   mechanism that loaded the kernel. The source either identifies a meta
   kernel, or contains an empty string. An empty source string indicates a
   direct load of the kernel with a furnsh_c call.
 
 
      File   meta.tm
      Type   META
      Source
 
      File   kernels/spk/de405s.bsp
      Type   SPK
      Source meta.tm
 
      File   kernels/pck/pck00008.tpc
      Type   TEXT
      Source meta.tm
 
      File   kernels/lsk/naif0008.tls
      Type   TEXT
      Source meta.tm
 
      Kernel count after one unload :   3
      Kernel count after meta unload:   0
 
 
 
Lesson 2: The Kernel Pool
===========================================================================
 
   Lesson Goals:
 
   The lesson demonstrates the CSPICE system's facility to retrieve
   different types of data (string, numeric, scalar, array) from the kernel
   pool.
 
   For the code examples, use this generic text kernel (cassini.tm)
   containing PCK-type data, kernels to load, and example time strings:
 
      \begintext
 
      Ring model data.
 
      \begindata
 
         BODY699_RING1_NAME     = 'A Ring'
         BODY699_RING1          = (122170.0 136780.0 0.1 0.1 0.5)
 
         BODY699_RING1_1_NAME   = 'Encke Gap'
         BODY699_RING1_1        = (133405.0 133730.0 0.0 0.0 0.0)
 
         BODY699_RING2_NAME     = 'Cassini Division'
         BODY699_RING2          = (117580.0 122170.0 0.0 0.0 0.0)
 
      \begintext
 
      The kernel pool recognizes values preceded by '@' as time
      values. When read, the kernel subsystem converts these
      representations into double precision ephemeris time.
 
      Caution: The kernel subsystem interprets the time strings
      identified by '@' as TDB. The same string passed as input
      to @STR2ET is processed as UTC.
 
      The three expressions stored in the EXAMPLE_TIMES array represent
      the same epoch.
 
      \begindata
 
         EXAMPLE_TIMES       = ( @APRIL-1-2004-12:34:56.789,
                                 @4/1/2004-12:34:56.789,
                                 @JD2453097.0242684
                                )
 
      \begintext
 
      Name the kernels to load. Use path symbols.
 
      \begindata
 
         PATH_VALUES     = ('kernels/spk',
                            'kernels/pck',
                            'kernels/lsk')
 
         PATH_SYMBOLS    = ('SPK' , 'PCK' , 'LSK' )
 
         KERNELS_TO_LOAD = ( '$SPK/de405s.bsp',
                             '$PCK/pck00008.tpc',
                             '$LSK/leapseconds.tls')
 
      \begintext
 
 
Relevant Routines
--------------------------------------------------------
 
       --   gipool_c retrieves integer values from the kernel subsystem.
 
       --   gdpool_c retrieves double precision values from the kernel
            subsystem
 
       --   gcpool_c retrieves character values from the kernel subsystem
 
       --   dtpool_c returns data (name, type, size) describing a kernel
            pool variable.
 
       --   gnpool_c retrieves the names of kernel pool variables matching
            a given template.
 
 
Requirements and References
--------------------------------------------------------
 
   Knowledge of the material in the kernels.req document and the
   intro_to_kernels.ppt tutorial file.
 
   The main references for pool routines are found in the source files or
   API documentation for the particular routines.
 
 
Programming Task
--------------------------------------------------------
 
   Write a program to retrieve particular string and numeric text kernel
   variables, both scalars and arrays. Interrogate the kernel pool for
   assigned variable names.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /*
      Define the max number of kernel variables
      of concern for this examples.
      */
      #define N_ITEMS   20
 
      /*
      Define the maximum length for any string, 80
      characters plus one null terminator.
      */
      #define STRLEN 81
 
      int main( int argc, char **argv )
         {
 
         /*
         Note, the pool routines return a boolean to 'found'
         signaling whether the requested variable name exists
         in the kernel pool. The code solutions do not check the
         boolean value since the solutions use variables known to
         exist. In general, code should always check the boolean
         value to ensure return of valid data.
         */
 
         /*
         As usual, type our variables...
         */
         SpiceInt                    i;
         SpiceInt                    j;
         SpiceInt                    dim;
         SpiceInt                    n_var;
         SpiceInt                    n_val;
         SpiceInt                    start;
 
         SpiceBoolean                found;
 
         SpiceDouble                 dvars    [N_ITEMS];
 
         SpiceChar                   cvals    [N_ITEMS][STRLEN];
         SpiceChar                   cvars    [N_ITEMS][STRLEN];
         SpiceChar                   type;
         SpiceChar                   tmplate[12];
 
 
         /*
         Load the example kernel containing the kernel variables.
         The kernels defined in KERNELS_TO_LOAD load into the
         kernel pool with this call.
         */
         furnsh_c ( "cassini.tm" );
 
         /*
         Initialize the start value. This values indicates
         index of the first element to return if a kernel
         variable is an array. start = 0 indicates return everything.
         start = 1 indicates return everything but the first element.
         */
         start = 0;
 
 
         /*
         Set the template for the variable names to find. Let's
         look for all variables containing  the string RING.
         Define this with the wildcard template '*RING*'. Note:
         the template '*RING' would match any variable name
         ending with the RING string.
         */
         strcpy ( tmplate, "*RING*");
 
         /*
         We're ready to interrogate the kernel pool for the
         variables matching the template. gnpool_c tells us:
 
            1. Does the kernel pool contain any variables that
               match the template (value of found).
            2. If so, how many variables? (value of n_val)
            3. The variable names. (cvals, an array of strings)
         */
 
         gnpool_c ( tmplate, start, N_ITEMS, STRLEN,
                    &n_val, cvals, &found );
 
         if ( found )
            {
            printf( "No. variables matching template: %ld\n", n_val);
            }
         else
            {
            puts ( "No kernel variables matched template" );
            exit(0);
            }
 
 
         /*
         Okay, now we know something about the kernel pool
         variables of interest to us. Let's find out more...
         */
         for (i=0; i<n_val; ++i )
            {
 
            /*
            Use dtpool_c to return the dimension and type,
            C (character) or N (numeric), of each pool
            variable name in the cvals array.
            */
            dtpool_c ( cvals[i], &found, &dim, &type );
            printf ( "\n%s\n", cvals[i]);
            printf ( "No. items: %ld Of type: %c\n\n", dim, type );
 
            /*
            Use the EQSTR routine to test character equality,
            'N' or 'C'.
            */
            if ( type == 'N' )
               {
 
               /*
               If 'type' equals "N", we found a numeric array.
               In this case any numeric array will be an array
               of double precision numbers ("doubles"). gdpool_c
               retrieves doubles from the kernel pool. 'dvars'
               contains the array of 'n_vars' values.
               */
               gdpool_c ( cvals[i], start, N_ITEMS, &n_var,
                                           dvars  , &found );
 
               for( j=0; j<n_var; ++j )
                  {
                  printf( "  Numeric value: %f\n", dvars[j] );
                  }
 
               }
            else if ( type == 'C' )
               {
 
               /*
               If 'type' equals "C", we found a string array.
               gcpool_c retrieves string values from the
               kernel pool. cvars[i] contains the array of 'n_var'
               values.
               */
               gcpool_c ( cvals[i], start , N_ITEMS,
                          STRLEN  , &n_var, cvars  , &found );
 
               for( j=0; j<n_var; ++j )
                  {
                  printf( "  String value: %s\n", cvars[j] );
                  }
 
               }
 
            }
 
         puts( " " );
 
         /*
         Now look at the kernel variable EXAMPLE_TIMES. Extract this
         value as an array of doubles.
         */
         gdpool_c ( "EXAMPLE_TIMES", start, N_ITEMS, &n_var, dvars,
                    &found );
 
         puts( "EXAMPLE_TIMES");
 
         for( j=0; j<n_var; ++j )
            {
            printf( "  Time value: %f\n", dvars[j] );
            }
 
         exit(0);
         }
 
 
 
Run the code example
 
   The program runs and first reports the number of kernel pool variables
   matching the template, 6.
 
