 
Remote Sensing Hands-On Lesson (FORTRAN)
===========================================================================
 
   February 8, 2010
 
 
Overview
--------------------------------------------------------
 
   In this lesson you will develop a series of simple programs that
   demonstrate the usage of SPICE to compute a variety of different
   geometric quantities applicable to experiments carried out by a remote
   sensing instrument flown on an interplanetary spacecraft. This
   particular lesson focuses on a framing camera flying on the Cassini
   spacecraft, but many of the concepts are easily extended and generalized
   to other scenarios.
 
 
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.
 
 
References
--------------------------------------------------------
 
 
Tutorials
 
   The following SPICE tutorials are referred to by the discussions in this
   lesson:
 
      Name             Lesson steps/routines it describes
      ---------------  -----------------------------------------
      Time             Time Conversion
      SCLK and LSK     Time Conversion
      SPK              Obtaining Ephemeris Data
      Frames           Reference Frames
      Using Frames     Reference Frames
      PCK              Planetary Constants Data
      CK               Spacecraft Orientation Data
 
   These tutorials are available from the NAIF ftp server at JPL:
 
      http://naif.jpl.nasa.gov/naif/tutorials.html
 
 
Required Readings
 
   The Required Reading documents are provided with the Toolkit and are
   located under the ``toolkit/doc'' directory in the FORTRAN installation
   tree.
 
      Name             Lesson steps/routines that it describes
      ---------------  -----------------------------------------
      time.req         Time Conversion
      sclk.req         SCLK Time Conversion
      spk.req          Obtaining Ephemeris Data
      frames.req       Using Reference Frames
      pck.req          Obtaining Planetary Constants Data
      ck.req           Obtaining Spacecraft Orientation Data
      naif_ids.req     Determining Body ID Codes
 
 
The Permuted Index
 
   Another useful document distributed with the Toolkit is the permuted
   index. This is located under the ``toolkit/doc'' directory in the
   FORTRAN installation tree.
 
   This text document provides a simple mechanism to discover what SPICE
   routines perform a particular function of interest as well as the name
   of the source module that contains the routine. This is particularly
   useful for FORTRAN programmers because some of the routines are entry
   points and, therefore, the name does not translate directly into the
   name of the source module that contains them.
 
 
Source Code Header Comments
 
   The most detailed specification of a given SPICE FORTRAN or C routine is
   contained in the header section of its source code. The source code is
   distributed with the Toolkit and is located under
   ``toolkit/src/spicelib'' in FORTRAN and under ``cspice/src/cspice'' in C
   Toolkits.
 
   For example the source code of the STR2ET/str2et_c routine is
 
      toolkit/src/spicelib/str2et.for
 
   in the FORTRAN Toolkit and in
 
      cspice/src/cspice/str2et_c.c
 
   in the C Toolkit.
 
   Since some of the FORTRAN routines are entry points they are usually
   part of a source file that has different name. The ``Permuted Index''
   document mentioned above can be used to locate the name of their source
   file.
 
 
Kernels Used
--------------------------------------------------------
 
   The following kernels are used in examples provided in this lesson:
 
      #  FILE NAME                 TYPE  DESCRIPTION
      -- ------------------------- ----  ------------------------
      1  naif0008.tls              LSK   Generic LSK
      2  cas00084.tsc              SCLK  Cassini SCLK
      3  981005_PLTEPH-DE405S.bsp  SPK   Solar System Ephemeris
      4  020514_SE_SAT105.bsp      SPK   Saturnian Satellite Ephemeris
      5  030201AP_SK_SM546_T45.bsp SPK   Cassini Spacecraft SPK
      6  cas_v37.tf                FK    Cassini FK
      7  04135_04171pc_psiv2.bc    CK    Cassini Spacecraft CK
      8  cpck05Mar2004.tpc         PCK   Cassini Project PCK
      9  cas_iss_v09.ti            IK    ISS Instrument Kernel
 
   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/
 
 
SPICE Modules Used
--------------------------------------------------------
 
   This section provides a complete summary of the routines, and the
   kernels that are suggested for usage in each of the exercises in this
   tutorial. (You may wish to not look at this list unless/until you ``get
   stuck'' while working on your own.)
 
