 
Preface - Other Stuff (The Red Shirt topics) (FORTRAN)
===========================================================================
 
   October 20, 2008
 
   The extensive scope of the SPICE 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
   SPICE 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 SPICE 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 SPICE 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 SPICE 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 SPICE
   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:
 
         ../toolkit/doc/
 
   HTML format documentation
 
   The SPICE distributions include HTML versions of Required Readings and
   Users Guides, accessible from the HTML documentation directory:
 
         ../toolkit/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 SPICE 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 SPICE system.
 
   The source code for SPICE products is stored in 'src' sub-directory of
   the main SPICE directory:
 
         ../toolkit/src/
 
   Find the SPICELIB library source code in:
 
         ../toolkit/src/spicelib/
 
 
API Documentation
 
   The SPICELIB package includes the SPICELIB Reference Guide, an index of
   all SPICELIB 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.
 
         ...spicelib/doc/html/spicelib/index.html
 
 
Tutorials
 
   A set of Microsoft PowerPoint presentations provide a general overview
   of the complete SPICE 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 loads the meta kernel and the SPICE kernels listed
            within that kernel.
 
       --   KTOTAL retrieves the number of SPICE kernels loaded by the
            kernel subsystem.
 
       --   KDATA returns information about each loaded kernel.
 
       --   UNLOAD removes a kernel and deletes any pool variables defined
            by that kernel from the kernel subsystem.
 
       --   KCLEAR 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 SPICE 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:
 
 
            PROGRAM KERNEL
            IMPLICIT NONE
 
      C
      C     Declare the needed variables:
      C
            CHARACTER*(32) META
            CHARACTER*(32) FILE
            CHARACTER*(32) TYPE
            CHARACTER*(32) SOURCE
 
            INTEGER        COUNT
            INTEGER        I
            INTEGER        HANDLE
 
            LOGICAL        FOUND
 
      C
      C     Assign the path name of the meta kernel to META.
      C
            META = 'meta.tm'
 
      C
      C     Load the meta kernel then use KTOTAL to interrogate the
      C     SPICE kernel subsystem for the total number of loaded kernel
      C     files. KTOTAL accepts as input values:
      C
      C                   SPK  --- all SPK files are counted in the total.
      C                   CK   --- all CK files are counted in the total.
      C                   PCK  --- all binary PCK files are counted in
      C                            the total.
      C                   EK   --- all EK files are counted in the total.
      C                   TEXT --- all text kernels that are not
      C                            meta-text kernels are included in the
      C                            total.
      C                   META --- all meta-text kernels are counted in
      C                            the total.
      C                   ALL  --- every type of kernel is counted in the
      C                            total.
      C
      C     We want the count of all kernels, so use 'ALL'.
      C
            CALL FURNSH ( META )
            CALL KTOTAL ( 'ALL', COUNT )
 
            WRITE(*,*) 'Kernel count after load: ', COUNT
 
      C
      C     Loop over the number of files; interrogate the SPICE system
      C     with KDATA for the kernel names, kernel source,
      C     and the type. 'FOUND' returns a boolean indicating whether
      C     any kernel files of the specified type were loaded by
      C     the kernel subsystem. This example ignores checking 'FOUND'
      C     as kernels are known to be loaded.
      C
            DO I=1, COUNT
 
               CALL KDATA ( I, 'ALL', FILE, TYPE, SOURCE, HANDLE,
           .                FOUND )
 
               WRITE(*,*) 'File   ', FILE
               WRITE(*,*) 'Type   ', TYPE
               WRITE(*,*) 'Source ', SOURCE
               WRITE(*,*) ' '
 
            END DO
 
      C
      C     Unload one kernel then check the count.
      C
            CALL UNLOAD ( 'kernels/spk/de405s.bsp' )
            CALL KTOTAL ( 'ALL', COUNT )
 
      C
      C     The subsystem should report one less kernel.
      C
            WRITE(*,*) 'Kernel count after one unload: ', COUNT
 
      C
      C     Now unload the meta kernel. This action unloads all
      C     files listed in the meta kernel.
      C
            CALL UNLOAD ( META )
 
      C
      C     Check the count. SPICE should return a count of zero.
      C
            CALL KTOTAL ( 'ALL', COUNT )
            WRITE(*,*) 'Kernel count after meta unload: ', COUNT
 
            END
 
 
 
Run the code example
 
   First we see the number of all loaded kernels returned from the KTOTAL
   call:
 
 
       Kernel count after load:   4
 
 
   Now the KDATA 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 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 SPICE 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 retrieves integer values from the kernel subsystem.
 
       --   GDPOOL retrieves double precision values from the kernel
            subsystem
 
       --   GCPOOL retrieves character values from the kernel subsystem
 
       --   DTPOOL returns data (name, type, size) describing a kernel pool
            variable.
 
       --   GNPOOL 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 file
   pool.f, most pool routines exist in pool.f as entry points, or the 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
--------------------------------------------------------
 
 
            PROGRAM KERVAR
            IMPLICIT NONE
 
      C
      C     Note, the pool routines return a boolean to 'FOUND'
      C     signaling whether the requested variable name exists
      C     in the kernel pool. The code solutions do not check the
      C     boolean value since the solutions use variables known to
      C     exist. In general, code should always check the boolean
      C     value to ensure return of valid data.
      C
 
      C
      C     Define the max number of kernel variables
      C     of concern for this examples.
      C
            INTEGER                     N_ITEMS
            PARAMETER                  (N_ITEMS = 20 )
 
      C
      C     Define the maximum length for any string.
      C
            INTEGER                     STRLEN
            PARAMETER                  (STRLEN = 80 )
 
      C
      C     As usual, type our variables...
      C
            INTEGER                     I
            INTEGER                     J
            INTEGER                     DIM
            INTEGER                     N_VAR
            INTEGER                     N_VAL
            INTEGER                     START
 
            LOGICAL                     FOUND
 
            DOUBLE PRECISION            DVARS    (N_ITEMS)
 