 
      No. variables matching template:   6
 
 
   The program then loops over the dtpool_c 6 times, reporting the name of
   each pool variable, the number of data items assigned to that variable,
   and the variable type. Within the dtpool_c loop, a second loop outputs
   the contents of the data variable using gcpool_c or gdpool_c.
 
 
      BODY699_RING1
       No. items: 5 Of type: N
 
        Numeric value: 122170.000000
        Numeric value: 136780.000000
        Numeric value: 0.100000
        Numeric value: 0.100000
        Numeric value: 0.500000
 
      BODY699_RING2
       No. items: 5 Of type: N
 
        Numeric value: 117580.000000
        Numeric value: 122170.000000
        Numeric value: 0.000000
        Numeric value: 0.000000
        Numeric value: 0.000000
 
      BODY699_RING1_1
       No. items: 5 Of type: N
 
        Numeric value: 133405.000000
        Numeric value: 133730.000000
        Numeric value: 0.000000
        Numeric value: 0.000000
        Numeric value: 0.000000
 
      BODY699_RING1_NAME
       No. items: 1 Of type: C
 
        String value: A Ring
 
      BODY699_RING2_NAME
       No. items: 1 Of type: C
 
        String value: Cassini Division
 
      BODY699_RING1_1_NAME
       No. items: 1 Of type: C
 
        String value: Encke Gap
 
 
   Note the final time value differs from the previous values in the final
   three decimal places despite the intention that all three strings
   represent the same time. This results from round-off when converting a
   decimal Julian day representation to the seconds past J2000 ET
   representation.
 
 
      EXAMPLE_TIMES
        Time value: 134094896.789000
        Time value: 134094896.789000
        Time value: 134094896.789753
 
 
 
Lesson 3: Coordinate Conversions
===========================================================================
 
   Lesson Goals:
 
   The CSPICE system provides functions to convert coordinate tuples
   between Cartesian and various non Cartesian coordinate systems including
   conversion between geodetic and rectangular coordinates.
 
   This lesson presents these coordinate transform routines for
   rectangular, cylindrical, and spherical systems.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   latrec_c, latitudinal to rectangular
 
       --   latcyl_c, latitudinal to cylindrical
 
       --   latsph_c, latitudinal to spherical
 
       --   reccyl_c, rectangular to cylindrical
 
       --   recgeo_c, rectangular to geodetic
 
       --   reclat_c, rectangular to latitudinal
 
       --   recsph_c, rectangular to spherical
 
       --   recrad_c, rectangular to right ascension - declination
 
       --   sphrec_c, spherical to rectangular
 
       --   sphcyl_c, spherical to cylindrical
 
       --   sphlat_c, spherical to latitudinal
 
       --   cyllat_c, cylindrical to latitudinal
 
       --   cylsph_c, cylindrical to spherical
 
       --   cylrec_c, cylindrical to rectangular
 
       --   georec_c, geodetic to rectangular
 
 
Requirements and References
--------------------------------------------------------
 
   Basic knowledge of the standard coordinate systems used in celestial
   mechanics. The contents of concepts.ppt and derived_quant.ppt tutorial
   files.
 
 
Programming Task
--------------------------------------------------------
 
   Write a program to convert a Cartesian 3-vector representing some
   location to the other coordinate representations. Use the position of
   the Moon with respect to Earth in an inertial and non-inertial reference
   frame as the example vector.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /* Define the length of the time string, 32
      characters plus 1 for the null terminator.
      */
      #define LENOUT 33
 
      int main( int argc, char **argv )
         {
 
         /*
         Type the variables.
         */
         SpiceInt              dim;
 
         /*
         Define the inertial and non inertial frame names.
         */
         SpiceChar             inrfrm  [] = "J2000";
         SpiceChar             nonfrm  [] = "IAU_EARTH";
         SpiceChar             timstr  [LENOUT];
 
         SpiceDouble           et;
         SpiceDouble           range;
         SpiceDouble           ra;
         SpiceDouble           dec;
         SpiceDouble           lat;
         SpiceDouble           colat;
         SpiceDouble           lon;
         SpiceDouble           ltime;
         SpiceDouble           flat;
         SpiceDouble           rad   [3];
         SpiceDouble           pos   [3];
 
         /*
         Load the needed kernels using a furnsh_c call on the
         meta kernel.
         */
         furnsh_c ( "meta.tm" );
 
 
         /*
         Prompt the user for a time string. Convert the
         time string to ephemeris time J2000 (ET).
         */
         prompt_c ( "Time of interest: ", LENOUT, timstr );
         str2et_c ( timstr, &et );
 
         /*
         Access the kernel pool data for the triaxial radii of the
         Earth, 'rad[0]' holds the equatorial radius, 'rad[2]'
         the polar radius.
         */
         bodvrd_c ( "Earth", "RADII", 3, &dim, rad);
 
         /*
         Calculate the flattening factor for the Earth.
 
                  equatorial_radius - polar_radius
         flat =   ________________________________
 
                        equatorial_radius
         */
 
         flat = (rad[0] - rad[2])/rad[0];
 
         /*
         Make the spkpos_c call to determine the apparent position of
         the Moon w.r.t. to the Earth at 'et' in the inertial frame.
         */
         spkpos_c ( "MOON", et, inrfrm, "LT+S","EARTH", pos, &ltime);
 
 
         /*
         Show the current frame and time.
         */
         printf ( " Time : %s\n"         , timstr );
         printf ( "  Inertial Frame: %s\n", inrfrm );
 
         /*
         First convert the position vector
         X = pos[0], Y = pos[1], Z = pos[2], to RA/DEC.
         */
         recrad_c ( pos, &range, &ra, &dec );
         printf ( "   Range/Ra/Dec\n" );
         printf ( "    Range: %f\n", range        );
         printf ( "    RA   : %f\n", ra * dpr_c() );
         printf ( "    DEC  : %f\n", dec* dpr_c() );
 
         /*
         ...latitudinal coordinates...
         */
         reclat_c ( pos, &range, &lon, &lat );
         printf ( "   Latitudinal\n" );
         printf ( "    Rad  : %f\n", range);
         printf ( "    Lon  : %f\n", lon * dpr_c() );
         printf ( "    Lat  : %f\n", lat * dpr_c() );
 
         /*
         ...spherical coordinates use the colatitude,
         the angle from the Z axis.
         */
         recsph_c ( pos, &range, &colat, &lon );
         printf ( "   Spherical\n");
         printf ( "    Rad  : %f\n", range           );
         printf ( "    Lon  : %f\n", lon   * dpr_c() );
         printf ( "    Colat: %f\n", colat * dpr_c() );
 
