 
Preface - Other Stuff (The Red Shirt topics) (IDL)
===========================================================================
 
     March 28, 2005
 
     The extensive scope of the ICY 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 ICY 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, Sets, and Cells
 
         7.   Utility and Constants Routines
 
 
NAIF Documentation
--------------------------------------------------------
 
     The technical complexity of the various ICY 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 ICY System
     or other NAIF product:
 
         --   Required Readings and Users Guides
 
         --   Source Code Documentation
 
         --   API Documentation
 
         --   Tutorials
 
 
Required Reading and Users Guides
 
     NAIF Required Reading (*.req) documents introduce the functionality of
     particular ICY 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 ICY
     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:
 
           ../icy/doc/
 
     HTML format documentation
 
     As of delivery N57, the ICY distributions include HTML versions of
     Required Readings and Users Guides, accessible from the HTML
     documentation directory:
 
          ../icy/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:
 
         --   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 ICY 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 ICY system.
 
     The source code for ICY products is stored in 'src' sub-directory of
     the main ICY directory:
 
 
API Documentation
 
     The Icy 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.
 
           ..icy/doc/html/cspice/index.html
 
     Also included is Icy Reference Guide, an index of all Icy APIs with
     hyperlinks to API specific documentation. Each API documentation page
     includes cross-links to any other Icy APIs mentioned in the document
     and a link to the API documentation for the CSPICE routine called by
     the Icy interface.
 
           ..icy/doc/html/icy/index.html
 
 
Tutorials
 
     A set of Microsoft PowerPoint presentations provide a general overview
     of the complete ICY 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.   A text kernel containing non-native line terminators causes a
              no-op when read by the kernel subsystem, i.e. the state of
              the kernel pool does not change. To reduce the aggravations
              cause by this situation, as of N57 the cspice_furnsh call
              includes a line terminator check, signaling an error on
              non-native text files.
 
 
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
--------------------------------------------------------
 
         --   cspice_furnsh loads the meta kernel and the SPICE kernels
              listed within that kernel.
 
         --   cspice_ktotal retrieves the number of SPICE kernels loaded by
              the kernel subsystem.
 
         --   cspice_kdata returns information about each loaded kernel.
 
         --   cspice_unload removes a kernel 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 ICY 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:
 
 
        PRO KERNEL
 
           ;;
           ;; Assign the path name of the meta kernel to META.
           ;;
           META = 'meta.ker'
 
           ;;
           ;; Load the meta kernel then use KTOTAL to interrogate the SPICE
           ;; kernel subsystem.
           ;;
           cspice_furnsh, META
           cspice_ktotal, 'ALL', count
           print, 'Kernel count after load: ', 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 = 0, (count-1)  do begin
              cspice_kdata, i, 'ALL', file, type, source, handle, found
              print, 'File   ' + file
              print, 'Type   ' + type
              print, 'Source ' + source
              print
           endfor
 
           ;;
           ;; Unload one kernel then check the count.
           ;;
           cspice_unload, 'kernels/spk/de405s.bsp'
           cspice_ktotal, 'ALL', count
 
           ;;
           ;; The subsystem should report one less kernel.
           ;;
           print, 'Kernel count after one unload : ', count
 
           ;;
           ;; Now unload the meta kernel. This action unloads all
           ;; files listed in the meta kernel.
           ;;
           cspice_unload, META
 
           ;;
           ;; Check the count. Icy should return a count of zero.
           ;;
           cspice_ktotal, 'ALL', count
           print, 'Kernel count after meta unload: ', count
 
        END
 
 
 
Run the code example
 
     First we see the number of all loaded kernels returned from the
     cspice_ktotal call:
 
 
         Kernel count after load:   4
 
 
     Now the cspice_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 cspice_furnsh 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 ICY 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
--------------------------------------------------------
 
         --   cspice_gipool retrieves integer values from the kernel
              subsystem.
 
         --   cspice_gdpool retrieves double precision values from the
              kernel subsystem
 
         --   cspice_gcpool retrieves character values from the kernel
              subsystem
 
         --   cspice_dtpool returns data (name, type, size) describing a
              kernel pool variable.
 
