Preface - Other Stuff (The Red Shirt topics) (C)





March 28, 2005

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 a several 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 includes several lessons to demonstrate use of the less celebrated CSPICE routines.



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, or IDL, 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 Reading and Users Guides



NAIF Required Reading (*.req) documents introduce the functionality of particular CSPICE subsystems:

 
      cells.req       ek.req          intrdctn.req    problems.req
      ck.req          ellipses.req    kernel.req      rotation.req
      cspice.req      error.req       naif_ids.req    scanning.req
      daf.req         frames.req      pck.req         sclk.req
      das.req         icy.req         planes.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        convert.ug      spacit.ug       tictoc.ug
      chronos.ug      inspekt.ug      spkmerge.ug     tobin.ug
      ckbrief.ug      mkspk.ug        states.ug       toxfr.ug
      commnt.ug       simple.ug       subpt.ug        version.ug
 
These text documents exist in the 'doc' directory of the main Toolkit directory:

      ../cspice/doc/
HTML format documentation

As of delivery N57, the CSPICE distributions include HTML versions of Required Readings and Users Guides, accessible from the HTML documentation directory:

      ../cspice/doc/html/index.html


Source Code



All SPICELIB and CSPICE source files include usage and design information incorporated in a comment block known as the "header."

A header consists of several marked sections:

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.

      ..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:

 
      \begintext
 
         ... commentary information on the data assignments ...
 
      \begindata
 
         ... data assignments ...
 


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 lessons may include kernels a program must load to operate. For this workbook, a user can download all kernels from the NAIF anonymous ftp site:

      ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels
 
      FILE NAME                TYPE  DESCRIPTION
      -----------------------  ----  ----------------------
      naif0007.tls             LSK   Generic LSK
      leapseconds.tls          LSK   The current leapseconds
                                     kernel (naif0007.tls as
                                     of May 2004)
      de405s.bsp               SPK   Planet Ephemeris SPK
      pck00007.tpc             PCK   Generic PCK


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 us of the kernel subsystem to load, unload, and list loaded kernels. Comprehension of kernel file data access precedence. Data loaded last (later) has precedence over similar data loaded first (earlier).

This lesson requires creation of a SPICE meta kernel.



Relevant Routines






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.ker) in this lesson. Either a kernel with explicit path information:

 
   \begindata
 
      KERNELS_TO_LOAD = ( 'kernels/spk/de405s.bsp',
                          'kernels/pck/pck00007.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 = ( '$LSK/naif0007.tls',
                          '$SPK/de405s.bsp',
                          '$PCK/pck00007.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.ker";
 
 
      /*
      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.ker
   Type   META
   Source
 
   File   kernels/spk/de405s.bsp
   Type   SPK
   Source meta.ker
 
   File   kernels/pck/pck00007.tpc
   Type   TEXT
   Source meta.ker
 
   File   kernels/lsk/naif0007.tls
   Type   TEXT
   Source meta.ker
 
   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.ker) 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/pck00007.tpc',
                          '$LSK/leapseconds.tls')
 
   \begintext


Relevant Routines






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.ker" );
 
      /*
      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 ( eqstr_c( "N", &type ) )
            {
 
            /*
            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 ( eqstr_c( "C", &type ) )
            {
 
            /*
            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:     122170.00000000
      Numeric value:     136780.00000000
      Numeric value:     1.0000000000000D-01
      Numeric value:     1.0000000000000D-01
      Numeric value:    0.50000000000000
 
    BODY699_RING2
     No. items:   5   Of type: N
      Numeric value:     117580.00000000
      Numeric value:     122170.00000000
      Numeric value:   0.
      Numeric value:   0.
      Numeric value:   0.
 
    BODY699_RING1_1_NAME
     No. items:   1   Of type: C
      String value: Encke Gap
 
    BODY699_RING2_NAME
     No. items:   1   Of type: C
      String value: Cassini Division
 
    BODY699_RING1_NAME
     No. items:   1   Of type: C
      String value: A Ring
 
    BODY699_RING1_1
     No. items:   5   Of type: N
      Numeric value:     133405.00000000
      Numeric value:     133730.00000000
      Numeric value:   0.
      Numeric value:   0.
      Numeric value:   0.
 
Note the final time value differs from the previous values in the final two 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:          134094896.78900
     Time value:          134094896.78900
     Time value:          134094896.78975
 


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






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.ker" );
 
 
      /*
      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, <ime);
 
 
      /*
      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, <ime);
 
      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  : 70.973950
       Lat  : -4.989675
 
Spherical.

 
      Spherical
       Rad  : 369340.815193
       Lon  : 70.973950
       Colat: 94.989675
 
Geodetic. The cartographic lat/lon.

 
      Geodetic
       Rad  : 362962.836755
       Lon  : 70.973950
       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






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 81
 
   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/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);
 
      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:






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: N0057
 
   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
How does the REPORT reaction differ from DEFAULT? A demo to illustrate...

 
 
   ===================================================================
 
   Toolkit version: N0057
 
   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: N0057
 
   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: N0057
 
   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.ker" );
 
 
      /*
      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,
                       <ime );
 
            /*
            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: N0057
 
   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 --> S
 
   ===================================================================
 
Perplexing. What happened?

The kernel files named in meta.ker 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: N0057
 
   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, Sets, and Cells





Lesson Goal:

This lesson introduces the concepts of the CSPICE data types 'cell' and 'window. A 'cell' is as the basis for set calculations in CSPICE. A 'window' permits a user to manipulate continuous intervals of the real line. A 'window' is nothing more than an ordered, double precision cell that contains zero or more intervals

An interval being an ordered pair of numbers,

      [ a(i), b(i) ]
where

      a(i)  <  b(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(i)  <  a(i+1)
A common use of a window is to calculate when the time intervals covering known events, eclipses, occultation, right ascension within a certain value, etc intersect.



Relevant Routines






Requirements and References




Knowledge of cells.req, sets.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.ker" );
 
 
      /*
      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 include calls to convert values between unit expressions, determine the equality of strings, and indicate whether a file exists.

CSPICE also includes a set of functions that return constant values often used in astrodynamics, time calculations, and geometry.



Relevant Routines






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, "clicks"     ) ||
                eqstr_c ( alias, "kilometers" ) ||
                eqstr_c ( alias, "kilometer"  )   )
         {
 
         /*
         ... 'clicks' 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_N0057
   >From Units : clicks
   >From Value : 3
   To Units   : miles
        1.8641135767120 STATUTE_MILES
 
Now we know. Three kilometers equals 1.864 miles.

Pheidippides ran 26.2 miles from the Marathon Plain to Athens. How far in kilometers?

 
   >From Units : miles
   >From Value : 26.2
   To Units   : km
        42.164812800000 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