 
         /*
         Make the spkpos_c call to determine the apparent position of
         the Moon w.r.t. to the Earth at 'et' in the non-inertial,
         body fixed, frame.
         */
         spkpos_c ( "MOON", et, nonfrm, "LT+S","EARTH", pos, &ltime);
 
         puts ( " " );
         printf ( "  Non-inertial Frame: %s\n", nonfrm );
 
         /*
         ...latitudinal coordinates...
         */
         reclat_c ( pos, &range, &lon, &lat );
         printf ( "   Latitudinal\n" );
         printf ( "    Rad  : %f\n", range         );
         printf ( "    Lon  : %f\n", lon * dpr_c() );
         printf ( "    Lat  : %f\n", lat * dpr_c() );
 
         /*
         ...spherical coordinates...
         */
         recsph_c ( pos, &range, &colat, &lon );
         printf ( "   Spherical\n" );
         printf ( "    Rad  : %f\n", range           );
         printf ( "    Lon  : %f\n", lon   * dpr_c() );
         printf ( "    Colat: %f\n", colat * dpr_c() );
 
         /*
         ...finally, convert the position to geodetic coordinates.
         */
         recgeo_c ( pos, rad[0], flat, &lon, &lat, &range );
         printf ( "   Geodetic\n" );
         printf ( "    Rad  : %f\n", range         );
         printf ( "    Lon  : %f\n", lon * dpr_c() );
         printf ( "    Lat  : %f\n", lat * dpr_c() );
         puts ( " " );
 
 
         exit(0);
         }
 
 
 
Run the code example
 
   Input a time/date at which to calculate the Moon's position. (the 'TDB'
   tag indicates a Barycentric Dynamical Time value).
 
 
      Time of interest: Feb 3 2002 TDB
 
 
   Examine the Moon position in the J2000 inertial frame, display the time
   and frame:
 
 
       Time : Feb 3 2002 TDB
        Inertial Frame: J2000
 
 
   Convert the Moon Cartesian coordinates to right ascension declination.
 
 
         Range/Ra/Dec
          Range: 369340.815193
          RA   : 203.643686
          DEC  : -4.979010
 
 
   Latitudinal. Note the difference in the expressions for longitude and
   right ascension though they represent a measure of the same quantity.
   The RA/DEC system measures RA in the interval [0,2Pi). Latitudinal
   coordinates measures longitude in the interval (-Pi,Pi].
 
 
         Latitudinal
          Rad  : 369340.815193
          Lon  : -156.356314
          Lat  : -4.979010
 
 
   Spherical. Note the difference between the expression of latitude in the
   Latitudinal system and the corresponding Spherical colatitude. The
   spherical coordinate system uses the colatitude, the angle measure away
   from the positive Z axis. Latitude is the angle between the position
   vector and the x-y (equatorial) plane with positive angle defined as
   toward the positive Z direction
 
 
         Spherical
          Rad  : 369340.815193
          Lon  : -156.356314
          Colat: 94.979010
 
 
   The same position look-up in a body fixed (non-inertial) frame,
   IAU_EARTH.
 
        Non-inertial Frame: IAU_EARTH
 
   Latitudinal coordinates return the geocentric latitude.
 
 
         Latitudinal
          Rad  : 369340.815193
          Lon  : 70.986950
          Lat  : -4.989675
 
 
   Spherical.
 
 
         Spherical
          Rad  : 369340.815193
          Lon  : 70.986950
          Colat: 94.989675
 
 
   Geodetic. The cartographic lat/lon.
 
 
         Geodetic
          Rad  : 362962.836755
          Lon  : 70.986950
          Lat  : -4.990249
 
 
 
Lesson 4: Advanced Time Manipulation Routines
===========================================================================
 
   Lesson Goals:
 
   Introduce the routines used for advanced manipulation of time strings.
   Understand the concept of ephemeris time (ET) as used in CSPICE.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   str2et_c converts time strings to ephemeris time (ET).
 
       --   timout_c formats a time string output.
 
       --   tpictr_c creates a format template for use in timout_c.
 
       --   tsetyr_c sets the reference century/year for two digit
            representation of the year.
 
 
Requirements and References
--------------------------------------------------------
 
   Knowledge of the time.req document, the time.ppt, lsk_and_sclk.ppt, and
   other_functions.ppt tutorial files.
 
   Also, examine the header of timout_c for a list of the string markers
   used by timout_c and tpictr_c to describe time string format. Always
   keep in mind str2et_c assumes 'UTC' unless indicated otherwise.
 
 
Programming Task
--------------------------------------------------------
 
   Demonstrate the advanced functions of the time utilities with regard to
   formatting of time strings for output. Formatting options include
   altering calendar representations of the time strings. Convert time-date
   strings between different CSPICE-supported formats.
 
 
Code Solution
--------------------------------------------------------
 
   Caution: Be sure to assign sufficient string lengths for time
   formats/pictures.
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /*
      Define the maximum length for any string, 80
      characters plus one null terminator.
      */
      #define STRLEN 256
 
      int main( int argc, char **argv )
         {
 
         /* Declare the needed variables: */
 
         SpiceDouble            et;
         SpiceDouble            et1;
         SpiceDouble            et2;
 
         SpiceBoolean           ok;
 
         SpiceChar              error [STRLEN];
         SpiceChar              pictr [STRLEN];
         SpiceChar              timstr[STRLEN];
 
         /*
         Assign the LSK variable to the name of the leapsecond,
         kernel and create an arbitrary time string.
         */
         SpiceChar            * CALSTR   =
                                "Mar 15, 2003 12:34:56.789 AM PST";
 
         SpiceChar            * LSK      =
                                "/kernels/gen/lsk/leapseconds.tls";
 
         SpiceChar            * AMBIGSTR =
                                "Mar 15, 79 12:34:56";
 
 
         /* Load the leapseconds kernel. */
 
         furnsh_c ( LSK );
         printf   ( "Original time string       : %s\n", CALSTR );
 
         /*
         Convert the time string to the number of ephemeris
         seconds past the J2000 epoch. This is the most common
         internal time representation used by the CSPICE
         system; CSPICE refers to this as ephemeris time (ET).
         */
         str2et_c ( CALSTR, &et );
         printf   ( "Corresponding ET           : %f\n", et     );
 
 
         /*
         Make a picture of an output format. Describe a Unix-like
         time string then send the picture and the 'et' value through
         timout_c to format and convert the ET representation of the
         time string into the form described in timout_c. The
         '::UTC-7' token indicates the time zone for the 'timstr'
         output - PDT. 'PDT' is part of the output, but not a time
         system token.
         */
         timout_c ( et,
                    "Wkd Mon DD HR:MN:SC PDT YYYY ::UTC-7",
                    STRLEN,
                    timstr );
         printf   ( "Time in string format 1    : %s\n", timstr );
 
 
         /*
         Create another picture, this time combine a calendar,
         2 digit year , with Julian Day format.
         */
         timout_c ( et,
                    "Wkd Mon DD HR:MN ::UTC-7 YR (JULIAND.##### JDUTC)",
                    STRLEN,
                    timstr );
         printf   ( "Time in string format 2    : %s\n", timstr );
 