            CHARACTER* (STRLEN)         CVALS    (N_ITEMS)
            CHARACTER* (STRLEN)         CVARS    (N_ITEMS)
            CHARACTER* (12)             TYPE
            CHARACTER* (12)             TMPLATE
 
      C
      C     ...and two SPICELIB routines we use.
      C
            INTEGER                     LASTNB
            LOGICAL                     EQSTR
 
      C
      C     Load the example kernel containing the kernel variables.
      C     The kernels defined in KERNELS_TO_LOAD load into the
      C     kernel pool with this call.
      C
            CALL FURNSH ('cassini.tm' )
 
      C
      C     Initialize the START value. This values indicates
      C     index of the first element to return if a kernel
      C     variable is an array. START = 1 mean return everything.
      C     START = 2 indicates return everything but the first element.
      C
            START = 1
 
      C
      C     Set the template for the variable names to find. Let's
      C     look for all variables containing  the string RING.
      C     Define this with the wildcard template '*RING*'. Note:
      C     the template '*RING' would match any variable name
      C     ending with the RING string.
      C
            TMPLATE =  '*RING*'
 
      C
      C     We're ready to interrogate the kernel pool for
      C     the variables matching the template. GNPOOL tells us:
      C
      C        1. Does the kernel pool contain any variables that
      C           match the template (value of FOUND).
      C        2. If so, how many variables? (value of N_VAL)
      C        3. The variable names. (CVALS, an array of strings)
      C
            CALL GNPOOL ( TMPLATE, START, STRLEN, N_VAL, CVALS, FOUND )
 
            IF ( FOUND ) THEN
               WRITE(*,*) 'No. variables matching template: ', N_VAL
               WRITE(*,*)
            ELSE
                WRITE(*,*) 'No kernel variables matched template'
                STOP
            ENDIF
 
      C
      C     Okay, now we know something about the kernel pool
      C     variables of interest to us. Let's find out more...
      C
            DO I=1, N_VAL
 
      C
      C        Use DTPOOL to return the dimension and TYPE,
      C        C (character) or N (numeric), of each pool
      C        variable name in the CVALS array.
      C
      C        The SPICE function LASTNB returns the index of
      C        the last non-blank character in the CVALS string.
      C        This is convenient to trim the trailing whitespace
      C        of a string.
      C
               CALL DTPOOL ( CVALS(I), FOUND, DIM, TYPE )
               WRITE(*,*) CVALS(I)(1:LASTNB(CVALS(I)) )
               WRITE(*,*) ' No. items: ', DIM, '   Of type: ', TYPE
 
      C
      C        Use the EQSTR routine to test character equality,
      C        'N' (numeric) or 'C' (character).
      C
               IF ( EQSTR( 'N', TYPE ) ) THEN
 
      C
      C           If TYPE equals 'N', we found a numeric array.
      C           In this case any numeric array will be an array
      C           of double precision numbers ("doubles"). GDPOOL
      C           retrieves doubles from the kernel pool. DVARS
      C           contains the array of N_VAR values.
      C
                  CALL GDPOOL ( CVALS(I), START, N_ITEMS,
           .                                     N_VAR  , DVARS, FOUND )
                  DO J=1 ,N_VAR
                     WRITE(*,*) '  Numeric value: ', DVARS(J)
                  END DO
 
               ELSE IF ( EQSTR( 'C', TYPE ) ) THEN
 
      C
      C           If TYPE equals 'C', we found a string array.
      C           GCPOOL retrieves string values from the
      C           kernel pool. CVARS contains the array of N_VAR
      C           values.
      C
                  CALL GCPOOL ( CVALS(I), START, N_ITEMS,
           .                                     N_VAR, CVARS, FOUND )
                  DO J=1 ,N_VAR
                     WRITE(*,*) '  String value: ',
           .                    CVARS(J)(1:LASTNB(CVARS(J)) )
                  END DO
 
               END IF
 
               WRITE(*,*)
 
            END DO
 
      C
      C     Now look at the time variable EXAMPLE_TIMES. Extract this
      C     value as an array of doubles.
      C
            CALL GDPOOL ( 'EXAMPLE_TIMES', START, N_ITEMS,
           .                               N_VAR  , DVARS, FOUND )
 
            WRITE(*,*) 'EXAMPLE_TIMES'
 
            DO J=1 ,N_VAR
               WRITE(*,*) '  Time value (ET): ', DVARS(J)
            END DO
 
            END
 
 
 
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 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 loop, a second loop outputs the
   contents of the data variable using GCPOOL or GDPOOL.
 
 
       BODY699_RING1
        No. items:   5    Of type: N
         Numeric value:   122170.000000000
         Numeric value:   136780.000000000
         Numeric value:   0.100000000000000
         Numeric value:   0.100000000000000
         Numeric value:   0.500000000000000
 
       BODY699_RING2
        No. items:   5    Of type: N
         Numeric value:   117580.000000000
         Numeric value:   122170.000000000
         Numeric value:   0.000000000000000
         Numeric value:   0.000000000000000
         Numeric value:   0.000000000000000
 
       BODY699_RING1_1
        No. items:   5    Of type: N
         Numeric value:   133405.000000000
         Numeric value:   133730.000000000
         Numeric value:   0.000000000000000
         Numeric value:   0.000000000000000
         Numeric value:   0.000000000000000
 
       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 (ET):   134094896.789000
         Time value (ET):   134094896.789000
         Time value (ET):   134094896.789753
 
 
 
Lesson 3: Coordinate Conversions
===========================================================================
 
   Lesson Goals:
 
   The SPICE 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, latitudinal to rectangular
 
       --   LATCYL, latitudinal to cylindrical
 
       --   LATSPH, latitudinal to spherical
 
       --   RECCYL, rectangular to cylindrical
 
       --   RECGEO, rectangular to geodetic
 
       --   RECLAT, rectangular to latitudinal
 
       --   RECSPH, rectangular to spherical
 
       --   RECRAD, rectangular to right ascension - declination
 
       --   SPHREC, spherical to rectangular
 
       --   SPHCYL, spherical to cylindrical
 
       --   SPHLAT, spherical to latitudinal
 
       --   CYLLAT, cylindrical to latitudinal
 
       --   CYLSPH, cylindrical to spherical
 
       --   CYLREC, cylindrical to rectangular
 
       --   GEOREC, 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
--------------------------------------------------------
 