      CHAPTER EXERCISE   ROUTINES   FUNCTIONS  KERNELS
      ------- ---------  ---------  ---------  ---------
        1     convtm     FURNSH                1,2
                         PROMPT
                         STR2ET
                         ETCAL
                         TIMOUT
                         SCE2C
                         SCE2S
 
        2     getsta     FURNSH     VNORM      1,3-5
                         PROMPT
                         STR2ET
                         SPKEZR
                         SPKPOS
                         CONVRT
 
        3     xform      FURNSH     VSEP       1-8
                         PROMPT
                         STR2ET
                         SPKEZR
                         SXFORM
                         MXVG
                         SPKPOS
                         PXFORM
                         MXV
                         CONVRT
 
        4     subpts     FURNSH                1,3-5,8
                         PROMPT
                         STR2ET
                         SUBPT
                         SUBSOL
 
        5     fovint     FURNSH     DPR        1-9
                         PROMPT
                         STR2ET
                         BODN2C
                         BYEBYE
                         GETFOV
                         SINCPT
                         RECLAT
                         ILUMIN
                         ET2LST
 
   Refer to the headers of the various routines listed above, as detailed
   interface specifications are provided with the source code.
 
 
Time Conversion (convtm)
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that prompts the user for an input UTC time string,
   converts it to the following time systems and output formats:
 
       1.   Ephemeris Time (ET) in seconds past J2000
 
       2.   Calendar Ephemeris Time
 
       3.   Spacecraft Clock Time
 
   and displays the results. Use the program to convert "2004 jun 11
   19:32:00" UTC into these alternate systems.
 
 
Learning Goals
--------------------------------------------------------
 
   Familiarity with the various time conversion and parsing routines
   available in the Toolkit. Exposure to source code headers and their
   usage in learning to call routines.
 
 
Approach
--------------------------------------------------------
 
   The solution to the problem can be broken down into a series of simple
   steps:
 
       --   Decide which SPICE kernels are necessary. Prepare a meta-kernel
            listing the kernels and load it into the program.
 
       --   Prompt the user for an input UTC time string.
 
       --   Convert the input time string into ephemeris time expressed as
            seconds past J2000 TDB. Display the result.
 
       --   Convert ephemeris time into a calendar format. Display the
            result.
 
       --   Convert ephemeris time into a spacecraft clock string. Display
            the result.
 
   You may find it useful to consult the permuted index, the headers of
   various source modules, and the ``Time Required Reading'' (time.req) and
   ``SCLK Required Reading'' (sclk.req) documents.
 
   When completing the ``calendar format'' step above, consider using one
   of two possible methods: ETCAL or TIMOUT.
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'convtm.tm'. Its contents follow:
 
      KPL/MK
 
      This is the meta-kernel used in the solution of the ``Time
      Conversion'' task in the Remote Sensing Hands On Lesson.
 
         \begindata
         KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls',
                             'kernels/sclk/cas00084.tsc' )
         \begintext
 
 
 
 
Solution Source Code
 
   A sample solution to the problem follows:
 
            PROGRAM CONVTM
 
            IMPLICIT NONE
 
      C
      C     Local Parameters
      C
      C     The name of the meta-kernel that lists the kernels
      C     to load into the program.
      C
            CHARACTER*(*)         METAKR
            PARAMETER           ( METAKR = 'convtm.tm' )
 
      C
      C     The spacecraft clock ID code for CASSINI.
      C
            INTEGER               SCLKID
            PARAMETER           ( SCLKID = -82 )
 
      C
      C     The length of various string variables.
      C
            INTEGER               STRLEN
            PARAMETER           ( STRLEN = 50 )
 
      C
      C     Local Variables
      C
            CHARACTER*(STRLEN)    CALET
            CHARACTER*(STRLEN)    SCLKST
            CHARACTER*(STRLEN)    UTCTIM
 
            DOUBLE PRECISION      ET
 
      C
      C     Load the kernels this program requires.
      C     Both the spacecraft clock kernel and a
      C     leapseconds kernel should be listed
      C     in the meta-kernel.
      C
            CALL FURNSH ( METAKR )
 
      C
      C     Prompt the user for the input time string.
      C
            CALL PROMPT ( 'Input UTC Time: ', UTCTIM )
 
            WRITE (*,*) 'Converting UTC Time: ', UTCTIM
 
      C
      C     Convert UTCTIM to ET.
      C
            CALL STR2ET ( UTCTIM, ET )
 
            WRITE (*,'(A,F16.3)') '   ET Seconds Past J2000: ', ET
 
      C
      C     Now convert ET to a formal calendar time
      C     string.  This can be accomplished in two
      C     ways.
      C
            CALL ETCAL ( ET, CALET )
 
            WRITE (*,*) '   Calendar ET (ETCAL): ', CALET
 
      C
      C     Or use TIMOUT for finer control over the
      C     output format.  The picture below was built
      C     by examining the header of TIMOUT.
      C
            CALL TIMOUT ( ET, 'YYYY-MON-DDTHR:MN:SC ::TDB', CALET )
 
