Main Page Preface - Other Stuff (The Red Shirt topics) (IDL)
## Table of Contents
       Preface - Other Stuff (The Red Shirt topics) (IDL)
       Coding and Use Lessons
          Note About HTML Links
          NAIF Documentation
             Required Reading and Users Guides
             Library Source Code Documentation
             API Documentation
             Tutorials
          Text kernels
             Text kernel format
          Kernels for lessons
             Input kernel files
             Output
       Lesson 1: Kernel Management with the Kernel Subsystem
          Relevant Routines
          Requirements and References
          Programming Task
          Code Solution
             First, create a meta text kernel:
             Now the solution source code:
             Run the code example
       Lesson 2: The Kernel Pool
          Relevant Routines
          Requirements and References
          Programming Task
          Code Solution
             Run the code example
       Lesson 3: Coordinate Conversions
          Relevant Routines
          Requirements and References
          Programming Task
          Code Solution
             Run the code example
       Lesson 4: Advanced Time Manipulation Routines
          Relevant Routines
          Requirements and References
          Programming Task
          Code Solution
             Run the code example
       Lesson 5: Error Handling
          Relevant Routines:
          Requirements and References
          Programming Task
          Code Solution
             Run the code example
       Lesson 6: Windows, and Cells
          Relevant Routines
          Requirements and References
          Programming task:
          Code Solution
             Run the code example
       Lesson 7: Utility and Constants Routines
          Relevant Routines
          Requirements and References
          Programming Task
          Code Solution
             Run the code example
          Programming Task
          Code Solution
             Run the code example
Top # Preface - Other Stuff (The Red Shirt topics) (IDL) October 20, 2008 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 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. Top # Coding and Use Lessons This workbook contains 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 and Cells `7.` Utility and Constants Routines Top ## 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. Top ## 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, IDL, or MATLAB 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 `--` Library Source Code Documentation `--` API Documentation `--` Tutorials Top ### Required Reading and Users Guides NAIF Required Reading (*.req) documents introduce the functionality of particular Icy 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 Icy 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:
          ../icy/doc/
HTML format documentation The Icy distributions include HTML versions of Required Readings and Users Guides, accessible from the HTML documentation directory:
         ../icy/doc/html/index.html
Top ### 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 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:
          ../icy/src/
Find the CSPICE library source code in:
          ../icy/src/cspice/
Note: The CSPICE source files have two forms: C files created by the f2c conversion process on a SPICELIB files, indicated with a name of the form "module.c," and wrappers files indicated by names of the form "module_c.c" The f2c converted source code is very difficult to read, refer to the wrapper routines if possible. In some cases, NAIF replaced an f2c converted file with a hand written version. Top ### 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 and links to the wrapper source code.
          ...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
Top ### 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. Top ## 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. Top ### 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. Top ## Kernels for lessons Top ### 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/
Top ### 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. Top # 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. Top ## 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 and deletes any pool variables defined by that kernel from the kernel subsystem. `--` cspice_kclear deletes all kernel pool data from the kernel subsystem. Top ## Requirements and References Knowledge of information in the kernels.req document, the mk.ppt and intro_to_kernels.ppt tutorial files. Top ## 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. Top ## Code Solution Top ### 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
Top ### Now the solution source code:
       PRO KERNEL

          ;;
          ;; Assign the path name of the meta kernel to META.
          ;;
          META = 'meta.tm'

          ;;
          ;; 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
Top ### 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.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
Top # 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.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
Top ## 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. Top ## 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 API documentation for the particular routines. Top ## 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. Top ## 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.tm'

          ;;
          ;; Initialize the start value. This values indicates
          ;; index of the first element to return if a kernel
          ;; variable is an array. START = 0 indicates return everything.
          ;; START = 1 indicates return everything but the first element.
          ;;
          START = 0;

          ;;
          ;; Set the template for the variable names to find. Let's
          ;; look for all variables containing  the string RING.
          ;; Define this with the wildcard template '*RING*'. Note:
          ;; the template '*RING' would match any variable name
          ;; ending with the RING string.
          ;;
          tmplate = '*RING*'

          ;;
          ;; We're ready to interrogate the kernel pool for the
          ;; variables matching the template. cspice_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=0L, (n_elements(cvals)-1L) 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 m=0L, (n_elements(dvars)-1L) do begin

                         print, '  Numeric value: ', dvars[m]

                      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=0L, (n_elements(cvars)-1L) 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=0L, (n_elements(dvars)-1L) do begin

             print, FORMAT='(A14,F24.6)', '  Time value: ', dvars[j]

          endfor

          ;;
          ;; Done. Unload the kernels.
          ;;
          cspice_kclear

       END
Top ### 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:        122170.00
         Numeric value:        136780.00
         Numeric value:       0.10000000
         Numeric value:       0.10000000
         Numeric value:       0.50000000

       BODY699_RING2
        No. items:            5 Of type: N
         Numeric value:        117580.00
         Numeric value:        122170.00
         Numeric value:        0.0000000
         Numeric value:        0.0000000
         Numeric value:        0.0000000

       BODY699_RING1_1
        No. items:            5 Of type: N
         Numeric value:        133405.00
         Numeric value:        133730.00
         Numeric value:        0.0000000
         Numeric value:        0.0000000
         Numeric value:        0.0000000

       BODY699_RING1_NAME
        No. items:            1 Of type: C
         String value : A Ring