 
            PROGRAM COORD
            IMPLICIT NONE
 
      C
      C     Type the variables.
      C
            INTEGER              DIM
 
            CHARACTER*(32)       INRFRM
            CHARACTER*(32)       NONFRM
            CHARACTER*(32)       TIMSTR
 
            DOUBLE PRECISION     ET
            DOUBLE PRECISION     RANGE
            DOUBLE PRECISION     RA
            DOUBLE PRECISION     DEC
            DOUBLE PRECISION     LAT
            DOUBLE PRECISION     COLAT
            DOUBLE PRECISION     LON
            DOUBLE PRECISION     LTIME
            DOUBLE PRECISION     FLAT
            DOUBLE PRECISION     RAD   (3)
            DOUBLE PRECISION     POS   (3)
 
      C
      C    Declare the SPICELIB function to scale radians to degrees.
      C
            DOUBLE PRECISION     DPR
 
            INRFRM = 'J2000'
            NONFRM = 'IAU_EARTH'
 
      C
      C     Load the needed kernels using a FURNSH call on a
      C     meta kernel.
      C
            CALL FURNSH ( 'meta.tm' )
 
      C
      C     Prompt the user for a time string. Convert the
      C     time string to ephemeris time J2000 (ET).
      C
            CALL PROMPT ( 'Time of interest: ', TIMSTR )
            CALL STR2ET ( TIMSTR, ET )
 
      C
      C     Access the kernel pool data for the triaxial radii of the
      C     Earth. 'RAD(1)' holds the equatorial radius, 'RAD(2)'
      C     the polar radius.
      C
            CALL BODVRD ( 'EARTH', 'RADII', 3, DIM, RAD)
 
      C
      C     Calculate the flattening factor for the Earth.
      C
      C              equatorial_radius - polar_radius
      C     flat =   ________________________________
      C
      C                    equatorial_radius
      C
            FLAT = (RAD(1) - RAD(3))/RAD(1)
 
      C
      C     Make the SPKPOS call to determine the apparent position
      C     of the Moon w.r.t. to the Earth at ET in the inertial frame.
      C
            CALL SPKPOS ( 'MOON', ET, INRFRM, 'LT+S','EARTH',
           .               POS  , LTIME)
 
      C
      C     Show the current frame and time.
      C
            WRITE(*,*) 'Time : ', TIMSTR
            WRITE(*,*) ' Inertial Frame: ', INRFRM
 
 
      C
      C     First, convert the position vector
      C     X = POS(1), Y = POS(2), Z = POS(3), to RA/DEC.
      C
            CALL RECRAD ( POS, RANGE, RA, DEC )
            WRITE(*,*) '  Range/Ra/Dec'
            WRITE(*,*) '   Range: ', RANGE
            WRITE(*,*) '   RA   : ', RA * DPR()
            WRITE(*,*) '   DEC  : ', DEC* DPR()
 
      C
      C     ...latitudinal coordinates...
      C
            CALL RECLAT ( POS, RANGE, LON, LAT )
            WRITE(*,*) '  Latitudinal'
            WRITE(*,*) '   Rad  : ', RANGE
            WRITE(*,*) '   Lon  : ', LON * DPR()
            WRITE(*,*) '   Lat  : ', LAT * DPR()
 
      C
      C     ...spherical coordinates use the colatitude,
      C     the angle from the Z axis.
      C
            CALL RECSPH ( POS, RANGE, COLAT, LON )
            WRITE(*,*) '  Spherical'
            WRITE(*,*) '   Rad  : ', RANGE
            WRITE(*,*) '   Lon  : ', LON   * DPR()
            WRITE(*,*) '   Colat: ', COLAT * DPR()
 
      C
      C     Make the SPKPOS call to determine the apparent position
      C     of the Moon w.r.t. to the Earth at ET in the non-inertial,
      C     body fixed, frame.
      C
            CALL SPKPOS ( 'MOON', ET, NONFRM, 'LT+S','EARTH',
           .               POS, LTIME)
 
            WRITE(*,*)
            WRITE(*,*) ' Non-inertial Frame: ', NONFRM
 
      C
      C     ...latitudinal coordinates...
      C
            CALL RECLAT ( POS, RANGE, LON, LAT )
            WRITE(*,*) '  Latitudinal'
            WRITE(*,*) '   Rad  : ', RANGE
            WRITE(*,*) '   Lon  : ', LON * DPR()
            WRITE(*,*) '   Lat  : ', LAT * DPR()
 
      C
      C     ...spherical coordinates...
      C
            CALL RECSPH ( POS, RANGE, COLAT, LON )
            WRITE(*,*) '  Spherical'
            WRITE(*,*) '   Rad  : ', RANGE
            WRITE(*,*) '   Lon  : ', LON   * DPR()
            WRITE(*,*) '   Colat: ', COLAT * DPR()
 
      C
      C     ...finally, convert the position to geodetic
      C     coordinates.
      C
            CALL RECGEO ( POS, RAD(1), FLAT, LON, LAT, RANGE )
            WRITE(*,*) '  Geodetic'
            WRITE(*,*) '   Rad  : ', RANGE
            WRITE(*,*) '   Lon  : ', LON * DPR()
            WRITE(*,*) '   Lat  : ', LAT * DPR()
 
            WRITE(*,*)
 
            END
 
 
 
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:   369340.815193344
          RA   :   203.643685679514
          DEC  :  -4.97901037468640
 
 
   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  :   369340.815193344
          Lon  :  -156.356314320486
          Lat  :  -4.97901037468640
 
 
   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  :   369340.815193344
          Lon  :  -156.356314320486
          Colat:   94.9790103746864
 
 
   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  :   369340.815193344
          Lon  :   70.9869500300845
          Lat  :  -4.98967514376289
 
 
   Spherical.
 