            WRITE (*,*) '   Calendar ET (TIMOUT): ', CALET
 
      C
      C     Convert ET to spacecraft clock time.
      C
            CALL SCE2S ( SCLKID, ET, SCLKST )
 
            WRITE (*,*) '   Spacecraft Clock Time: ', SCLKST
 
            END
 
 
Solution Sample Output
 
   After compiling the program, execute it:
 
      Converting UTC Time: 2004 jun 11 19:32:00
         ET Seconds Past J2000:    140254384.185
          Calendar ET (ETCAL): 2004 JUN 11 19:33:04.184
          Calendar ET (TIMOUT): 2004-JUN-11T19:33:04
          Spacecraft Clock Time: 1/1465674964.105
 
 
Obtaining Target States and Positions (getsta)
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that prompts the user for an input UTC time string,
   computes the following quantities at that epoch:
 
       1.   The apparent state of Phoebe as seen from CASSINI in the J2000
            frame, in kilometers and kilometers/second. This vector itself
            is not of any particular interest, but it is a useful
            intermediate quantity in some geometry calculations.
 
       2.   The apparent position of the Earth as seen from CASSINI in the
            J2000 frame, in kilometers.
 
       3.   The one-way light time between CASSINI and the apparent
            position of Earth, in seconds.
 
       4.   The apparent position of the Sun as seen from Phoebe in the
            J2000 frame (J2000), in kilometers.
 
       5.   The actual (geometric) distance between the Sun and Phoebe, in
            astronomical units.
 
   and displays the results. Use the program to compute these quantities at
   "2004 jun 11 19:32:00" UTC.
 
 
Learning Goals
--------------------------------------------------------
 
   Understand the anatomy of an SPKEZR call. Discover the difference
   between SPKEZR and SPKPOS. Familiarity with the Toolkit utility
   ``brief''. Exposure to unit conversion with SPICE.
 
 
Approach
--------------------------------------------------------
 
   The solution to the problem can be broken down into a series of simple
   steps:
 
       --   Decide which SPICE kernels are necessary. Prepare a meta-kernel
            listing the kernels and load it into the program.
 
       --   Prompt the user for an input time string.
 
       --   Convert the input time string into ephemeris time expressed as
            seconds past J2000 TDB.
 
       --   Compute the state of Phoebe relative to CASSINI in the J2000
            reference frame, corrected for aberrations.
 
       --   Compute the position of Earth relative to CASSINI in the J2000
            reference frame, corrected for aberrations. (The routine in the
            library that computes this also returns the one-way light time
            between CASSINI and Earth.)
 
       --   Compute the position of the Sun relative to Phoebe in the J2000
            reference frame, corrected for aberrations.
 
       --   Compute the position of the Sun relative to Phoebe without
            correcting for aberration.
 
       --   Compute the length of this vector. This provides the desired
            distance in kilometers.
 
       --   Convert the distance in kilometers into AU.
 
   You may find it useful to consult the permuted index, the headers of
   various source modules, and the ``SPK Required Reading'' (spk.req)
   document.
 
   When deciding which SPK files to load, the Toolkit utility ``brief'' may
   be of some use.
 
   ``brief'' is located in the ``toolkit/exe'' directory for FORTRAN
   toolkits. Consult its user's guide available in ``toolkit/doc/brief.ug''
   for details.
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'getsta.tm'. Its contents follow:
 
      KPL/MK
 
      This is the meta-kernel used in the solution of the
      ``Obtaining Target States and Positions'' task in the
      Remote Sensing Hands On Lesson.
 
         \begindata
         KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls',
                             'kernels/spk/981005_PLTEPH-DE405S.bsp',
                             'kernels/spk/020514_SE_SAT105.bsp',
                             'kernels/spk/030201AP_SK_SM546_T45.bsp' )
         \begintext
 
 
Solution Source Code
 
   A sample solution to the problem follows:
 
            PROGRAM GETSTA
 
            IMPLICIT NONE
 
      C
      C     SPICELIB Functions
      C
            DOUBLE PRECISION      VNORM
 
      C
      C     Local Parameters
      C
      C
      C     The name of the meta-kernel that lists the kernels
      C     to load into the program.
      C
            CHARACTER*(*)         METAKR
            PARAMETER           ( METAKR = 'getsta.tm' )
 
      C
      C     The length of various string variables.
      C
            INTEGER               STRLEN
            PARAMETER           ( STRLEN = 50 )
 
      C
      C     Local Variables
      C
            CHARACTER*(STRLEN)    UTCTIM
 
            DOUBLE PRECISION      DIST
            DOUBLE PRECISION      ET
            DOUBLE PRECISION      LTIME
            DOUBLE PRECISION      POS   ( 3 )
            DOUBLE PRECISION      STATE ( 6 )
 