       BODY699_RING2_NAME
        No. items:            1 Of type: C
         String value : Cassini Division

       BODY699_RING1_1_NAME
        No. items:            1 Of type: C
         String value : Encke Gap
Note the final time value differs from the previous values in the final three decimal places despite the intention that all three strings represent the same time. This results from round-off when converting a decimal Julian day representation to the seconds past J2000 ET representation.
       EXAMPLE_TIMES
         Time value:         134094896.789000
         Time value:         134094896.789000
         Time value:         134094896.789753
Top # 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. Top ## 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 Top ## 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. Top ## 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. Top ## 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.tm'

          ;;
          ;; 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
Top ### 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  :        70.986950
           Lat  :       -4.9896751
Spherical.
          Spherical
           Rad  :        369340.82
           Lon  :        70.986950
           Colat:        94.989675
Geodetic. The cartographic lat/lon.
          Geodetic
           Rad  :        362962.84
           Lon  :        70.986950
           Lat  :       -4.9902493
Top # 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. Top ## 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. Top ## 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. Top ## 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. Top ## 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

          ;;
          ;; Confirm the tpictr_c call succeeded. Report the error string
          ;; if not.
          ;;
          if ( ~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.
          ;;
          cspice_tsetyr, 1969

          ;;
          ;; Done. Unload the kernels.
          ;;
          cspice_kclear

       END
Top ### Run the code example
       Original time string      : Mar 15, 2003 12:34:56.789 AM PST
       Corresponding ET          :    1.0098936e+08
       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 :         100.00000
Top # Lesson 5: Error Handling Lesson Goal: The Icy error subsystem differs from CSPICE and SPICELIB packages in that the user cannot alter the state of the error 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. Top ## 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" cancels an IDL error handler. Top ## Requirements and References Knowledge of material in the error.req document and the exceptions.ppt tutorial file. Comprehension of the catch/throw concept. Top ## 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. Top ## Code Solution
       PRO ADERR

          ;;
          ;; Set initial parameters.
          ;;
          SPICETRUE = 1B
          SPICEFALSE= 0B
          doloop    = SPICETRUE;

          ;;
          ;; Load the data we need for state evaluation.
          ;;
          cspice_furnsh, 'meta.tm'

          ;;
          ;; 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_kclear

       END
Top ### 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.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). 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. Top # 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. An IDL SPICE cell consists of an IDL structure comprised of the same fields as a C SPICE cell. A user should create cells by use of the appropriate Icy 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. Top ## 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. Top ## Requirements and References Knowledge of cells.req, and windows.req documents, as well as the other_functions.ppt tutorial file. Top ## 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. Top ## 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.tm'

          ;;
          ;; 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=0L, (MAXSIZ/2L) -1L 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=0L, (cspice_card(sched)/2L)-1L 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/2L
          print, 'o Index of longest interval : ', large/2L

       END
Top ### Run the code example The output window has the name SCHED (schedule). Output the amount of data held in SCHED compared to the maximum possible amount.
        No. data values in SCHED            :   6
        Space available for values in SCHED :   8
List the time intervals for which a line of sight exists during the time of a proper phase angle.
       Time intervals meeting defined criterion.
              0 2003 JAN 02 00:03:30.000  2003 JAN 02 04:43:29.000
              1 2003 JAN 05 12:00:00.000  2003 JAN 05 12:45:00.000
              2 2003 JAN 06 00:30:00.000  2003 JAN 06 02:18:01.000
Finally, an analysis of the SCHED data. The measure of an interval [a,b] (a <= b) equals b-a. Real values output in units of seconds.
       Summary of sched window
       o Total measure of sched    :        25980.000
       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
Top # Lesson 7: Utility and Constants Routines Lesson Goals: Icy 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 Icy also includes a set of functions that return constant values often used in astrodynamics, time calculations, and geometry. Top ## 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 this corresponds to calendar date 1899 DEC 31 12:00:00 `--` cspice_j1950 : Julian date of 1950 JAN 1.0 this corresponds to calendar date 1950 JAN 01 00:00:00 `--` cspice_j2000 : Julian date of 2000 JAN 1.5 (2000 JAN 01 12:00:00) `--` cspice_j2100 : Julian date of 2100 JAN 1.5, this corresponds to calendar date 2100 JAN 01 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) Top ## 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. Top ## 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. Top ## 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, 'klicks'    ) OR $
               cspice_eqstr( alias, 'kilometers') OR $
               cspice_eqstr( alias, 'kilometer' )     ) then begin

                ;;
                ;; ... 'klicks' 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
Top ### Run the code example Run a few conversions through the application to ensure it works. The intro banner gives us the Toolkit version against which the application was linked:
       Convert demo program compiled against CSPICE Toolkit CSPICE_N0060
       From Units : klicks
       From Value : 3
       To Units   : miles
              1.8641136 STATUTE_MILES
Now we know. Three kilometers equals 1.864 miles. Legend states Pheidippides ran from the Marathon Plain to Athens. The modern marathon race (inspired by this event) spans 26.2 miles. How far in kilometers?
       Convert demo program compiled against CSPICE Toolkit CSPICE_N0060
       From Units : miles
       From Value : 26.2
       To Units   : km
              42.164813 km
Top ## Programming Task Write a program to output Icy constants and use those constants to calculate some rudimentary values. Top ## 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
Top ### 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