 
         Spherical
          Rad  :   369340.815193344
          Lon  :   70.9869500300845
          Colat:   94.9896751437629
 
 
   Geodetic. The cartographic lat/lon.
 
 
         Geodetic
          Rad  :   362962.836755033
          Lon  :   70.9869500300845
          Lat  :  -4.99024928580030
 
 
 
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 SPICE.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   STR2ET converts time strings to ephemeris time (ET).
 
       --   TIMOUT formats a time string output.
 
       --   TPICTR creates a format template for use in TIMOUT.
 
       --   TSETYR 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 for a list of the string markers used
   by TIMOUT and TPICTR to describe time string format. Always keep in mind
   STR2ET 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 SPICE-supported formats.
 
 
Code Solution
--------------------------------------------------------
 
   Caution: Be sure to assign sufficient string lengths for time
   formats/pictures.
 
 
            PROGRAM TIC
            IMPLICIT NONE
 
      C
      C     Declare the needed variables:
      C
            CHARACTER*(256)      ERROR
            CHARACTER*(50)      PICTR1
            CHARACTER*(50)      PICTR2
            CHARACTER*(50)      PICTR3
            CHARACTER*(50)      TIMSTR
            CHARACTER*(32)      LSK
 
            DOUBLE PRECISION    ET
            DOUBLE PRECISION    ET1
            DOUBLE PRECISION    ET2
            DOUBLE PRECISION    JYEAR
 
            LOGICAL             OK
 
      C
      C     Assign the LSK variable to the name of the leapsecond,
      C     kernel and create an arbitrary time string.
      C
            LSK    = '/kernels/gen/lsk/leapseconds.tls'
            TIMSTR = 'Mar 15, 2003 12:34:56.789 AM PST'
 
      C
      C     Load the leapseconds kernel.
      C
            CALL FURNSH ( LSK )
 
            WRITE(*,*) 'Original time string       : ', TIMSTR
 
      C
      C     Convert the time string to the number of ephemeris
      C     seconds past the J2000 epoch. This is the most common
      C     internal time representation used by the SPICE
      C     system; SPICE refers to this as ephemeris time (ET).
      C
            CALL STR2ET ( TIMSTR, ET )
            WRITE(*,*) 'Corresponding ET           : ', ET
 
      C
      C     Make a picture of an output format. Describe a Unix-like
      C     time string then send the picture and the ET value through
      C     TIMOUT to format and convert the ET representation of
      C     the time string into the form described by PICTR1. The
      C     '::UTC-7' token indicates the time zone for the TIMSTR
      C     output - PDT. 'PDT' is part of the output, but not a time
      C     system token.
      C
            PICTR1 = 'Wkd Mon DD HR:MN:SC PDT YYYY ::UTC-7'
            CALL TIMOUT ( ET, PICTR1, TIMSTR )
            WRITE(*,*) 'Time in string format 1    : ', TIMSTR
 
      C
      C     Create another picture. This time combine a calendar,
      C     2 digit year, with a Julian Day format.
      C
            PICTR2 = 'Wkd Mon DD HR:MN ::UTC-7 YR (JULIAND.##### JDUTC)'
            CALL TIMOUT ( ET, PICTR2, TIMSTR )
            WRITE(*,*) 'Time in string format 2    : ', TIMSTR
 
      C
      C     Why create a picture by hand when SPICE can do it for you?
      C     Input a string to TPICTR with the format of interest.
      C     'OK' returns a boolean indicating whether an error
      C     occurred while parsing the picture string, if so,
      C     an error diagnostic message returns in 'ERROR'. In this
      C     example, no need exists to check the error flag since
      C     the picture string is known as correct.
      C
            CALL TPICTR ( '12:34:56.789 P.M. PDT January 1, 2006',
           .              PICTR3, OK, ERROR )
 
 
      C
      C     Confirm the TPICTR call succeeded. Report the error string
      C     if not.
      C
            IF( .NOT. OK ) THEN
               WRITE(*,*)
               WRITE(*,*) 'Error in TPICTR call: '
               WRITE(*,*)  ERROR
               STOP
            END IF
 
 
            CALL TIMOUT ( ET, PICTR3, TIMSTR )
            WRITE(*,*) 'Time in string format 3    : ', TIMSTR
 
      C
      C     Two digit year representations often cause problems due to
      C     the ambiguity of the century. The routine TSETYR gives the
      C     user the ability to set a default range for 2 digit year
      C     representation. SPICE uses 1969AD as the default start
      C     year so the numbers inclusive of 69 to 99 represent
      C     years 1969AD to 1999AD, the numbers inclusive of 00 to 68
      C     represent years 2000AD to 2068AD.
      C
      C     Define a time string with  a two-digit year. Since
      C     the SPICE base year is 1969, the time subsystem interprets
      C     the string as 1979.
      C
            TIMSTR = 'Mar 15, 79 12:34:56'
            CALL STR2ET ( TIMSTR, ET1 )
 
      C
      C     Setting 1980 as the base year causes SPICE to interpret the
      C     year values 80 to 99 as 1980AD to 1999AD; the year values
      C     00 to 79 as 2000AD to 2079AD.
      C
            CALL TSETYR ( 1980 )
            CALL STR2ET ( TIMSTR, ET2 )
 
      C
      C     Calculate the number of years between the two ET
      C     representations, ~100.
      C
            WRITE(*,*) 'Years between evaluations: ',(ET2 - ET1)/JYEAR()
 
            END
 
 
 
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 :   100.000000475321
 
 
 
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 returns TRUE if a SPICE error signaled.
 
       --   RESET resets the error subsystem to the state prior to an error
            signal - WARNING, this call resets only the error subsystem,
            the rest of the SPICE system is unchanged.
 
       --   ERRACT sets the reaction of the error subsystem to an error.
 
       --   ERRCH inserts a character/string into an error message.
 
       --   ERRDP inserts a double precision value into an error message.
 
       --   ERRINT inserts an integer value into an error message.
 