      C
      C     Load the kernels that this program requires.  We
      C     will need a leapseconds kernel to convert input
      C     UTC time strings into ET.  We also will need the
      C     necessary SPK files with coverage for the bodies
      C     in which we are interested.
      C
            CALL FURNSH ( METAKR )
 
      C
      C     Prompt the user for the input time string.
      C
            CALL PROMPT ( 'Input UTC Time: ', UTCTIM )
 
            WRITE (*,*) 'Converting UTC Time: ', UTCTIM
 
      C
      C     Convert UTCTIM to ET.
      C
            CALL STR2ET ( UTCTIM, ET )
 
            WRITE (*,'(A,F16.3)') '   ET seconds past J2000: ', ET
 
      C
      C     Compute the apparent state of Phoebe as seen from
      C     CASSINI in the J2000 frame.  All of the ephemeris
      C     readers return states in units of kilometers and
      C     kilometers per second.
      C
            CALL SPKEZR ( 'PHOEBE', ET,    'J2000', 'LT+S',
           .              'CASSINI',  STATE, LTIME               )
 
            WRITE (*,*) '   Apparent state of Phoebe as seen from '
           .//          'CASSINI in the J2000'
            WRITE (*,*) '      frame (km, km/s):'
 
            WRITE (*,'(A,F16.3)') '      X = ', STATE(1)
            WRITE (*,'(A,F16.3)') '      Y = ', STATE(2)
            WRITE (*,'(A,F16.3)') '      Z = ', STATE(3)
            WRITE (*,'(A,F16.3)') '     VX = ', STATE(4)
            WRITE (*,'(A,F16.3)') '     VY = ', STATE(5)
            WRITE (*,'(A,F16.3)') '     VZ = ', STATE(6)
 
      C
      C     Compute the apparent position of Earth as seen from
      C     CASSINI in the J2000 frame.  Note: We could have continued
      C     using SPKEZR and simply ignored the velocity components.
      C
            CALL SPKPOS ( 'EARTH', ET,  'J2000', 'LT+S',
           .              'CASSINI',   POS, LTIME               )
 
            WRITE (*,*) '   Apparent position of Earth as seen from '
           .//          'CASSINI in the J2000'
            WRITE (*,*) '      frame (km):'
 
            WRITE (*,'(A,F16.3)') '      X = ', POS(1)
            WRITE (*,'(A,F16.3)') '      Y = ', POS(2)
            WRITE (*,'(A,F16.3)') '      Z = ', POS(3)
 
      C
      C     We need only display LTIME, as it is precisely the light
      C     time in which we are interested.
      C
            WRITE (*,*) '   One way light time between CASSINI and the '
           .//          'apparent position'
            WRITE (*,'(A,F16.3)') '      of Earth (seconds): ', LTIME
 
      C
      C     Compute the apparent position of the Sun as seen from
      C     Phoebe in the J2000 frame.
      C
            CALL SPKPOS ( 'SUN',  ET,  'J2000', 'LT+S',
           .              'PHOEBE', POS, LTIME                    )
 
            WRITE (*,*) '   Apparent position of Sun as seen from '
           .//          'Phoebe in the'
            WRITE (*,*) '      J2000 frame (km):'
 
            WRITE (*,'(A,F16.3)') '      X = ', POS(1)
            WRITE (*,'(A,F16.3)') '      Y = ', POS(2)
            WRITE (*,'(A,F16.3)') '      Z = ', POS(3)
 
      C
      C     Now we need to compute the actual distance between the Sun
      C     and Phoebe.  The above SPKPOS call gives us the apparent
      C     distance, so we need to adjust our aberration correction
      C     appropriately.
      C
            CALL SPKPOS ( 'SUN',  ET,  'J2000', 'NONE',
           .              'PHOEBE', POS, LTIME                  )
 
      C
      C     Compute the distance between the body centers in
      C     kilometers.
      C
            DIST = VNORM(POS)
 
      C
      C     Convert this value to AU using CONVRT.
      C
            CALL CONVRT ( DIST, 'KM', 'AU', DIST )
 
            WRITE (*,*) '   Actual distance between Sun and Phoebe body '
           .//          'centers: '
            WRITE (*,'(A,F16.3)') '      (AU):', DIST
 
            END
 
 
Solution Sample Output
 
   After compiling the program, execute it:
 