 
         /*
         Why create a picture by hand when CSPICE can do it for you?
         Input a string to tpictr_c with the format of interest.
         'ok' returns a boolean indicating whether an error
         occurred while parsing the picture string, if so,
         an error diagnostic message returns in 'error'. In this
         example, no need exists to check the error flag since
         the picture string is known as correct..
         */
         tpictr_c ( "12:34:56.789 P.M. PDT January 1, 2006",
                    STRLEN,
                    STRLEN,
                    pictr,
                    &ok,
                    error);
 
         /*
         Confirm the tpictr_c call succeeded. Report the error string
         if not.
         */
         if( !ok )
            {
            printf( "\nError in TPICTR call:\n" );
            printf( "%s\n", error );
            exit(1);
            }
 
         timout_c ( et, pictr, STRLEN, timstr );
         printf   ("Time in string format 3    : %s\n", timstr );
 
 
         /*
         Two digit year representations often cause problems due to
         the ambiguity of the century. The routine tsetyr_c gives the
         user the ability to set a default range for 2 digit year
         representation. SPICE uses 1969AD as the default start
         year so the numbers inclusive of 69 to 99 represent years
         1969AD to 1999AD, the numbers inclusive of 00 to 68 represent
         years 2000AD to 2068AD.
 
         The defined time string AMBIGSTR contains a two-digit
         year. Since the SPICE base year is 1969, the time
         subsystem interprets the string as 1979.
         */
         str2et_c ( AMBIGSTR, &et1 );
 
 
         /*
         Set 1980 as the base year causes CSPICE to interpret the time
         string's "79" as 2079.
         */
         tsetyr_c ( 1980 );
         str2et_c ( AMBIGSTR, &et2 );
 
 
         /*
         Calculate the number of years between the two ET
         representations, ~100.
         */
         printf ( "Years between evaluations  : %f\n",
                               (et2 - et1)/jyear_c() );
 
         exit(0);
         }
 
 
 
Run the code example
 
 
      Original time string      : Mar 15, 2003 12:34:56.789 AM PST
      Corresponding ET          : 100989360.974561
      Time in string format 1   : Sat Mar 15 01:34:56 PDT 2003
      Time in string format 2   : Sat Mar 15 01:34 03 (2452713.85760 JDUTC)
      Time in string format 3   : 01:34:56.789 A.M. PDT March 15, 2003
      Years between evaluations : 100.000000
 
 
 
Lesson 5: Error Handling
===========================================================================
 
   Lesson Goal:
 
   This lesson introduces the basics of the error subsystem and its various
   the response modes: DEFAULT, RETURN, ABORT, RETURN, IGNORE, the error
   output modes: SHORT, LONG, EXPLAIN TRACEBACK, DEFAULT, ALL, NONE, and
   the error traceback message.
 
 
Relevant Routines:
--------------------------------------------------------
 
       --   failed_c returns TRUE if a CSPICE error signaled.
 
       --   reset_c resets the error subsystem to the state prior to an
            error signal - WARNING, this call resets only the error
            subsystem, the rest of the CSPICE system is unchanged.
 
       --   erract_c sets the reaction of the error subsystem to an error.
 
       --   errch_c inserts a character/string into an error message.
 
       --   errdp_c inserts a double precision value into an error message.
 
       --   errint_c inserts an integer value into an error message.
 
       --   errdev_c sets the device for error output.
 
       --   errprt_c sets the error message items for output on an error
            signal.
 
       --   sigerr_c signals a CSPICE error with a given short message.
 
       --   setmsg_c sets the long message corresponding to sigerr_c.
 
       --   return_c returns TRUE if a routine should return to caller on
            entry.
 
 
Requirements and References
--------------------------------------------------------
 
   Knowledge of material in the error.req document and the exceptions.ppt
   tutorial file. Comprehension of the catch/throw concept.
 
 
Programming Task
--------------------------------------------------------
 
   Show the behavior of the various error modes by writing a program to
   signal an error, check for an error signal, set the long and short error
   strings, set error behavior (DEFAULT, RETURN, ABORT, RETURN).
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /*
      Define the maximum length for any string, 80
      characters plus one null terminator.
      */
      #define STRLEN 81
 
      void doerr();
 
      int main( int argc, char **argv )
         {
 
         /*  Declare the needed variables: */
 
         SpiceChar      errcon[STRLEN];
         SpiceBoolean   doloop        = SPICETRUE;
 
         /*
         Check into the error subsystem to create a traceback
         showing the call tree. A chkout_c must balance every
         chkin_c.
         */
         chkin_c ( "ERRSYSC" );
 
         /*
         Before we start, what's the initial (default)
         error state? erract_c both sets the state and
         reports the state.
         */
         erract_c ( "GET", STRLEN, errcon );
         printf   ( "Default error state: %s\n", errcon );
 
 
         /*
         Now start an input loop so we can try different
         settings for error response.
         */
         do
            {
 
            /* Again use ERRACT to retrieve the current error mode. */
            erract_c ( "GET", STRLEN, errcon );
            printf   ( "Current error state: %s\n", errcon );
 
 
            /*
            Okay, input one of the response settings strings
            then set the error subsystem response to that value.
            */
            prompt_c ( "Set error condition (DEFAULT, REPORT, "
                       "ABORT, RETURN, IGNORE) :",
                        STRLEN,
                        errcon );
            erract_c ( "SET", STRLEN, errcon );
 
            /* Cause an error signal. */
            doerr();
 
 
            /*
            Check for an error signal via a call to FAILED.
            At this point we see an important difference
            between the error mode's response to an error
            signal.
            */
            if ( !failed_c() )
               {
               puts( "No error signal noted." );
               }
            else
               {
               puts( "Error signal noted." );
               }
 
            }
         while ( doloop );
 
 
         /*
         Check out of the error subsystem tho' we'll
         never hit this call.
         */
         chkout_c ( "ERRSYSC" );
         exit(0);
         }
 
 
      /* This subroutine initiates a SPICE error signal. */
 
      void doerr ()
         {
 
         /* Check into the error subsystem as before. */
 
         chkin_c ("DOERR");
 
         /*
         Let's signal an error. The string passed by setmsg_c
         is the long error message. You may place markers in the
         long message string then later substitute other data
         items for those markers.
         */
         setmsg_c ( "A truly horrendous event occurred "
                    "during execution of this program. "
                    "Data added to long error message string: "
                    "A double #, an int #, and a string #." );
 
         /*
         Now substitute other data into the long message string.
         Note the substitutions work on the first found marker.
         */
         errdp_c  ( "#", 186282.397 );
         errint_c ( "#", 666        );
         errch_c  ( "#", "A STRING" );
 
 
         /*
         SIGERR causes the error signal with the string passed
         from SETMSG. Set the error flag in the SPICE error
         subsystem and execute the proper error response.
         */
         sigerr_c ( "OOPS(SOMETHINGBAD)" );
 
         chkout_c ( "DOERR" );
 
         }
 
 
 
Run the code example
 
   o- Demo the DEFAULT mode:
 
      Default error state: DEFAULT
      Current error state: DEFAULT
 
   The subsystem is in error state DEFAULT. Let the subsystem run to the
   error signal in DEFAULT mode:
 
      Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE):default
 
   What subsystem reaction occurs in this state?
 
 
      ===================================================================
 
      Toolkit version: N0060
 
      OOPS(SOMETHINGBAD) --
 
      A truly horrendous event occurred during execution of this program.
      Data added to long error message string: A double
      1.8628239700000E+05, an int 666, and a string A STRING.
 