       --   ERRDEV sets the device for error output.
 
       --   ERRPRT sets the error message items for output on an error
            signal.
 
       --   SIGERR signals a SPICE error with a given short message.
 
       --   SETMSG sets the long message corresponding to SIGERR.
 
       --   RETURN 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
--------------------------------------------------------
 
 
            PROGRAM ERRSYS
            IMPLICIT NONE
 
      C
      C     Define needed variables.
      C
            CHARACTER*(32)    ERRCON
 
            LOGICAL           DOLOOP
            LOGICAL           FAILED
 
            DOLOOP         = .TRUE.
 
      C
      C     Check into the error subsystem to create a traceback
      C     showing the call tree. A CHKOUT must balance every
      C     CHKIN.
      C
            CALL CHKIN( 'ERRSYSF' )
 
      C
      C     Before we start, what's the initial (default)
      C     error state? ERRACT both sets the state and
      C     reports the state.
      C
            CALL ERRACT ( 'GET', ERRCON )
            WRITE(*,*) 'Default error state: ', ERRCON
 
 
      C
      C     Now start an input loop so we can try different
      C     settings for error modes.
      C
            DO WHILE ( DOLOOP )
 
      C
      C        Again use ERRACT to retrieve the current error mode.
      C
               CALL ERRACT ( 'GET', ERRCON )
               WRITE(*,*) 'Current error state: ', ERRCON
 
      C
      C        Okay, input one of the response settings strings
      C        then set the error subsystem mode to that value.
      C
               CALL PROMPT ( 'Set error condition (DEFAULT, REPORT, '
           .              // 'ABORT, RETURN, IGNORE) :', ERRCON )
               CALL ERRACT ( 'SET', ERRCON )
 
      C
      C        Cause an error signal.
      C
               CALL DOERR
 
      C
      C        Check for an error signal via a call to FAILED.
      C        At this point we see an important difference
      C        between the error mode's responses to an error
      C        signal.
      C
               IF ( .NOT. FAILED() ) THEN
 
                  WRITE(*,*) 'No error signal noted.'
 
               ELSE
 
                  WRITE(*,*) 'Error signal noted.'
 
               END IF
 
            END DO
 
      C
      C     Check out of the error subsystem tho' we'll
      C     never hit this call.
      C
            CALL CHKOUT ( 'ERRSYSF' )
 
            STOP
            END
 
 
 
      C
      C     This subroutine initiates a SPICE error signal.
      C
            SUBROUTINE DOERR
 
      C
      C     Check into the error subsystem as before.
      C
            CALL CHKIN( 'DOERR' )
 
      C
      C     Let's signal an error. The string passed by SETMSG
      C     is the long error message. You may place markers in the
      C     long message string then later substitute other data
      C     items for those markers.
      C
            CALL SETMSG ( 'A truly horrendous event occurred '
           .          //  'during execution of this program. '
           .          //  'Data added to long error message string: '
           .          //  'A double #, an int #, and a string #.' )
 
      C
      C     Now substitute other data into the long message string.
      C     Note the substitutions work on the first found marker.
      C
            CALL ERRDP ( '#', 186282.397D0 )
            CALL ERRINT( '#', 666          )
            CALL ERRCH ( '#', 'A STRING'   )
 
      C
      C     SIGERR causes the error signal with the string passed
      C     from SETMSG. Set the error flag in the SPICE error
      C     subsystem and execute the proper error response.
      C
            CALL SIGERR ( 'OOPS(SOMETHINGBAD)' )
 
            CALL CHKOUT( 'DOERR' )
 
            RETURN
            END
 
 
 
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 SPICE 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 SPICE 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 SPICE
   routines that check the state of the RETURN 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
--------------------------------------------------------
 
 
            PROGRAM ADERR
            IMPLICIT NONE
 
      C
      C     Declare our variables.
      C
            CHARACTER*( 32 )    TARG
 
            LOGICAL             DOLOOP
            LOGICAL             EQSTR
            LOGICAL             FAILED
 
            DOUBLE PRECISION    STATE(6)
            DOUBLE PRECISION    LTIME
 
 
      C
      C     First important action. The DEFAULT error setting
      C     in the SPICE system displays an error message when
      C     an error signals then quits the program. We want the
      C     error message, but no 'quit.'
      C
      C     The RETURN mode signals an error then returns to the
      C     caller. Just what we need. REPORT mode performs almost
      C     the same function as RETURN, however RETURN mode
      C     sets the RETURN() value to TRUE and so the program does
      C     not execute those SPICE routines that check the RETURN()
      C     value. Consider REPORT mode useful for debugging.
      C
            CALL ERRACT( 'SET', 'RETURN'  )
 
      C
      C     Load the data we need for state evaluation.
      C
            CALL FURNSH( 'meta.tm' )
 
      C
      C     Set a flag to start/stop and continue the
      C     inquiry loop.
      C
            DOLOOP     = .TRUE.
 
      C
      C     Start our input query loop to the user.
      C
            DO WHILE ( DOLOOP )
 
      C
      C        For simplicity, we request only one input.
      C        The program calculates the state vector from
      C        Earth to the user specified target (TARG) in the
      C        J2000 frame, at ephemeris time zero, using
      C        aberration correction LT+S (light time plus
      C        stellar aberration).
      C
               CALL PROMPT ( 'Target: ', TARG )
 
               IF (  EQSTR( TARG, 'NONE' ) ) THEN
 
      C
      C           An exit condition. If the user inputs NONE
      C           for a target name, set the loop to stop...
      C
                  DOLOOP = .FALSE.
 