      Converting UTC Time: 2004 JUN 11 19:32:00
         ET seconds past J2000:    140254384.185
          Apparent state of Phoebe as seen from CASSINI in the J2000
             frame (km, km/s):
            X =         -119.921
            Y =         2194.139
            Z =          -57.639
           VX =           -5.980
           VY =           -2.119
           VZ =           -0.295
          Apparent position of Earth as seen from CASSINI in the J2000
             frame (km):
            X =    353019393.123
            Y =  -1328180352.140
            Z =   -568134171.697
          One way light time between CASSINI and the apparent position
            of Earth (seconds):         4960.427
          Apparent position of Sun as seen from Phoebe in the
             J2000 frame (km):
            X =    376551465.272
            Y =  -1190495630.303
            Z =   -508438699.110
          Actual distance between Sun and Phoebe body centers:
            (AU):           9.012
 
 
Spacecraft Orientation and Reference Frames (xform)
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that prompts the user for an input time string, computes
   and displays the following at the epoch of interest:
 
       1.   The apparent state of Phoebe as seen from CASSINI in the
            IAU_PHOEBE body-fixed frame. This vector itself is not of any
            particular interest, but it is a useful intermediate quantity
            in some geometry calculations.
 
       2.   The angular separation between the apparent position of Earth
            as seen from CASSINI and the nominal boresight of the CASSINI
            high gain antenna (HGA).
 
            The HGA boresight direction is provided by the kernel variable
            TKFRAME_-82101_BORESIGHT, which is defined in the Cassini frame
            kernel cited above in the section ``Kernels Used.'' In this
            kernel, the HGA boresight vector is expressed relative to the
            CASSINI_HGA reference frame.
 
   Use the program to compute these quantities at the epoch "2004 jun 11
   19:32:00" UTC.
 
 
Learning Goals
--------------------------------------------------------
 
   Familiarity with the different types of kernels involved in chaining
   reference frames together, both inertial and non-inertial. Discover some
   of the matrix and vector math routines. Understand the difference
   between PXFORM and SXFORM.
 
 
Approach
--------------------------------------------------------
 
   The solution to the problem can be broken down into a series of simple
   steps:
 
       --   Decide which SPICE kernels are necessary. Prepare a meta-kernel
            listing the kernels and load it into the program.
 
       --   Prompt the user for an input time string.
 
       --   Convert the input time string into ephemeris time expressed as
            seconds past J2000 TDB.
 
       --   Compute the state of Phoebe relative to CASSINI in the J2000
            reference frame, corrected for aberrations.
 
       --   Compute the state transformation matrix from J2000 to
            IAU_PHOEBE at the epoch, adjusted for light time.
 
       --   Multiply the state of Phoebe relative to CASSINI in the J2000
            reference frame by the state transformation matrix computed in
            the previous step.
 
       --   Compute the position of Earth relative to CASSINI in the J2000
            reference frame, corrected for aberrations.
 
       --   Determine what the nominal boresight of the CASSINI high gain
            antenna is by examining the frame kernel's content.
 
       --   Compute the rotation matrix from the CASSINI high gain antenna
            frame to J2000.
 
       --   Multiply the nominal boresight expressed in the CASSINI high
            gain antenna frame by the rotation matrix from the previous
            step.
 
       --   Compute the separation between the result of the previous step
            and the apparent position of the Earth relative to CASSINI in
            the J2000 frame.
 
   HINT: Several of the steps above may be compressed into a single using
   SPICE routines with which you are already familiar. The ``long-way''
   presented above is intended to facilitate the introduction of the
   routines PXFORM and SXFORM.
 
   You may find it useful to consult the permuted index, the headers of
   various source modules, and the following toolkit documentation:
 
       1.   Frames Required Reading (frames.req)
 
       2.   PCK Required Reading (pck.req)
 
       3.   SPK Required Reading (spk.req)
 
       4.   CK Required Reading (ck.req)
 
   This particular example makes use of many of the different types of
   SPICE kernels. You should spend a few moments thinking about which
   kernels you will need and what data they provide.
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'xform.tm'. Its contents follow:
 
      KPL/MK
 
      This is the meta-kernel used in the solution of the ``Spacecraft
      Orientation and Reference Frames'' task in the Remote Sensing
      Hands On Lesson.
 