         --   cspice_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 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
--------------------------------------------------------
 
 
        PRO KERVAR
 
           ;;
           ;; Define the max number of kernel variables
           ;; of concern for this examples.
           ;;
           N_ITEMS =  20
 
           ;;
           ;; Define the maximum length for any string. 80 characters,
           ;; plus on for the C null terminator.
           ;;
           STRLEN  = 81
 
           ;;
           ;; Load the example kernel containing the kernel variables.
           ;; The kernels defined in KERNELS_TO_LOAD load into the
           ;; kernel pool with this call.
           ;;
           cspice_furnsh, "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.
           ;;
           tmplate = "*RING*"
 
           ;;
           ;; We're ready to interrogate the kernel pool for the
           ;; variables matching the template. gnpool tells us:
 
           ;;   1. Does the kernel pool contain any variables that
           ;;     match the template (value of found).
           ;;  2. If so, how many variables?
           ;;  3. The variable names. (cvals, an array of strings)
           ;;
 
           cspice_gnpool, tmplate, start, N_ITEMS, STRLEN, cvals, found
 
           if ( found) then begin
              print, "No. variables matching template: ", n_elements(cvals)
           endif else begin
              print, "No kernel variables matched template"
           stop
           endelse
 
           ;;
           ;; Okay, now we know something about the kernel pool
           ;; variables of interest to us. Let's find out more...
           ;;
           for i=0, (n_elements(cvals)-1) do begin
 
              ;;
              ;; Use dtpool to return the dimension and type,
              ;; C (character) or N (numeric), of each pool
              ;; variable name in the cvals array.
              ;;
              cspice_dtpool, cvals[i], found, dim, type
              print, cvals[i]
              print, " No. items: " + string(dim) + " Of type: " + type
 
              ;;
              ;; Test character equality, 'N' or 'C'.
              ;;
              case type of
 
                 'N': begin
 
                       ;;
                       ;; If 'type' equals 'N', we found a numeric array.
                       ;; In this case any numeric array will be an array
                       ;; of double precision numbers ("doubles").
                       ;; cspice_gdpool retrieves doubles from the
                       ;; kernel pool.
                       ;;
                       cspice_gdpool, cvals[i], start, N_ITEMS, dvars, $
                                                                found
 
                       for j=0, (n_elements(dvars)-1) do begin
 
                          print, "  Numeric value: ", dvars[j]
 
                       endfor
 
                    end
 
                 'C': begin
 
                       ;;
                       ;; If 'type' equals 'C', we found a string array.
                       ;; gcpool retrieves string values from the
                       ;; kernel pool.
                       ;;
                       cspice_gcpool, cvals[i], start, N_ITEMS, STRLEN, $
                                                          cvars, found
 
                       for j=0, (n_elements(cvars)-1) do begin
 
                          print, "  String value : ", cvars[j]
 
                       endfor
 
              end
 
              endcase
 
              print
 
           endfor
 
           ;;
           ;; Now look at the time variable EXAMPLE_TIMES. Extract this
           ;; value as an array of doubles.
           ;;
           cspice_gdpool, "EXAMPLE_TIMES", start, N_ITEMS, dvars, found
 
           print, "EXAMPLE_TIMES"
 
           for j=0, (n_elements(dvars)-1) do begin
 
              print, FORMAT='(A14,F24.5)', "  Time value: ", dvars[j]
 
           endfor
 
        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 cspice_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 cspice_dtpool loop, a
     second loop outputs the contents of the data variable using
     cspice_gcpool or cspice_gdpool.
 
 
         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 ICY 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
--------------------------------------------------------
 
         --   cspice_latrec, latitudinal to rectangular
 
         --   cspice_latcyl, latitudinal to cylindrical
 
         --   cspice_latsph, latitudinal to spherical
 
         --   cspice_reccyl, rectangular to cylindrical
 
         --   cspice_recgeo, rectangular to geodetic
 
         --   cspice_reclat, rectangular to latitudinal
 
         --   cspice_recsph, rectangular to spherical
 
         --   cspice_recrad, rectangular to right ascension - declination
 
         --   cspice_sphrec, spherical to rectangular
 
         --   cspice_sphcyl, spherical to cylindrical
 
         --   cspice_sphlat, spherical to latitudinal
 
         --   cspice_cyllat, cylindrical to latitudinal
 
         --   cspice_cylsph, cylindrical to spherical
 
         --   cspice_cylrec, cylindrical to rectangular
 
         --   cspice_georec, geodetic to rectangular
 
     As of Icy 1.1, the following routines allow vectorized arguments:
 
         --   cspice_latrec
 
         --   cspice_reccyl
 
         --   cspice_recgeo
 
         --   cspice_reclat
 
         --   cspice_recsph
 
         --   cspice_recrad
 
         --   cspice_sphrec
 
         --   cspice_cylrec
 
         --   cspice_georec
 
 
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
--------------------------------------------------------
 