               ELSE
 
      C
      C           ...otherwise evaluate the state between the Earth
      C           and the target.
      C
                  CALL SPKEZR ( TARG, 0.D0, 'J2000', 'LT+S', 'EARTH',
           .                    STATE, LTIME )
 
      C
      C           What if the program can't perform the evaluation?
      C           Since we set the error subsystem to RETURN we know
      C           a failed SPKEZR call sets the FAILED flag to
      C           TRUE then returns control to the calling routine.
      C           The SPICE system also outputs an error message
      C           informing the user of the problem's cause.
      C
      C           Examine the state of FAILED() to determine if we
      C           output a state vector or not.
      C
                  IF ( .NOT. FAILED() ) THEN
                     WRITE(*,*) 'R : ', STATE(1), STATE(2), STATE(3)
                     WRITE(*,*) 'V : ', STATE(4), STATE(5), STATE(6)
                     WRITE(*,*) 'LT: ', LTIME
 
                  ELSE
 
      C
      C              Problem. The FAILED() routine returned a TRUE.
      C              Reset the error subsystem for another pass.
      C
                     CALL RESET()
 
                  END IF
 
               END IF
 
            END DO
 
            END
 
 
 
Run the code example
 
   Now run the code with various inputs to observe behavior. Begin the run
   using known astronomical bodies. Recall the SPICE 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 :  -291584.616594972 -266693.402359092 -76095.6475582799
       V :   0.643527473361488 -0.666082437142091 -0.301323100073823
       LT:   1.34231060609343
 
      Target: Mars
       R :   234536077.419136 -132584383.595569 -63102685.7061911
       V :   30.9597590600082  28.9364646866516  13.1144901558867
       LT:   923.001080471163
 
      Target: Pluto barycenter
       R :  -1451304742.83853 -4318174144.40632 -918251433.587357
       V :   35.0383792683026  3.06559507376708 -1.513976282647267E-002
       LT:   15501.2582930189
 
      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 --> 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
 
      ===================================================================
 
 
   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 :  -80970027.5405320 -139655772.573898 -53860125.9582014
       V :   31.1696929135543 -27.0001825841033 -12.3162192672805
       LT:   567.655074271531
 
 
   The look-up succeeded despite two errors in our run. The SPICE 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 FORTRAN SPICE cell consists of a structured 1xN array.
 
   A user should create cells by use of the appropriate SPICE 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 determines the compliment of a window with respect to a
            defined interval.
 
       --   WNCOND contracts a window's intervals.
 
       --   WNDIFD : Calculate the difference between two windows; i.e.
            every point existing in the first but not the second.
 
       --   WNELMD returns TRUE or FALSE if a value exists in a window.
 
       --   WNEXPD expands the size of the intervals in a window.
 
       --   WNEXTD extracts a window's endpoints .
 
       --   WNFETD retrieves a specified interval from a window.
 
       --   WNFILD fills gaps between intervals in a window.
 
       --   WNFLTD filter/removes small intervals from a window.
 
       --   WNINCD determines if an interval exists within a window.
 
       --   WNINSD inserts an interval into a window.
 
       --   WNINTD calculates the intersection of two windows.
 
       --   WNRELD compares two windows. Comparison operations available,
            equality '=', inequality '<>', subset '<=' and '>=', proper
            subset '<' and '>'.
 
       --   WNSUMD creates a window summary.
 
       --   WNUNID calculates the union of two windows.
 
       --   WNVALD 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
--------------------------------------------------------
 
 
            PROGRAM WIN
            IMPLICIT NONE
 
      C
      C     Define our variable types.
      C
            INTEGER           LBCELL
            PARAMETER        (LBCELL = -5 )
 
            INTEGER           MAXSIZ
            PARAMETER        (MAXSIZ = 8 )
 
            INTEGER           I
            INTEGER           SMALL
            INTEGER           LARGE
 
 
            CHARACTER * 32    LOS   ( MAXSIZ )
            CHARACTER * 32    PHASE ( MAXSIZ )
            CHARACTER * 26    UTCSTR( 2 )
 
      C
      C     Define the cells to use as windows.
      C     The windows can hold 8 data values i.e.
      C     four intervals.
      C
            DOUBLE PRECISION  LOSWIN(LBCELL:MAXSIZ)
            DOUBLE PRECISION  PHSWIN(LBCELL:MAXSIZ)
            DOUBLE PRECISION  SCHED (LBCELL:MAXSIZ)
 
            DOUBLE PRECISION  LEFT
            DOUBLE PRECISION  RIGHT
            DOUBLE PRECISION  MEAS
            DOUBLE PRECISION  AVG
            DOUBLE PRECISION  STDDEV
 
      C
      C     SPICELIB functions associated with windows.
      C
            INTEGER           CARDD
            INTEGER           SIZED
 
      C
      C    Define sets of time intervals. For the purposes of this
      C    tutorial program, define time intervals representing
      C    an unobscured line of sight between a ground station
      C    and some  body.
      C
            DATA     LOS / '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'
           .             /
 
      C
      C    A second set of intervals representing the times for which
      C    an acceptable phase angle exits between the ground station,
      C    the body and the Sun.
      C
            DATA   PHASE / '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'
           .             /
 
 
      C
      C     Load our meta kernel for the leapseconds data.
      C
            CALL FURNSH ( 'meta.tm' )
 
      C
      C     Windows consist of double precision values, convert the
      C     time tags defined in the LOS and PHASE arrays to
      C     double precision ET. Store the double values in the
      C     LOSWIN and PHSWIN arrays. Null out SCHED before attempting
      C     to validate - this removes any garbage values.
      C
            DO I = 1, 8
               CALL STR2ET( LOS(I)  , LOSWIN(I) )
               CALL STR2ET( PHASE(I), PHSWIN(I) )
               SCHED(I) = 0.d0
            END DO
 
 
      C
      C     Validate the windows from the double precision cells.
      C     Since we use 4 intervals, the set the window to accept 8
      C     data values ( 4 * 2 = 8 ). Since we require no more than
      C     8 data values, assign a window size of 8.
      C
            CALL WNVALD ( 8, 8, LOSWIN )
            CALL WNVALD ( 8, 8, PHSWIN )
            CALL WNVALD ( 8, 8, SCHED  )
 
      C
      C     The issue for consideration, at what times do line of
      C     sight events coincide with acceptable phase angles?
      C     Perform the set operation AND on LOSWIN, PHSWIN,
      C     place the results in the window SCHED.
      C
            CALL WNINTD( LOSWIN, PHSWIN, SCHED )
 
            CALL TOSTDO ( ' ' )
            WRITE(*,*) 'No. data values in SCHED            : ',
           .                                                CARDD(SCHED)
            WRITE(*,*) 'Space available for values in SCHED : ',
           .                                                SIZED(SCHED)
 
      C
      C     Output the results. The number of intervals in SCHED
      C     is half the number of data points (the cardinality).
      C     Use a call to CARDD to retrieve the window's cardinality.
      C
            CALL TOSTDO ( ' ' )
            CALL TOSTDO ( 'Time intervals meeting defined criterion.')
 