         \begindata
         KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls',
                             'kernels/sclk/cas00084.tsc',
                             'kernels/spk/981005_PLTEPH-DE405S.bsp',
                             'kernels/spk/020514_SE_SAT105.bsp',
                             'kernels/spk/030201AP_SK_SM546_T45.bsp',
                             'kernels/fk/cas_v37.tf',
                             'kernels/ck/04135_04171pc_psiv2.bc',
                             'kernels/pck/cpck05Mar2004.tpc' )
         \begintext
 
 
Solution Source Code
 
   A sample solution to the problem follows:
 
            PROGRAM XFORM
 
            IMPLICIT NONE
 
      C
      C     SPICELIB Functions
      C
            DOUBLE PRECISION      VSEP
 
      C
      C     Local Parameters
      C
      C
      C     The name of the meta-kernel that lists the kernels
      C     to load into the program.
      C
            CHARACTER*(*)         METAKR
            PARAMETER           ( METAKR = 'xform.tm' )
 
      C
      C     The length of various string variables.
      C
            INTEGER               STRLEN
            PARAMETER           ( STRLEN = 50 )
 
      C
      C     Local Variables
      C
            CHARACTER*(STRLEN)    UTCTIM
 
            DOUBLE PRECISION      ET
            DOUBLE PRECISION      LTIME
            DOUBLE PRECISION      STATE  ( 6 )
            DOUBLE PRECISION      BFIXST ( 6 )
            DOUBLE PRECISION      POS    ( 3 )
            DOUBLE PRECISION      SXFMAT ( 6, 6 )
            DOUBLE PRECISION      PFORM  ( 3, 3 )
            DOUBLE PRECISION      BSIGHT ( 3 )
            DOUBLE PRECISION      SEP
 
      C
      C     Load the kernels that this program requires.  We
      C     will need:
      C
      C        A leapseconds kernel
      C        A spacecraft clock kernel for CASSINI
      C        The necessary ephemerides
      C        A planetary constants file (PCK)
      C        A spacecraft orientation kernel for CASSINI (CK)
      C        A frame kernel (TF)
      C
            CALL FURNSH ( METAKR )
 
      C
      C     Prompt the user for the input time string.
      C
            CALL PROMPT ( 'Input UTC Time: ', UTCTIM )
 
            WRITE (*,*) 'Converting UTC Time: ', UTCTIM
 
      C
      C     Convert UTCTIM to ET.
      C
            CALL STR2ET ( UTCTIM, ET )
 
            WRITE (*,'(A,F16.3)') '   ET seconds past J2000: ', ET
 
      C
      C     Compute the apparent state of Phoebe as seen from CASSINI
      C     in the J2000 reference frame.
      C
            CALL SPKEZR ( 'PHOEBE',   ET,    'J2000', 'LT+S',
           .              'CASSINI',  STATE, LTIME           )
 
      C
      C     Now obtain the transformation from the inertial
      C     J2000 frame to the non-inertial, body-fixed IAU_PHOEBE
      C     frame. Since we'll use this transformation to produce
      C     the apparent state in the IAU_PHOEBE reference frame,
      C     we need to correct the orientation of this frame for
      C     one-way light time; hence we subtract LTIME from ET
      C     in the call below.
      C
            CALL SXFORM ( 'J2000', 'IAU_PHOEBE', ET-LTIME, SXFMAT )
 
      C
      C     Now transform the apparent J2000 state into IAU_PHOEBE
      C     with the following matrix multiplication:
      C
            CALL MXVG ( SXFMAT, STATE, 6, 6, BFIXST )
 
      C
      C     Display the results.
      C
            WRITE (*,*) '   Apparent state of Phoebe as seen from '
           .//          'CASSINI in the IAU_PHOEBE'
            WRITE (*,*) '      body-fixed frame (km, km/s):'
            WRITE (*,'(A,F19.6)') '      X = ', BFIXST(1)
            WRITE (*,'(A,F19.6)') '      Y = ', BFIXST(2)
            WRITE (*,'(A,F19.6)') '      Z = ', BFIXST(3)
            WRITE (*,'(A,F19.6)') '     VX = ', BFIXST(4)
            WRITE (*,'(A,F19.6)') '     VY = ', BFIXST(5)
            WRITE (*,'(A,F19.6)') '     VZ = ', BFIXST(6)
 
      C
      C     It is worth pointing out, all of the above could have
      C     been done with a single call to SPKEZR:
      C
            CALL SPKEZR ( 'PHOEBE', ET,    'IAU_PHOEBE', 'LT+S',
           .              'CASSINI',  STATE, LTIME               )
 
      C
      C     Display the results.
      C
            WRITE (*,*) '   Apparent state of Phoebe as seen from CASSINI '
           .//          'in the IAU_PHOEBE'
            WRITE (*,*) '      body-fixed frame (km, km/s) '
           .//          'obtained using SPKEZR directly:'
            WRITE (*,'(A,F19.6)') '      X = ', STATE(1)
            WRITE (*,'(A,F19.6)') '      Y = ', STATE(2)
            WRITE (*,'(A,F19.6)') '      Z = ', STATE(3)
            WRITE (*,'(A,F19.6)') '     VX = ', STATE(4)
            WRITE (*,'(A,F19.6)') '     VY = ', STATE(5)
            WRITE (*,'(A,F19.6)') '     VZ = ', STATE(6)
 