 
        PRO COORD
 
           ;;
           ;; Define the inertial and non inertial frame names.
           ;;
           ;; Initialize variables or set type. All variables
           ;; used in a PROMPT construct must be initialized
           ;; as strings.
           ;;
           INRFRM = "J2000"
           NONFRM = "IAU_EARTH"
           timstr = ''
 
           ;;
           ;; Load the needed kernels using a cspice_furnsh call on the
           ;; meta kernel.
           ;;
           cspice_furnsh, "meta.ker"
 
           ;;
           ;; Prompt the user for a time string. Convert the
           ;; time string to ephemeris time J2000 (ET).
           ;;
           read, timstr, PROMPT = "Time of interest: "
           cspice_str2et,  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.
           ;;
           cspice_bodvrd, "EARTH", "RADII", 3, rad
 
           ;;
           ;; Calculate the flattening factor for the Earth.
           ;;
           ;;          equatorial_radius - polar_radius
           ;; flat =   ________________________________
           ;;
           ;;                equatorial_radius
           ;;
           flat = (rad[0] - rad[2])/rad[0];
 
           ;;
           ;; Make the cspice_spkpos call to determine the apparent
           ;; position of the Moon w.r.t. to the Earth at 'et' in the
           ;; inertial frame.
           ;;
           cspice_spkpos,  "MOON", et, INRFRM, "LT+S","EARTH", pos, ltime
 
           ;;
           ;; Show the current frame and time.
           ;;
           print, " Time : "         , timstr
           print, "  Inertial Frame: ", inrfrm
 
           ;;
           ;; First convert the position vector
           ;; X = pos[0], Y = pos[1], Z = pos[2], to RA/DEC.
           ;;
           cspice_recrad,  pos, range, ra, dec
           print, "   Range/Ra/Dec"
           print, "    Range: ", range
           print, "    RA   : ", ra * cspice_dpr()
           print, "    DEC  : ", dec* cspice_dpr()
 
           ;;
           ;; ...latitudinal coordinates...
           ;;
           cspice_reclat,  pos, range, lon, lat
           print, "   Latitudinal"
           print, "    Rad  : ", range
           print, "    Lon  : ", lon * cspice_dpr()
           print, "    Lat  : ", lat * cspice_dpr()
 
           ;;
           ;; ...spherical coordinates use the colatitude,
           ;; the angle from the Z axis.
           ;;
           cspice_recsph,  pos, range, colat, lon
           print, "   Spherical"
           print, "    Rad  : ", range
           print, "    Lon  : ", lon   * cspice_dpr()
           print, "    Colat: ", colat * cspice_dpr()
 
 
           ;;
           ;; Make the cspice_spkpos call to determine the apparent
           ;; position of the Moon w.r.t. to the Earth at 'et' in the
           ;; non-inertial, body fixed, frame.
           ;;
           cspice_spkpos,  "MOON", et, nonfrm, "LT+S","EARTH", pos, ltime
 
           print
           print, "  Non-inertial Frame: " + nonfrm
 
           ;;
           ;; ...latitudinal coordinates...
           ;;
           cspice_reclat,  pos, range, lon, lat
           print, "   Latitudinal "
           print, "    Rad  : ", range
           print, "    Lon  : ", lon * cspice_dpr()
           print, "    Lat  : ", lat * cspice_dpr()
 
           ;;
           ;; ...spherical coordinates...
           ;;
           cspice_recsph,  pos, range, colat, lon
           print, "   Spherical"
           print, "    Rad  : ", range
           print, "    Lon  : ", lon   * cspice_dpr()
           print, "    Colat: ", colat * cspice_dpr()
 
           ;;
           ;; ...finally, convert the position to geodetic coordinates.
           ;;
           cspice_recgeo,  pos, rad[0], flat, lon, lat, range
           print, "   Geodetic"
           print, "    Rad  : ", range
           print, "    Lon  : ", lon * cspice_dpr()
           print, "    Lat  : ", lat * cspice_dpr()
           print
 
        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:        369340.82
            RA   :        203.64369
            DEC  :       -4.9790104
 
 
     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  :        369340.82
            Lon  :       -156.35631
            Lat  :       -4.9790104
 
 
     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  :        369340.82
            Lon  :       -156.35631
            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  :        369340.82
            Lon  :        70.973950
            Lat  :       -4.9896751
 
 
     Spherical.
 