            DO I = 1, CARDD( SCHED )/2
 
      C
      C        Extract from the derived SCHED the values defining the
      C        time intervals, [LEFT, RIGHT].
      C
               CALL WNFETD ( SCHED, I, LEFT, RIGHT )
 
      C
      C        Convert the ET values to UTC for human comprehension.
      C
               CALL ET2UTC ( LEFT , 'C', 3, UTCSTR(1) )
               CALL ET2UTC ( RIGHT, 'C', 3, UTCSTR(2) )
 
      C
      C        Output the UTC string and the corresponding index
      C        for the interval.
      C
               WRITE(*,*)  I, '  ', UTCSTR(1), ' ',UTCSTR(2)
 
            END DO
 
      C
      C     Summarize the SCHED window.
      C
            CALL TOSTDO ( ' ' )
            CALL TOSTDO ( 'Summary of SCHED window' )
            CALL WNSUMD ( SCHED, MEAS, AVG, STDDEV, SMALL, LARGE )
 
            WRITE(*,*) 'o Total measure of SCHED    : ', MEAS
            WRITE(*,*) 'o Average measure of SCHED  : ', AVG
            WRITE(*,*) 'o Standard deviation of '
            WRITE(*,*) '  the measures in SCHED     : ', STDDEV
 
      C
      C     The values for SMALL and LARGE refer to the indexes of the
      C     values in the array (SCHED). The shortest interval
      C     is [ SCHED(SMALL), SCHED(SMALL+1)]; the longest is
      C     [ SCHED(LARGE), SCHED(LARGE+1)]. Output the indexes for
      C     the shortest and longest intervals.
      C
      C
            WRITE(*,*) 'o Index of shortest interval: ', (SMALL+1)/2
            WRITE(*,*) 'o Index of longest interval : ', (LARGE+1)/2
 
            END
 
 
 
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.
         1   2003 JAN 02 00:03:30.000   2003 JAN 02 04:43:29.000
         2   2003 JAN 05 12:00:00.000   2003 JAN 05 12:45:00.000
         3   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    :   25980.0000087023
       o Average measure of SCHED  :   8660.00000290076
       o Standard deviation of
         the measures in SCHED     :   5958.55021716516
       o Index of shortest interval:   2
       o Index of longest interval :   1
 
 
 
Lesson 7: Utility and Constants Routines
===========================================================================
 
   Lesson Goals:
 
   SPICE 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
 
   SPICE also includes a set of functions that return constant values often
   used in astrodynamics, time calculations, and geometry.
 
 
Relevant Routines
--------------------------------------------------------
 
       --   CONVRT converts between measurements units
 
       --   TKVRSN returns the current version of the toolkit
 
       --   EQSTR returns a boolean describing the equality of two strings.
            The comparison is case insensitive and ignores spaces.
 
       --   EXISTS returns a boolean indicating the existence of a file.
 
       --   CLIGHT : velocity of light in a vacuum, kilometers per second
 
       --   DPR : number of degrees per radian (180/Pi)
 
       --   RPD : number radians per degree (Pi/180)
 
       --   SPD : number of seconds per day (60*60*24)
 
       --   B1900 : Julian Date of the epoch Besselian Date 1900.0
 
       --   B1950 : Julian date of the epoch Besselian Date 1950.0
 
       --   J1900 : Julian date of 1900 JAN 0.5 this corresponds to
            calendar date 1899 DEC 31 12:00:00
 
       --   J1950 : Julian date of 1950 JAN 1.0 this corresponds to
            calendar date 1950 JAN 01 00:00:00
 
       --   J2000 : Julian date of 2000 JAN 1.5 (2000 JAN 01 12:00:00)
 
       --   J2100 : Julian date of 2100 JAN 1.5, this corresponds to
            calendar date 2100 JAN 01 12:00:00
 
       --   TWOPI : double precision value of 2 * Pi
 
       --   PI : double precision value of Pi
 
       --   HALFPI : double precision value of 0.5 * Pi
 
       --   JYEAR : seconds per Julian year (365.25 Julian days)
 
       --   TYEAR : 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
--------------------------------------------------------
 
 
            PROGRAM UNITS
            IMPLICIT NONE
 
      C
      C     Define the few variables
      C     needed for data input and output.
      C
            CHARACTER* (32)   FUNITS
            CHARACTER* (32)   TUNITS
 
            DOUBLE PRECISION  FVALUE
            DOUBLE PRECISION  TVALUE
 
      C
      C     Define the TKVRSN return value.
      C
            CHARACTER*(12)    VERS
 
      C
      C     Display the Toolkit version string with a
      C     TKVRSN call.
      C
            CALL TKVRSN( 'TOOLKIT', VERS )
            WRITE(*,*)
            WRITE(*,*) 'Convert demo program compiled against '
           .       //  'SPICE Toolkit ', VERS
            WRITE(*,*)
 
      C
      C     The user first inputs the name of a unit of measure.
      C     Send the name through TOSTAN for de-aliasing.
      C
            CALL PROMPT ( 'From Units : ', FUNITS )
            CALL TOSTAN ( FUNITS )
 
      C
      C     Input a double precision value to express in a new
      C     unit format.
      C
            WRITE(*,'(A13$)') 'From Value : '
            READ (*,*)         FVALUE
 
      C
      C     Now the user inputs the name of the output units.
      C     Again we send the units name through TOSTAN for
      C     de-aliasing.
      C
            CALL PROMPT ( 'To Units   : ', TUNITS )
            CALL TOSTAN ( TUNITS )
 