      A traceback follows.  The name of the highest level module is
      first. ERRSYSF --> DOERR
 
      Oh, by the way:  The SPICELIB error handling actions are
      USER-TAILORABLE.  You can choose whether the Toolkit aborts or
      continues when errors occur, which error messages to output, and
      where to send the output.  Please read the ERROR "Required Reading"
      file, or see the routines ERRACT, ERRDEV, and ERRPRT.
 
      ===================================================================
 
 
   Notice we see no error signal status line. The program quit when it
   signaled an error. The program output the error messages, an additional
   information blurb ("Oh by the way"), the Toolkit version, and the
   traceback list.
 
   o- Rerun the program in REPORT mode:
 
       Default error state: DEFAULT
       Current error state: DEFAULT
      Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE) :report
 
      ===================================================================
 
      Toolkit version: N0060
 
      OOPS(SOMETHINGBAD) --
 
      A truly horrendous event occurred during execution of this program.
      Data added to long error message string: A double
      1.8628239700000E+05, an int 666, and a string A STRING.
 
      A traceback follows.  The name of the highest level module is
      first. ERRSYSF --> DOERR
 
      ===================================================================
       Error signal noted.
       Current error state: REPORT
      Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE) :
 
 
 
   The error output ceases after the traceback then returns into the
   calling routine. Note the error signal marker indicates detection of the
   signal. The subsystem in REPORT mode does not print the information
   blurb. The CSPICE system can continue to run after an error signal with
   the error state set to REPORT - this mode flags an error then allows the
   program to continue the run. It may happen that the cause of the error
   condition causes instability in the CSPICE system.
 
   o- Rerun to test ABORT mode:
 
 
      Default error state: DEFAULT
      Current error state: DEFAULT
      Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :abort
 
 
   How does the subsystem respond in ABORT mode?
 
 
 
      ===================================================================
 
      Toolkit version: N0060
 
      OOPS(SOMETHINGBAD) --
 
      A truly horrendous event occurred during execution of this program.
      Data added to long error message string: A double
      1.8628239700000E+05, an int 666, and a string A STRING.
 
      A traceback follows. The name of the highest level module is first.
      ERRSYSF --> DOERR
 
      ===================================================================
 
 
 
   ABORT responds quite like DEFAULT except the error output does not
   include the information blurb shown in the DEFAULT output. All execution
   stops when the error signals.
 
   o- Run the program to demo the RETURN mode:
 
 
      Default error state: DEFAULT
      Current error state: DEFAULT
      Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :return
 
 
   RETURN mode provides the highest measure of flexibility to deal with
   error signals. On output:
 
 
 
      ===================================================================
 
      Toolkit version: N0060
 
      OOPS(SOMETHINGBAD) --
 
      A truly horrendous event occurred during execution of this program.
      Data added to long error message string: A double
      1.8628239700000E+05, an int 666, and a string A STRING.
 
      A traceback follows. The name of the highest level module is first.
      ERRSYSF --> DOERR
 
      ===================================================================
       Error signal noted.
       Current error state: RETURN
 
 
 
   The subroutine signals an error then returns similar to REPORT mode.
   However, this mode includes another property. If we make another pass
   through the command loop:
 
 
      Set error condition (DEFAULT, REPORT, ABORT, RETURN, IGNORE):return
      Error signal noted.
      Current error state: RETURN
 
 
   We see no error output. The main property of the RETURN mode is to allow
   program execution to continue but immediately return from all CSPICE
   routines that check the state of the return_c function. This mode
   restricts program flow after an error signal.
 
   o- And the final mode to test, IGNORE:
 
 
      Default error state: DEFAULT
      Current error state: DEFAULT
      Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :ignore
      No error signal noted.
      Current error state: IGNORE
      Set error condition (DEFAULT,REPORT,ABORT,RETURN,IGNORE) :
 
 
   No error output, no error signal. IGNORE mode prevents expression of all
   error subsystem functions; the subsystem does not set RETURN or FAILED.
   While using IGNORE mode the user cannot identify an error signal.
   Carefully consider program requirements before any use of IGNORE mode.
 
 
Programming Task
--------------------------------------------------------
 
   Write an interactive program to return a state vector based on a user's
   input. Code the program with the capability to recover from user input
   mistakes, inform the user of the mistake, then continue to run.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      /*
      Define the maximum length for any string, 80
      characters plus one null terminator.
      */
      #define STRLEN 81
 
 
      int main( int argc, char **argv )
         {
 
 
         /*  Declare the needed variables: */
 
         SpiceChar              targ [STRLEN];
 
         /*
         Set a flag to start/stop and continue the
         inquiry loop.
         */
         SpiceBoolean           doloop = SPICETRUE;
 
         SpiceDouble            state[6];
         SpiceDouble            ltime;
 
 
         /*
         The RETURN mode signals an error then returns to the
         caller. Just what we need. REPORT mode performs almost
         the same function as RETURN, however RETURN mode
         sets the return_c() value to TRUE and so the program does
         not execute those CSPICE routines that check the return_c()
         value. Consider REPORT mode useful for debugging.
         */
         erract_c ( "SET", STRLEN, "RETURN" );
 
         /*
         Load the data we need for state evaluation.
         */
         furnsh_c ( "meta.tm" );
 
 
         /*
         Start our input query loop to the user.
         */
 
         while ( doloop )
            {
 
            /*
            For simplicity, we request only one input.
            The program calculates the state vector from
            Earth to the user specified target (TARG) in the
            J2000 frame, at ephemeris time zero, using
            aberration correction LT+S (light time plus
            stellar aberration).
            */
            prompt_c ( "Target: ", STRLEN, targ );
 
            if (  eqstr_c( targ, "NONE" ) )
               {
 
               /*
               An exit condition. If the user inputs NONE
               for a target name, set the loop to stop...
               */
               doloop = SPICEFALSE;
 
               }
            else
               {
 
               /*
               ...otherwise evaluate the state between the Earth
               and the target.
               */
               spkezr_c ( targ, 0., "J2000", "LT+S", "EARTH", state,
                          &ltime );
 
               /*
               What if the program can't perform the evaluation?
               Since we set the error subsystem to REPORT we know
               a failed spkezr_c call sets the failed_c flag to
               SPICETRUE then returns control to the calling routine.
               The CSPICE system also outputs an error message
               informing the user of the problem's cause.
 
               Examine the state of failed_c() to determine if we
               output a state vector or not.
               */
 
               if ( ! failed_c() )
                  {
                  printf ( "R : %17.5f %17.5f %17.5f\n",
                           state[0] , state[1], state[2] );
                  printf ( "V : %17.5f %17.5f %17.5f\n",
                           state[3] , state[4], state[5] );
                  printf ( "LT: %f\n", ltime );
                  }
               else
                  {
 
                  /*
                  Problem. Something went wrong. Reset the error
                  subsystem for another pass.
                  */
                  reset_c();
 
                  }
 
               }
 
            }
 
         exit(0);
         }
 
 
 
Run the code example
 
   Now run the code with various inputs to observe behavior. Begin the run
   using known astronomical bodies. Recall the CSPICE default units are
   kilometers, kilometers per second, kilograms, and seconds. The 'R'
   marker identifies the (X,Y,Z) position of the body in kilometers, the
   'V' marker identifies the velocity of the body in kilometers per second,
   and the 'LT' marker identifies the one-way light time between the bodies
   at the requested evaluation time.
 