           Spherical
            Rad  :        369340.82
            Lon  :        70.973950
            Colat:        94.989675
 
 
     Geodetic. The cartographic lat/lon.
 
 
           Geodetic
            Rad  :        362962.84
            Lon  :        70.973950
            Lat  :       -4.9902493
 
 
 
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 ICY.
 
 
Relevant Routines
--------------------------------------------------------
 
         --   cspice_str2et converts time strings to ephemeris time (ET).
 
         --   cspice_timout formats a time string output.
 
         --   cspice_tpictr creates a format template for use in
              cspice_timout.
 
         --   cspice_tsetyr sets the reference century/year for two digit
              representation of the year.
 
     As of Icy 1.1, the following routines allow vectorized arguments:
 
         --   cspice_str2et
 
         --   cspice_timout
 
 
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 cspice_timout for a list of the string
     markers used by cspice_timout and cspice_tpictr to describe time
     string format. Always keep in mind cspice_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 ICY-supported formats.
 
 
Code Solution
--------------------------------------------------------
 
     Caution: Be sure to assign sufficient string lengths for time
     formats/pictures.
 
 
        PRO TIC
 
           ;;
           ;; Assign the LSK variable to the name of the leapsecond,
           ;; kernel and create an arbitrary time string.
           ;;
           ;; Define the maximum length for any string, 80
           ;; characters plus one null terminator for C.
           ;;
           CALSTR   = "Mar 15, 2003 12:34:56.789 AM PST";
           LSK      = "kernels/lsk/leapseconds.tls";
           AMBIGSTR = "Mar 15, 79 12:34:56";
           STRLEN   = 81
 
           ;;
           ;; Load the leapseconds kernel.
           ;;
           cspice_furnsh, LSK
           print, "Original time string       : " + 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).
           ;;
           cspice_str2et, CALSTR, et
           print, "Corresponding ET           : ", et
 
           ;;
           ;; Make a picture of an output format. Describe a Unix-like
           ;; time string then send the picture and the 'et' value through
           ;; cspice_timout to format and convert the ET representation
           ;; of the time string into the form described in cspice_timout.
           ;; 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.
 
           ;;
           cspice_timout, et, 'Wkd Mon DD HR:MN:SC PDT YYYY ::UTC-7', $
                                                         STRLEN, timstr
           print, "Time in string format 1    : " + timstr
 
           ;;
           ;; Create another picture, this time combine a calendar,
           ;; 2 digit year , with Julian Day format.
           ;;
           cspice_timout, et,                                     $
             'Wkd Mon DD HR:MN ::UTC-7 YR (JULIAND.##### JDUTC)', $
              STRLEN, timstr
           print, "Time in string format 2    : " + timstr
 
           ;;
           ;; Why create a picture by hand when Icy can do it for you?
           ;; Input a string to cspice_tpictr 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 the picture
           ;; string is known as correct..
           ;;
           cspice_tpictr, '12:34:56.789 P.M. PDT January 1, 2006', $
                           STRLEN, pictr, ok, error
 
           if ( NOT ok ) then begin
              print, 'ERROR from cspice_tpictr: ' + error
              stop
           endif
 
           cspice_timout, et, pictr, STRLEN, timstr
           print, "Time in string format 3    : " + timstr
 
           ;;
           ;; Two digit year representations often cause problems due to
           ;; the ambiguity of the century. The routine cspice_tsetyr 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.
           ;;
           cspice_str2et, AMBIGSTR, et1
 
           ;;
           ;; Set 1980 as the base year causes SPICE to interpret the
           ;; time string's "79" as 2079.
           ;;
           cspice_tsetyr, 1980
           cspice_str2et, AMBIGSTR, et2
 
           ;;
           ;; Calculate the number of years between the two ET
           ;; representations, ~100.
           ;;
           print, "Years between evaluations  :  ", $
                           (et2 - et1)/cspice_jyear()
 
           ;;
           ;; Reset the default year to 1969 so other scripts use the
           ;; default.
           ;;
           cspice_tsetyr, 1969
 
        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: 100.000000
 
 
 
Lesson 5: Error Handling
===========================================================================
 
     Lesson Goal:
 
     The Icy error subsystem differs from other SPICE packages in that the
     user cannot alter the state of the subsystem, rather the user can
     respond to an error signal using the "catch" function. This function
     natively receives and processes any SPICE error signaled from Icy. The
     user can therefore "catch" an error signal so as to respond in an
     appropriate manner.
 