      C
      C     Note that the velocity found by using SPKEZR
      C     to compute the state in the IAU_PHOEBE frame differs
      C     at the few mm/second level from that found previously
      C     by calling SPKEZR and then SXFORM. Computing velocity
      C     via a single call to SPKEZR as we've done immediately
      C     above is slightly more accurate because it accounts for
      C     the effect of the rate of change of light time on the
      C     apparent angular velocity of the target's body-fixed
      C     reference frame.
      C
      C     Now we are to compute the angular separation between
      C     the apparent position of the Earth as seen from the
      C     orbiter and the nominal boresight of the high gain
      C     antenna.  First, compute the apparent position of
      C     the Earth as seen from CASSINI in the J2000 frame.
      C
            CALL SPKPOS ( 'EARTH', ET,  'J2000', 'LT+S',
           .              'CASSINI',   POS, LTIME               )
 
      C
      C     Now compute the location of the antenna boresight
      C     at this same epoch.  From reading the frame kernel
      C     we know that the antenna boresight is nominally the
      C     +Z axis of the CASSINI_HGA frame defined there.
      C
            BSIGHT(1) = 0.0D0
            BSIGHT(2) = 0.0D0
            BSIGHT(3) = 1.0D0
 
      C
      C     Now compute the rotation matrix from CASSINI_HGA into
      C     J2000.
      C
            CALL PXFORM ( 'CASSINI_HGA', 'J2000', ET, PFORM )
 
      C
      C     And multiply the result to obtain the nominal antenna
      C     boresight in the J2000 reference frame.
      C
            CALL MXV ( PFORM, BSIGHT, BSIGHT )
 
      C
      C     Lastly compute the angular separation.
      C
            CALL CONVRT ( VSEP(BSIGHT, POS), 'RADIANS',
           .              'DEGREES',         SEP        )
 
            WRITE (*,*) '   Angular separation between the '
           .//          'apparent position of'
            WRITE (*,*) '      Earth and the CASSINI high '
           .//          'gain antenna boresight (degrees): '
            WRITE (*,'(A,F19.3)') '      ', SEP
 
      C
      C     Or, alternately we can work in the antenna
      C     frame directly.
      C
            CALL SPKPOS ( 'EARTH', ET,  'CASSINI_HGA', 'LT+S',
           .              'CASSINI',   POS, LTIME              )
 
      C
      C     The antenna boresight is the Z-axis in the
      C     CASSINI_HGA frame.
      C
            BSIGHT(1) = 0.0D0
            BSIGHT(2) = 0.0D0
            BSIGHT(3) = 1.0D0
 
      C
      C     Lastly compute the angular separation.
      C
            CALL CONVRT ( VSEP(BSIGHT, POS), 'RADIANS',
           .              'DEGREES',         SEP        )
 
            WRITE (*,*) '   Angular separation between the '
           .//          'apparent position of'
            WRITE (*,*) '      Earth and the CASSINI high gain '
           .//          'antenna boresight computed '
            WRITE (*,*) '      using vectors in the CASSINI_HGA '
           .//          'frame (degrees): '
            WRITE (*,'(A,F19.3)') '      ', SEP
 
            END
 
 
Solution Sample Output
 
   After compiling the program, execute it:
 
      Input UTC Time:  Converting UTC Time: 2004 JUN 11 19:32:00
         ET seconds past J2000:    140254384.185
          Apparent state of Phoebe as seen from CASSINI in the IAU_PHOEBE
             body-fixed frame (km, km/s):
            X =        -1982.639762
            Y =         -934.530471
            Z =         -166.562595
           VX =            3.970833
           VY =           -3.812498
           VZ =           -2.371663
          Apparent state of Phoebe as seen from CASSINI in the IAU_PHOEBE
             body-fixed frame (km, km/s) obtained using SPKEZR directly:
            X =        -1982.639762
            Y =         -934.530471
            Z =         -166.562595
           VX =            3.970832
           VY =           -3.812496
           VZ =           -2.371663
          Angular separation between the apparent position of
             Earth and the CASSINI high gain antenna boresight (degrees):
                         71.924
          Angular separation between the apparent position of
             Earth and the CASSINI high gain antenna boresight computed
             using vectors in the CASSINI_HGA frame (degrees):
                         71.924
 
 
Computing Sub-spacecraft and Sub-solar Points (subpts)
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that prompts the user for an input UTC time string,
   computes the following quantities at that epoch:
 
       1.   The apparent sub-observer point of CASSINI on Phoebe in the
            body fixed frame IAU_PHOEBE in kilometers.
 
       2.   The apparent sub-solar point on Phoebe as seen from CASSINI in
            the body fixed frame IAU_PHOEBE in kilometers.
 
   and displays the results. Use the program to compute these quantities at
   "2004 jun 11 19:32:00" UTC.
 