 
      Target: Moon
      R :     -291584.61659     -266693.40236      -76095.64756
      V :           0.64353          -0.66608          -0.30132
      LT: 1.342311
 
      Target: Mars
      R :   234536077.41914  -132584383.59557   -63102685.70619
      V :          30.95976          28.93646          13.11449
      LT: 923.001080
 
      Target: Pluto barycenter
      R : -1451304742.83853 -4318174144.40632  -918251433.58736
      V :          35.03838           3.06560          -0.01514
      LT: 15501.258293
 
      Target: Puck
 
      ===================================================================
 
      Toolkit version: N0060
 
      SPICE(SPKINSUFFDATA) --
 
      Insufficient ephemeris data has been loaded to compute the state
      of 715 (PUCK) relative to 0 (SOLAR SYSTEM BARYCENTER) at the
      ephemeris epoch 2000 JAN 01 12:00:00.000.
 
      A traceback follows.  The name of the highest level module is
      first.
      spkezr_c --> SPKEZR --> SPKEZ --> SPKAPP --> SPKSSB --> SPKGEO
 
      ===================================================================
 
 
   Perplexing. What happened?
 
   The kernel files named in meta.tm did not include ephemeris data for
   Puck. When the SPK subsystem tried to evaluate Puck's position, the
   evaluation failed due to lack of data, so an error signaled.
 
   The above error signifies an absence of state information at ephemeris
   time 2000 JAN 01 12:00:00.000 (the requested time, ephemeris time zero).
   Since the program set the error mode to RETURN, program execution
   continues.
 
   Try another look-up.
 
 
      Target: Casper
 
      ===================================================================
      Toolkit version: N0060
 
      SPICE(IDCODENOTFOUND) --
 
      The target, 'Casper', is not a recognized name for an ephemeris
      object. The cause of this problem may be that you need an updated
      version of the SPICE Toolkit. Alternatively you may call SPKEZ
      directly if you know the SPICE ID codes for both 'Casper' and
      'EARTH'
 
      A traceback follows.  The name of the highest level module is
      first.
      spkezr_c --> SPKEZR
 
      ===================================================================
 
 
   An easy to understand error. The SPICE system does not contain
   information on a body named 'Casper.'
 
   Another look-up, this time, something easy.
 
 
      Target: Venus
      R :   -80970027.54053  -139655772.57390   -53860125.95820
      V :          31.16969         -27.00018         -12.31622
      LT: 567.655074
 
 
   The look-up succeeded despite two errors in our run. The CSPICE system
   can respond to error conditions (not system errors) in much the same
   fashion as languages with catch/throw instructions.
 
 
Lesson 6: Windows, and Cells
===========================================================================
 
   Lesson Goal:
 
   This lesson introduces the concepts of the SPICE data types 'cell' and
   'window'. A 'cell' is a data structure designed to provide easy and safe
   manipulation of typed array data.
 
   A C SPICE cell consists of a C structure.
 
   A user should create cells by use of the appropriate CSPICE calls. NAIF
   recommends against manual creation of cells.
 
   A 'window' is a type of cell containing ordered, double precision values
   describing a collection of zero or more intervals.
 
   We define an interval, 'i', as all double precision values bounded by
   and including an ordered pair of numbers,
 
         [ a , b ]
            i   i
 
   where
 
         a    <   b
          i   -    i
 
   The intervals within a window are both ordered and disjoint. That is,
   the beginning of each interval is greater than the end of the previous
   interval:
 
         b  <  a
          i     i+1
 
   A common use of the windows facility is to calculate the intersection
   set of a number of time intervals.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   wncomd_c determines the compliment of a window with respect to
            a defined interval.
 
       --   wncond_c contracts a window's intervals.
 
       --   wndifd_c : Calculate the difference between two windows; i.e.
            every point existing in the first but not the second.
 
       --   wnelmd_c returns TRUE or FALSE if a value exists in a window.
 
       --   wnexpd_c expands the size of the intervals in a window.
 
       --   wnextd_c extracts a window's endpoints .
 
       --   wnfetd_c retrieves a specified interval from a window.
 
       --   wnfild_c fills gaps between intervals in a window.
 
       --   wnfltd_c filter/removes small intervals from a window.
 
       --   wnincd_c determines if an interval exists within a window.
 
       --   wninsd_c inserts an interval into a window.
 
       --   wnintd_c calculates the intersection of two windows.
 
       --   wnreld_c compares two windows. Comparison operations available,
            equality '=', inequality '<>', subset '<=' and '>=', proper
            subset '<' and '>'.
 
       --   wnsumd_c creates a window summary.
 
       --   wnunid_c calculates the union of two windows.
 
       --   wnvald_c validates/creates a window from a cell array.
 
 
Requirements and References
--------------------------------------------------------
 
   Knowledge of cells.req, and windows.req documents, as well as the
   other_functions.ppt tutorial file.
 
 
Programming task:
--------------------------------------------------------
 
   Given the times of line-of-sight for a vehicle from a ground station and
   the times for an acceptable Sun-station-vehicle phase angle, write a
   program to determine the time intervals common to both configurations.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdio.h>
      #include "SpiceUsr.h"
      #include <stdlib.h>
      #include <string.h>
 
      #define MAXSIZ       8
 
      /*
      Define the maximum length for a UTC string, 25
      characters plus one null terminator.
      */
      #define UTCLEN       26
 
      int main( int argc, char **argv )
         {
 
         /*
         Define our variable types.
 
         Define the cells to use as windows.
         The windows can hold 8 data values i.e.
         four intervals.
         */
 
         SPICEDOUBLE_CELL ( loswin, MAXSIZ );
         SPICEDOUBLE_CELL ( phswin, MAXSIZ );
         SPICEDOUBLE_CELL ( sched , MAXSIZ );
 
         SpiceInt         i;
         SpiceInt         small;
         SpiceInt         large;
 
         SpiceChar        utcstr[2][UTCLEN];
 
         /*
         Define sets of time intervals. For the purposes of this
         tutorial program, define time intervals representing
         an unobscured line of sight between a ground station
         and some  body.
         */
         SpiceChar   los   [MAXSIZ][UTCLEN] =
                       { "Jan 1, 2003 22:15:02", "Jan 2, 2003  4:43:29",
                         "Jan 4, 2003  9:55:30", "Jan 4, 2003 11:26:52",
                         "Jan 5, 2003 11:09:17", "Jan 5, 2003 13:00:41",
                         "Jan 6, 2003 00:08:13", "Jan 6, 2003  2:18:01"
                       };
 
         /*
         A second set of intervals representing the times for which
         an acceptable phase angle exits between the ground station,
         the body and the Sun.
         */
         SpiceChar   phase [MAXSIZ][UTCLEN] =
                       { "Jan 2, 2003 00:03:30", "Jan 2, 2003 19:00:00",
                         "Jan 3, 2003  8:00:00", "Jan 3, 2003  9:50:00",
                         "Jan 5, 2003 12:00:00", "Jan 5, 2003 12:45:00",
                         "Jan 6, 2003 00:30:00", "Jan 6, 2003 23:00:00"
                       };
 
         SpiceDouble      left;
         SpiceDouble      right;
         SpiceDouble      meas;
         SpiceDouble      avg;
         SpiceDouble      stddev;
         SpiceDouble      los_et [MAXSIZ];
         SpiceDouble      phs_et [MAXSIZ];
 
 
         /* Load our meta kernel for the leapseconds data. */
         furnsh_c ( "meta.tm" );
 
 
         /*
         Windows consist of double precision values, convert the
         time tags defined in the LOS and PHASE arrays to
         double precision ET. Store the double values in the
         loswin and phswin arrays.
         */
         for ( i=0; i < MAXSIZ; ++i )
            {
            str2et_c ( los[i]  , &los_et[i] );
            str2et_c ( phase[i], &phs_et[i] );
            }
 
         /*
         Initialize the cells from the double precision arrays,
         then validate the cells as windows.
 