      C
      C     Call CONVRT to perform the conversion. CONVRT
      C     signals an error if:
      C        1. Either unit is unknown.
      C        2. The input and output units are not in the same
      C           class (length, angular measure, or time).
      C
            CALL CONVRT ( FVALUE, FUNITS, TUNITS, TVALUE )
 
      C
      C     Output the results.
      C
            WRITE(*,*) TVALUE, ' ' , TUNITS
 
            STOP
            END
 
 
      C
      C     As a convenience, let's alias a few common terms
      C     to their appropriate counterpart. Use EQSTR to
      C     compare strings. The comparison ignores letter
      C     case and trailing/leading spaces.
      C
            SUBROUTINE TOSTAN ( ALIAS )
            IMPLICIT NONE
 
            LOGICAL           EQSTR
            CHARACTER*(*)     ALIAS
 
      C
      C     Start de-aliasing. Check the input string
      C     against a set of defined (allowed) aliases.
      C
            IF ( EQSTR( ALIAS, 'meter' ) ) THEN
 
      C
      C        First, a 'meter' by any other name is a
      C        'METER' and smells as sweet ...
      C
               ALIAS = 'METERS'
 
            ELSE IF ( EQSTR( ALIAS, 'klicks'     )   .OR.
           .          EQSTR( ALIAS, 'KILOMETERS' )   .OR.
           .          EQSTR( ALIAS, 'KILOMETER'  ) ) THEN
 
      C
      C        ... 'klicks', 'KILOMETERS' and
      C        'KILOMETER' identifies 'KM'....
      C
               ALIAS = 'KM'
 
            ELSE IF ( EQSTR( ALIAS, 'secs' ) )THEN
 
      C
      C        ... 'secs' to 'SECONDS'.
      C
               ALIAS = 'SECONDS'
 
            ELSE IF ( EQSTR( ALIAS, 'miles' ) )THEN
 
      C
      C        ... and finally 'miles' to 'STATUTE_MILES'.
      C        Normal people think in statute miles. Only
      C        sailors think in nautical miles - one
      C        minute of arc at the equator.
      C
               ALIAS = 'STATUTE_MILES'
 
            END IF
 
      C
      C     Much better, so return. If the input matched
      C     none of the aliases, this routine did nothing.
      C
            RETURN
            END
 
 
 
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 SPICE Toolkit N0060
 
      From Units : klicks
      From Value : 3
      To Units   : miles
         1.86411357671200  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 SPICE Toolkit N0060
 
      From Units : miles
      From Value : 26.2
      To Units   : km
         42.1648128000000  km
 
 
 
Programming Task
--------------------------------------------------------
 
   Write a program to output SPICE constants and use those constants to
   calculate some rudimentary values.
 
 
Code Solution
--------------------------------------------------------
 
 
            PROGRAM CONST
            IMPLICIT NONE
 
      C
      C     As required in FORTRAN define the (return) type for
      C     the functions. All the functions have the same calling
      C     sequence:
      C
      C        VALUE = function_name()
      C        CALL some_procedure( function_name() )
      C        WRITE(*,*) function_name()
      C
            DOUBLE PRECISION      CLIGHT
            DOUBLE PRECISION      DPR
            DOUBLE PRECISION      RPD
            DOUBLE PRECISION      SPD
            DOUBLE PRECISION      J2000
            DOUBLE PRECISION      HALFPI
            DOUBLE PRECISION      J2100
            DOUBLE PRECISION      TYEAR
 
      C
      C     First a simple example using the seconds per day
      C     constant...
      C
            WRITE(*,*) 'Number of (S)econds (P)er (D)ay         : ',
           .            SPD()
 
      C
      C     ...then show the value of degrees per radian, 180/Pi...
      C
            WRITE(*,*) 'Number of (D)egrees (P)er (R)adian      : ',
           .            DPR()
 
      C
      C     ...and the inverse, radians per degree, Pi/180.
      C     It is obvious DPR() equals 1.D/RPD(), or more simply
      C     DPR() * RPD() equals 1
      C
            WRITE(*,*) 'Number of (R)adians (P)er (D)egree      : ',
           .            RPD()
 
      C
      C     What's the value for the astrophysicist's favorite
      C     physical constant (in a vacuum)?
      C
            WRITE(*,*) 'Speed of light in KM per second         : ',
           .            CLIGHT()
 
      C
      C     How long (in Julian days) from the J2000 epoch to the
      C     J2100 epoch?
      C
            WRITE(*,*) 'Number of days between epochs J2000'
            WRITE(*,*) '  and J2100                             : ',
           .            J2100() - J2000()
 
      C
      C     Redo the calculation returning seconds...
      C
            WRITE(*,*) 'Number of seconds between epochs'
            WRITE(*,*) '  J2000 and J2100                       : ',
           .            SPD() * (J2100() - J2000() )
 
      C
      C     ...then tropical years.
      C
            WRITE(*,*) 'Number of tropical years between'
            WRITE(*,*) '  epochs J2000 and J2100                : ',
           .            ( SPD() / TYEAR() ) * (J2100() - J2000() )
 
      C
      C     Finally, how can I convert a radian value to degrees.
      C
            WRITE(*,*) 'Number of degrees in Pi/2 radians of arc: ',
           .            HALFPI() * DPR()
 
      C
      C     and degrees to radians.
      C
            WRITE(*,*) 'Number of radians in 250 degrees of arc : ',
           .            250.D0 * RPD()
 
            END
 
 
 
Run the code example
 
 
       Number of (S)econds (P)er (D)ay         :   86400.0000000000
       Number of (D)egrees (P)er (R)adian      :   57.2957795130823
       Number of (R)adians (P)er (D)egree      :   1.745329251994330E-002
       Speed of light in KM per second         :   299792.458000000
       Number of days between epochs J2000
         and J2100                             :   36525.0000000000
       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:   90.0000000000000
       Number of radians in 250 degrees of arc :   4.36332312998582
 
 