 
Relevant Routines:
--------------------------------------------------------
 
         --   "catch" sets an IDL error handler flagging an error signal in
              the current procedure. The mechanism operates like
              setjump/longjump, or catch/throw.
 
         --   "catch, \cancel" deletes an IDL error handler.
 
 
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
--------------------------------------------------------
 
     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
--------------------------------------------------------
 
 
        PRO ADDERR
 
           ;;
           ;; Set initial parameters.
           ;;
           SPICETRUE = 1L
           SPICEFALSE= 0L
           doloop    = SPICETRUE;
 
           ;;
           ;; Load the data we need for state evaluation.
           ;;
           cspice_furnsh, "meta.ker"
 
           ;;
           ;; Start our input query loop to the user.
           ;;
           while (doloop) do begin
 
              ;;
              ;; Initialize the input value as a string. YOU MUST
              ;; do this to use PROMPT in a read.
              ;;
              targ = ''
 
              ;;
              ;; 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).
              ;;
              read, targ, PROMPT= "Target: "
 
              if cspice_eqstr( targ, "NONE") then begin
 
                 ;;
                 ;; An exit condition. If the user inputs NONE
                 ;; for a target name, set the loop to stop...
                 ;;
                 doloop = SPICEFALSE;
 
              endif else begin
 
                 ;;
                 ;; ...otherwise evaluate the state between the Earth
                 ;; and the target. Initialize an error handler.
                 ;;
                 catch, err
 
                 ;;
                 ;; What if the program can't perform the evaluation?
                 ;; Then ICY sets an error message informing
                 ;; the user of the problem's cause.
                 ;;
                 ;; Examine the value of 'err' to determine if we
                 ;; output a state vector or not.
                 ;;
                 if ( err ne 0 ) then begin
 
                    ;;
                    ;; Error signal detected. Output the error response
                    ;; information.
                    ;;
                    print, !error_state.name
                    print, !error_state.msg
                    print
 
                 endif else begin
 
                    ;;
                    ;; Perform the state lookup. If an error occurs,
                    ;; program flow returns the first line after the
                    ;; "catch, err"; in that case, 'err' will have a
                    ;; non-zero value.
                    ;;
                    cspice_spkezr, targ, 0.d, "J2000", "LT+S", "EARTH", $
                                   state, ltime
 
                    ;;
                    ;; No error, output the state.
                    ;;
                    print, FORMAT = '( "R : ", 3F17.5)', state[0:2];
                    print, FORMAT = '( "V : ", 3F17.5)', state[3:5];
                    print, "LT: ", ltime
                    print
 
                 endelse
 
                catch, /cancel
 
              endelse
 
           endwhile
 
           ;;
           ;; Done. Unload the kernels.
           ;;
           cspice_unload, "meta.ker"
 
        END
 
 
 
Run the code example
 
     Now run the code with various inputs to observe behavior. Begin the
     run using known astronomical bodies. Recall the ICY 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:        1.3423106
 
        Target: Mars
        R :   234536077.41914 -132584383.59557  -63102685.70619
        V :          30.95976         28.93646         13.11449
        LT:        923.00108
 
        Target: Pluto barycenter
        R : -1451304742.83853-4318174144.40632 -918251433.58736
        V :          35.03838          3.06560         -0.01514
        LT:        15501.258
 
        Target: Puck
        ICY_M_SPICE_ERROR
        CSPICE_SPKEZR: SPICE(SPKINSUFFDATA): [spkezr_c->SPKEZR->SPKEZ->
                         SPKAPP->SPKSSB->SPKGEO] 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.
 
 
     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).
 
     Try another look-up.
 
 
        Target: Casper
        ICY_M_SPICE_ERROR
        CSPICE_SPKEZR: SPICE(IDCODENOTFOUND): [spkezr_c->SPKEZR] 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'
 
 
     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:        567.65507
 
 
     The look-up succeeded despite two errors in our run. The ICY 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 ICY data types 'cell' and
     'window. A 'cell' is as the basis for set calculations in ICY. 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
--------------------------------------------------------
 
         --   cspice_celld, create a cell for double precision data
 
         --   cspice_wncomd determines the compliment of a window with
              respect to a defined interval.
 
         --   cspice_wncond contracts a window's intervals.
 
         --   cspice_wndifd : Calculate the difference between two windows;
              i.e. every point existing in the first but not the second.
 