         Since we use 4 intervals, set the window to accept 8 (MAXSIZ)
         data values ( 4 * 2 = 8 ). Since we require no more than
         8 data values, assign a window size of 8.
         */
 
         memmove ( (SpiceDouble*)loswin.data,
                   los_et,
                   MAXSIZ * sizeof(SpiceDouble) );
 
         memmove ( (SpiceDouble*)phswin.data,
                   phs_et,
                   MAXSIZ * sizeof(SpiceDouble) );
 
         wnvald_c ( MAXSIZ, MAXSIZ, &loswin );
         wnvald_c ( MAXSIZ, MAXSIZ, &phswin );
         wnvald_c ( MAXSIZ, MAXSIZ, &sched  );
 
 
         /*
         The issue for consideration, at what times do line of
         sight events coincide with acceptable phase angles?
         Perform the set operation AND on loswin, phswin,
         place the results in the window 'sched'.
         */
 
         wnintd_c ( &loswin, &phswin, &sched );
 
         puts   ( " " );
         printf ( "No. data values in sched            : %d\n",
                                                  (int)card_c(&sched) );
         printf ( "Space available for values in sched : %d\n",
                                                  (int)size_c(&sched) );
 
         /*
         Output the results. The number of intervals in 'sched'
         is half the number of data points (the cardinality).
         Use a call to card_c to retrieve the window's cardinality.
         */
         puts ( " " );
         puts ( "Time intervals meeting defined criterion.");
 
         for ( i=0; i < card_c(&sched)/2 ; ++i )
            {
 
            /*
            Extract from the derived 'sched' the values defining the
            time intervals, [small, large].
            */
            wnfetd_c ( &sched, i, &left, &right );
 
            /*
            Convert the ET values to UTC for human comprehension.
            */
            et2utc_c ( left , "C", 3, UTCLEN, utcstr[0] );
            et2utc_c ( right, "C", 3, UTCLEN, utcstr[1] );
 
            /*
            Output the UTC string and the corresponding index
            for the interval.
            */
            printf ( " %d  %s %s\n", (int)i, utcstr[0], utcstr[1] );
 
            }
 
         puts ( " " );
         puts ( "Summary of sched window" );
 
         wnsumd_c ( &sched, &meas, &avg, &stddev, &small, &large );
 
         /*
         Summarize the 'sched' window.
         */
         printf( "o Total measure of sched    : %12.5f\n", meas   );
         printf( "o Average measure of sched  : %12.5f\n", avg    );
         printf( "o Standard deviation of\n "                     );
         printf(  " the measures in sched     : %12.5f\n", stddev );
 
 
         /*
         The values for small and large refer to the indexes of the
         values in the window ('sched'). The shortest interval is
 
               [ SPICE_CELL_ELEM_D( &sched, small),
                 SPICE_CELL_ELEM_D( &sched, small+1) ];
 
         the longest is
 
               [ SPICE_CELL_ELEM_D( &sched, large),
                 SPICE_CELL_ELEM_D( &sched, large+1) ];
 
         Output the indexes for the shortest and longest
         intervals. As C bases an array index on 0, the interval
         index is half the array index.
         */
         printf ( "o Index of shortest interval: %d\n", (int)small/2 );
         printf ( "o Index of longest interval : %d\n", (int)large/2 );
 
         exit (0);
         }
 
 
 
Run the code example
 
   The output window has the name SCHED (schedule).
 
   Output the amount of data held in SCHED compared to the maximum possible
   amount.
 
       No. data values in SCHED            :   6
       Space available for values in SCHED :   8
 
   List the time intervals for which a line of sight exists during the time
   of a proper phase angle.
 
 
      Time intervals meeting defined criterion.
       0  2003 JAN 02 00:03:30.000 2003 JAN 02 04:43:29.000
       1  2003 JAN 05 12:00:00.000 2003 JAN 05 12:45:00.000
       2  2003 JAN 06 00:30:00.000 2003 JAN 06 02:18:01.000
 
 
   Finally, an analysis of the SCHED data. The measure of an interval [a,b]
   (a <= b) equals b-a. Real values output in units of seconds.
 
 
      Summary of sched window
      o Total measure of sched    :  25980.00001
      o Average measure of sched  :   8660.00000
      o Standard deviation of
        the measures in sched     :   5958.55022
      o Index of shortest interval: 1
      o Index of longest interval : 0
 
 
 
Lesson 7: Utility and Constants Routines
===========================================================================
 
   Lesson Goals:
 
   CSPICE provides several routines to perform commonly needed tasks. Among
   these:
 
       --   convert values between unit expressions
 
       --   determine the equality of strings
 
       --   indicate whether a file exists
 
       --   identify the toolkit version
 
   CSPICE also includes a set of functions that return constant values
   often used in astrodynamics, time calculations, and geometry.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   convrt_c converts between measurements units
 
       --   tkvrsn_c returns the current version of the toolkit
 
       --   eqstr_c returns a boolean describing the equality of two
            strings. The comparison is case insensitive and ignores spaces.
 
       --   exists_c returns a boolean indicating the existence of a file.
 
       --   clight_c : velocity of light in a vacuum, kilometers per second
 
       --   dpr_c : number of degrees per radian (180/Pi)
 
       --   rpd_c : number radians per degree (Pi/180)
 
       --   spd_c : number of seconds per day (60*60*24)
 
       --   b1900_c : Julian Date of the epoch Besselian Date 1900.0
 
       --   b1950_c : Julian date of the epoch Besselian Date 1950.0
 
       --   j1900_c : Julian date of 1900 JAN 0.5 this corresponds to
            calendar date 1899 DEC 31 12:00:00
 
       --   j1950_c : Julian date of 1950 JAN 1.0 this corresponds to
            calendar date 1950 JAN 01 00:00:00
 
       --   j2000_c : Julian date of 2000 JAN 1.5 (2000 JAN 01 12:00:00)
 
       --   j2100_c : Julian date of 2100 JAN 1.5, this corresponds to
            calendar date 2100 JAN 01 12:00:00
 
       --   twopi_c : double precision value of 2 * Pi
 
       --   pi_c : double precision value of Pi
 
       --   halfpi_c : double precision value of 0.5 * Pi
 
       --   jyear_c : seconds per Julian year (365.25 Julian days)
 
       --   tyear_c : seconds per tropical year (approximately the number
            of seconds from one spring equinox to the next)
 
 
Requirements and References
--------------------------------------------------------
 
   The references used to define or calculate the constants functions are
   found in the source code file and/or the API reference. Also reference
   the other_functions.ppt tutorial file.
 