         --   cspice_wnelmd returns TRUE or FALSE if a value exists in a
              window.
 
         --   cspice_wnexpd expands the size of the intervals in a window.
 
         --   cspice_wnextd extracts a window's endpoints .
 
         --   cspice_wnfetd retrieves a specified interval from a window.
 
         --   cspice_wnfild fills gaps between intervals in a window.
 
         --   cspice_wnfltd filter/removes small intervals from a window.
 
         --   cspice_wnincd determines if an interval exists within a
              window.
 
         --   cspice_wninsd inserts an interval into a window.
 
         --   cspice_wnintd calculates the intersection of two windows.
 
         --   cspice_wnreld compares two windows. Comparison operations
              available, equality '=', inequality '<>', subset '<=' and
              '>=', proper subset '<' and '>'.
 
         --   cspice_wnsumd creates a window summary.
 
         --   cspice_wnunid calculates the union of two windows.
 
         --   cspice_wnvald validates/creates a window from a cell array.
 
 
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
--------------------------------------------------------
 
        PRO WIN
 
           ;;
           ;; Define the cells to use as windows.
           ;; The windows can hold 8 data values i.e.
           ;; four intervals.
           ;;
           MAXSIZ = 8
           loswin = cspice_celld( MAXSIZ )
           phswin = cspice_celld( MAXSIZ )
           sched  = cspice_celld( MAXSIZ )
 
           ;;
           ;; Define a set 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.
           ;;
           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" ]
 
           ;;
           ;; A second set of intervals representing the times for which
           ;; an acceptable phase angle exits between the ground station,
           ;; the body and the Sun.
           ;;
           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" ]
 
           ;;
           ;; Load our meta kernel for the leapseconds data.
           ;;
           cspice_furnsh, "meta.ker"
 
           ;;
           ;; SPICE windows consist of double precision values; convert
           ;; the string time tags defined in the 'los'and 'phase'
           ;; arrays to double precision ET. Store the double values
           ;; in the 'loswin' and 'phswin' windows.
           ;;
           cspice_str2et, los  , los_et
           cspice_str2et, phase, phs_et
 
           ;;
           ;; Initialize the cells from the double precision arrays,
           ;; then validate the cells as windows.
           ;;
           for i=0, (MAXSIZ/2) -1 do begin
                 cspice_wninsd, los_et[i*2], los_et[i*2 + 1], loswin
                 cspice_wninsd, phs_et[i*2], phs_et[i*2 + 1], phswin
           endfor
 
           cspice_wnvald, MAXSIZ, MAXSIZ, loswin
           cspice_wnvald, MAXSIZ, MAXSIZ, phswin
           cspice_wnvald, 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,
           ;; (the intersection of the time intervals)
           ;; place the results in the window 'sched'.
           ;;
           cspice_wnintd, loswin, phswin, 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.
           ;;
 
           print
           print, "No. data values in sched            : ",            $
                                                      cspice_card(sched)
           print, "Space available for values in sched : ",            $
                                                      cspice_size(sched)
           print
           print, "Time intervals meeting defined criterion."
 
           for i=0, (cspice_card(sched)/2)-1 do begin
 
              ;;
              ;; Extract from the derived 'sched' the values defining the
              ;; time intervals.
              ;;
              cspice_wnfetd, sched, i, left, right
 
              ;;
              ;; Convert the ET values to UTC for human comprehension.
              ;;
              cspice_et2utc, left , "C", 3, utcstr_l
              cspice_et2utc, right, "C", 3, utcstr_r
 
              ;;
              ;; Output the UTC string and the corresponding index
              ;; for the interval.
              ;;
              print, i, " ", utcstr_l, utcstr_r
 
           endfor
 
 
           ;;
           ;; Summarize the 'sched' window.
           ;;
           cspice_wnsumd, sched, meas, avg, stddev, small, large
 
           print
           print, "Summary of sched window"
 
           print, "o Total measure of sched    : ", meas
           print, "o Average measure of sched  : ", avg
           print, "o Standard deviation of "
           print, "  the measures in sched     : ", stddev
 
           ;;
           ;; The values for small and large refer to the indexes of the
           ;; values in the window ('sched'). The shortest interval is
           ;;
           ;;      [ sched.base[ sched.data + small]
           ;;        sched.base[ sched.data + small +1]  ];
           ;;
           ;; the longest is
           ;;
           ;;      [ sched.base[ sched.data + large]
           ;;        sched.base[ sched.data + large +1]  ];
           ;;
           ;; Output the interval indexes for the shortest and longest
           ;; intervals. As IDL bases an array index on 0, the interval
           ;; index is half the array index.
           ;;
           print, "o Index of shortest interval: ", small/2
           print, "o Index of longest interval : ", large/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.
               0 2003 JAN 02 00:03:30.0002003 JAN 02 04:43:29.000
               1 2003 JAN 05 12:00:00.0002003 JAN 05 12:45:00.000
               2 2003 JAN 06 00:30:00.0002003 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    :        25980.000
        o Average measure of sched  :        8660.0000
        o Standard deviation of
          the measures in sched     :        5958.5502
        o Index of shortest interval:            1
        o Index of longest interval :            0
 
 
 
Lesson 7: Utility and Constants Routines
===========================================================================
 
     Lesson Goals:
 
     ICY 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.
 
     ICY also includes a set of functions that return constant values often
     used in astrodynamics, time calculations, and geometry.
 
 
Relevant Routines
--------------------------------------------------------
 
         --   cspice_convrt converts between measurements units
 
         --   cspice_tkvrsn returns the current version of the toolkit
 
         --   cspice_eqstr returns a boolean describing the equality of two
              strings. The comparison is case insensitive and ignores
              spaces.
 
         --   cspice_exists returns a boolean indicating the existence of a
              file.
 
         --   cspice_clight : velocity of light in a vacuum, kilometers per
              second
 
         --   cspice_dpr : number of degrees per radian (180/Pi)
 
         --   cspice_rpd : number radians per degree (Pi/180)
 
         --   cspice_spd : number of seconds per day (60*60*24)
 
         --   cspice_b1900 : Julian Date of the epoch Besselian Date 1900.0
 
         --   cspice_b1950 : Julian date of the epoch Besselian Date 1950.0
 
         --   cspice_j1900 : Julian date of 1900 JAN 0.5 (1899 DEC 31
              12:00:00)
 
         --   cspice_j1950 : Julian date of 1950 JAN 1.0 (1950 JAN 1
              00:00:00)
 
         --   cspice_j2000 : Julian date of 2000 JAN 1.5 (2000 JAN 1
              12:00:00)
 
         --   cspice_j2100 : Julian date of 2100 JAN 1.5 (2100 JAN 1
              12:00:00)
 
         --   cspice_twopi : double precision value of 2 * Pi
 
         --   cspice_pi : double precision value of Pi
 
         --   cspice_halfpi : double precision value of 0.5 * Pi
 
         --   cspice_jyear : seconds per Julian year (365.25 Julian days)
 
         --   cspice_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
--------------------------------------------------------
 
 
        PRO UNITS
 
           ;;
           ;; Initialize variables. All variables used in a PROMPT
           ;; construct must be initialized as strings.
           ;;
           funits  = ''
           fromstr = ''
           tunits  = ''
 
           ;;
           ;; Display the Toolkit version string with a
           ;; cspice_tkvrsn call.
           ;;
           vers = cspice_tkvrsn( "TOOLKIT" )
           print, "Convert demo program compiled against CSPICE Toolkit " $
                  + vers
 
           ;;
           ;; The user first inputs the name of a unit of measure.
           ;; Send the name through TOSTAN for de-aliasing.
           ;;
           read, funits, PROMPT= "From Units : "
           tostan, funits
 
           ;;
           ;; Input a double precision value to express in a new
           ;; unit format.
           ;;
           read, fromstr, PROMPT = "From Value : "
           cspice_prsdp, fromstr, fvalue
 
           ;;
           ;; Now the user inputs the name of the output units.
           ;; Again we send the units name through TOSTAN for
           ;; de-aliasing.
           ;;
           read, tunits, PROMPT = "To Units   : "
           tostan, tunits
 
           cspice_convrt, fvalue, funits, tunits, tvalue
           print,  tvalue, " ", tunits
 
        END
 
        PRO TOSTAN, alias
 
           ;;
           ;; As a convenience, let's alias a few common terms
           ;; to their appropriate counterpart. Use cspice_eqstr
           ;; to compare strings. The comparison ignores
           ;; letter case and trailing/leading spaces. NOTE: the SWITCH
           ;; statement performs the same function as the multiple
           ;; "if" blocks. SWITCH was not used in order to demonstrate
           ;; the cspice_eqstr call.
           ;;
 
           if ( cspice_eqstr( alias, "meter") ) then begin
 
                 ;;
                 ;; First, a 'meter' by any other name is a
                 ;; 'METER' and smells as sweet ...
                 ;;
                 alias = "METERS"
           endif
 
           if ( cspice_eqstr( alias, "clicks"    ) OR $
                cspice_eqstr( alias, "kilometers") OR $
                cspice_eqstr( alias, "kilometer" )     ) then begin
 