 
Programming Task
--------------------------------------------------------
 
   Write an interactive program to convert values between various units.
   Demonstrate the flexibility of the unit conversion routine, the string
   equality function, and show the version ID function.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdio.h>
      #include <stdlib.h>
      #include <string.h>
      #include "SpiceUsr.h"
 
      #define UTCLEN       32
 
      void tostan ( SpiceChar * alias );
 
      int main( int argc, char **argv )
         {
 
         /*
         Define the few variables needed for data input
         and output.
         */
 
         SpiceChar           funits [UTCLEN];
         SpiceChar           tunits [UTCLEN];
         SpiceChar           fromstr[UTCLEN];
         SpiceDouble         fvalue;
         SpiceDouble         tvalue;
 
         /*
         Define the tkvrsn_c return value.
         */
         ConstSpiceChar     * vers;
 
         /*
         Display the Toolkit version string with a
         tkvrsn_c call.
         */
         vers = tkvrsn_c( "TOOLKIT" );
         printf( "\n Convert demo program compiled against "
                    "CSPICE Toolkit %s\n\n", vers );
 
         /*
         The user first inputs the name of a unit of measure.
         Send the name through TOSTAN for de-aliasing.
         */
         prompt_c ( "From Units : ", UTCLEN, funits );
         tostan   ( funits );
 
         /*
         Input a double precision value to express in a new
         unit format.
         */
         prompt_c ( "From Value : ", UTCLEN, fromstr );
         prsdp_c ( fromstr, &fvalue );
 
         /*
         Now the user inputs the name of the output units.
         Again we send the units name through TOSTAN for
         de-aliasing.
         */
         prompt_c ( "To Units   : ", UTCLEN, tunits );
         tostan ( tunits );
 
         convrt_c ( fvalue, funits, tunits, &tvalue );
         printf ( "%f %s\n", tvalue, tunits );
 
         exit(0);
         }
 
 
      void tostan ( SpiceChar * alias )
         {
 
         /*
         As a convenience, let's alias a few common terms
         to their appropriate counterpart. Use eqstr_c
         to compare strings. The comparison ignores
         letter case and trailing/leading spaces.
         */
 
         if ( eqstr_c ( alias, "meter" ) )
            {
 
            /*
            First, a 'meter' by any other name is a
            'METER' and smells as sweet ...
            */
            strcpy ( alias, "METERS");
 
            }
         else if ( eqstr_c ( alias, "klicks"     ) ||
                   eqstr_c ( alias, "kilometers" ) ||
                   eqstr_c ( alias, "kilometer"  )   )
            {
 
            /*
            ... 'klicks' and 'KILOMETERS' and
            'KILOMETER' identifies 'KM'....
            */
            strcpy ( alias, "KM");
 
            }
         else if ( eqstr_c ( alias, "secs") )
            {
 
            /*
            ... 'secs' to 'SECONDS'.
            */
            strcpy ( alias, "SECONDS");
 
            }
         else if ( eqstr_c ( alias, "miles") )
            {
 
            /*
            ... and finally 'miles' to 'STATUTE_MILES'.
            Normal people think in statute miles.
            Only sailors think in nautical miles - one
            minute of arc at the equator.
            */
            strcpy ( alias, "STATUTE_MILES");
 
            }
 
         /*
         Much better. Now return. If the input matched
         none of the aliases, this routine did nothing.
         */
 
         }
 
 
 
Run the code example
 
   Run a few conversions through the application to ensure it works. The
   intro banner gives us the Toolkit version against which the application
   was linked:
 
 
       Convert demo program compiled against CSPICE Toolkit CSPICE_N0060
 
      From Units : klicks
      From Value : 3
      To Units   : miles
      1.864114 STATUTE_MILES
 
 
   Now we know. Three kilometers equals 1.864 miles.
 
   Legend states Pheidippides ran from the Marathon Plain to Athens. The
   modern marathon race (inspired by this event) spans 26.2 miles. How far
   in kilometers?
 
 
       Convert demo program compiled against CSPICE Toolkit CSPICE_N0060
 
      From Units : miles
      From Value : 26.2
      To Units   : km
      42.164813 km
 
 
 
Programming Task
--------------------------------------------------------
 
   Write a program to output CSPICE constants and use those constants to
   calculate some rudimentary values.
 
 
Code Solution
--------------------------------------------------------
 
 
      #include <stdlib.h>
      #include <stdio.h>
      #include <strings.h>
      #include "SpiceUsr.h"
 
      int main( int argc, char **argv )
         {
 
         /*
         All the functions have the same calling sequence:
 
            VALUE = function_name();
            some_procedure( function_name() );
            printf ( "%19.12f\n", function_name() );
 
         First a simple example using the seconds per day
         constant...
         */
         printf ("Number of (S)econds (P)er (D)ay           : %19.12f\n",
                                                          spd_c() );
 
         /*
         ...then show the value of degrees per radian, 180/Pi...
         */
         printf ("Number of (D)egrees (P)er (R)adian        : %19.16f\n",
                                                          dpr_c() );
 
         /*
         ...and the inverse, radians per degree, Pi/180.
         It is obvious dpr_c() equals 1.0/rpd_c(), or more simply
         dpr_c() * rpd_c() equals 1.0.
         */
         printf("Number of (R)adians (P)er (D)egree        : %19.16f\n",
                                                          rpd_c() );
 
         /*
         What's the value for the astrophysicist's favorite
         physical constant (in a vacuum)?
         */
         printf ("Speed of light in KM per second           : %19.12f\n",
                                                        clight_c() );
 
         /*
         How long (in Julian days) from the J2000 epoch to the
         J2100 epoch?
         */
         printf ("Number of days between epochs J2000  \n"        );
         printf ("  and J2100                               : %19.12f\n",
                                            j2100_c() - j2000_c()  );
 
         /*
         Redo the calculation returning seconds...
         */
         printf ("Number of seconds between epochs\n"             );
         printf ("  J2000 and J2100                         : %19.5f\n",
                                spd_c() * (j2100_c() - j2000_c() ) );
 
         /*
         ...then tropical years.
         */
         printf ( "Number of tropical years between\n"             );
         printf ( "  epochs J2000 and J2100                 : %19.12f\n",
                ( spd_c() / tyear_c() ) * (j2100_c() - j2000_c() ) );
 
         /*
         Finally, how can I convert a radian value to degrees.
         */
         printf ("Number of degrees in Pi/2 radians of arc  : %19.16f\n",
                                              halfpi_c() * dpr_c() );
 
         /*
         and degrees to radians.
         */
         printf ("Number of radians in 250 degrees of arc   : %19.16f\n",
                                                       250. * rpd_c() );
 
         exit(0);
         }
 
 
 
Run the code example
 
 
      Number of (S)econds (P)er (D)ay           :  86400.000000000000
      Number of (D)egrees (P)er (R)adian        : 57.2957795130823229
      Number of (R)adians (P)er (D)egree        :  0.0174532925199433
      Speed of light in KM per second           : 299792.457999999984
      Number of days between epochs J2000
        and J2100                               :  36525.000000000000
      Number of seconds between epochs
        J2000 and J2100                         :    3155760000.00000
      Number of tropical years between
        epochs J2000 and J2100                  :    100.002135902909
      Number of degrees in Pi/2 radians of arc  : 90.0000000000000000
      Number of radians in 250 degrees of arc   :  4.3633231299858242
 
 