                 ;;
                 ;; ... 'clicks' and 'KILOMETERS' and 'KILOMETER'
                 ;; identifies 'KM'....
                 ;;
                 alias = "KM"
           endif
 
           if ( cspice_eqstr( alias, "secs") ) then begin
 
                 ;;
                 ;; ... 'secs' to 'SECONDS'.
                 ;;
                 alias = "SECONDS"
           endif
 
           if ( cspice_eqstr( alias, "miles") ) then begin
 
                 ;;
                 ;; ... 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.
                 ;;
                 alias = "STATUTE_MILES"
           endif
 
           ;;
           ;; Much better. Now return. If the input matched
           ;; none of the aliases, this routine did nothing.
           ;;
 
        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 CSPICE Toolkit CSPICE_N0057
        >From Units : clicks
        >From Value : 3
        To Units   : miles
               1.8641136 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?
 
 
        Convert demo program compiled against CSPICE Toolkit CSPICE_N0057
        >From Units : miles
        >From Value : 26.2
        To Units   : km
               42.164813 km
 
 
 
Programming Task
--------------------------------------------------------
 
     Write a program to output ICY constants and use those constants to
     calculate some rudimentary values.
 
 
Code Solution
--------------------------------------------------------
 
 
        PRO CONST
 
           ;;
           ;; All the function have the same calling sequence:
           ;;
           ;;    VALUE = function_name()
           ;;
           ;;    some_procedure( function_name() )
           ;;
           ;;    print, function_name()
           ;;
           ;; First a simple example using the seconds per day
           ;; constant...
           ;;
           print,   $
           FORMAT = $
           '("Number of (S)econds (P)er (D)ay           : ", F19.12)',$
                                                            cspice_spd()
 
           ;;
           ;; ...then show the value of degrees per radian, 180/Pi...
           ;;
           print,   $
           FORMAT = $
           '("Number of (D)egrees (P)er (R)adian        : ", F19.16)',$
                                                            cspice_dpr()
 
           ;;
           ;; ...and the inverse, radians per degree, Pi/180.
           ;; It is obvious cspice_dpr() equals 1.d/cspice_rpd(), or
           ;; more simply cspice_dpr() * cspice_rpd() equals 1
           ;;
           print,   $
           FORMAT = $
           '("Number of (R)adians (P)er (D)egree        : ", F19.16)',$
                                                            cspice_rpd()
 
           ;;
           ;; What's the value for the astrophysicist's favorite
           ;; physical constant (in a vacuum)?
           ;;
           print,   $
           FORMAT = $
           '("Speed of light in KM per second           : ", F19.12)',$
                                                        cspice_clight()
 
           ;;
           ;; How long (in Julian days) from the J2000 epoch to the
           ;; J2100 epoch?
           ;;
           print, "Number of days between epochs J2000 and     "
           print, $
           FORMAT = $
           '("  J2100                                   : ", F19.12)',$
                                        cspice_j2100() - cspice_j2000()
 
           ;;
           ;; Redo the calculation returning seconds...
           ;;
           print, "Number of seconds between epochs J2000 "
           print,   $
           FORMAT = $
           '("   and J2100                              : ", F19.5)',$
                     cspice_spd() * (cspice_j2100() - cspice_j2000() )
 
           ;;
           ;; ...then tropical years.
           ;;
           print,  "Number of tropical years between epochs     "
           print, $
           FORMAT = $
           '("  J2000 and J2100                         : ", F19.12)',$
                                   ( cspice_spd() / cspice_tyear() )  $
                                * (cspice_j2100() - cspice_j2000() )
 
           ;;
           ;; Finally, how can I convert a radian value to degrees.
           ;;
           print,   $
           FORMAT = $
           '("Number of degrees in Pi/2 radians of arc  : ", F19.16)',$
                                         cspice_halfpi() * cspice_dpr()
 
           ;;
           ;; and degrees to radians.
           ;;
           print,   $
           FORMAT = $
           '("Number of radians in 250 degrees of arc   : ", F19.16)',$
                                                   250.D * cspice_rpd()
 
        END
 
 
 
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
 
 