 
Learning Goals
--------------------------------------------------------
 
   Discover higher level geometry calculation routines in SPICE and their
   usage as it relates to CASSINI.
 
 
Approach
--------------------------------------------------------
 
   This particular problem is more of an exercise in searching the permuted
   index to find the appropriate routines and then reading their headers to
   understand how to call them.
 
   One point worth considering: Which method do you want to use to compute
   the sub-solar (or sub-observer) point?
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'subpts.tm'. Its contents follow:
 
      KPL/MK
 
      This is the meta-kernel used in the solution of the
      ``Computing Sub-spacecraft and Sub-solar Points'' task
      in the Remote Sensing Hands On Lesson.
 
         \begindata
         KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls',
                             'kernels/spk/981005_PLTEPH-DE405S.bsp',
                             'kernels/spk/020514_SE_SAT105.bsp',
                             'kernels/spk/030201AP_SK_SM546_T45.bsp',
                             'kernels/pck/cpck05Mar2004.tpc' )
         \begintext
 
 
Solution Source Code
 
   A sample solution to the problem follows:
 
            PROGRAM SUBPTS
 
            IMPLICIT NONE
      C
      C     SPICELIB functions
      C
            DOUBLE PRECISION      VNORM
 
      C
      C     Local Parameters
      C
      C
      C     The name of the meta-kernel that lists the kernels
      C     to load into the program.
      C
            CHARACTER*(*)         METAKR
            PARAMETER           ( METAKR = 'subpts.tm' )
 
      C
      C     The length of various string variables.
      C
            INTEGER               STRLEN
            PARAMETER           ( STRLEN = 50 )
 
      C
      C     Local Variables
      C
            CHARACTER*(STRLEN)    UTCTIM
 
            DOUBLE PRECISION      ET
            DOUBLE PRECISION      SPOINT ( 3 )
            DOUBLE PRECISION      SRFVEC ( 3 )
            DOUBLE PRECISION      TRGEPC
 
      C
      C     Load the kernels that this program requires.  We
      C     will need:
      C
      C        A leapseconds kernel
      C        The necessary ephemerides
      C        A planetary constants file (PCK)
      C
            CALL FURNSH ( METAKR )
 
      C
      C     Prompt the user for the input time string.
      C
            CALL PROMPT ( 'Input UTC Time: ', UTCTIM )
 
            WRITE (*,*) 'Converting UTC Time: ', UTCTIM
 
      C
      C     Convert UTCTIM to ET.
      C
            CALL STR2ET ( UTCTIM, ET )
 
            WRITE (*,'(A,F16.3)') '   ET seconds past J2000: ', ET
 
      C
      C     Compute the apparent sub-observer point of CASSINI on Phoebe.
      C
            CALL SUBPNT ( 'NEAR POINT: ELLIPSOID',
           .              'PHOEBE',  ET,     'IAU_PHOEBE', 'LT+S',
           .              'CASSINI', SPOINT, TRGEPC,       SRFVEC )
 
            WRITE (*,*) '   Apparent sub-observer point of CASSINI '
           .//          'on Phoebe in the'
            WRITE (*,*) '   IAU_PHOEBE frame (km):'
            WRITE (*,'(A,F16.3)') '      X = ', SPOINT(1)
            WRITE (*,'(A,F16.3)') '      Y = ', SPOINT(2)
            WRITE (*,'(A,F16.3)') '      Z = ', SPOINT(3)
            WRITE (*,'(A,F16.3)') '    ALT = ', VNORM(SRFVEC)
 
      C
      C     Compute the apparent sub-solar point on Phoebe as seen
      C     from CASSINI.
      C
            CALL SUBSLR ( 'NEAR POINT: ELLIPSOID',
           .              'PHOEBE',  ET,     'IAU_PHOEBE', 'LT+S',
           .              'CASSINI', SPOINT, TRGEPC,       SRFVEC )
 
            WRITE (*,*) '   Apparent sub-solar point on Phoebe as '
           .//          'seen from CASSINI in'
            WRITE (*,*) '   the IAU_PHOEBE frame (km):'
            WRITE (*,'(A,F16.3)') '      X = ', SPOINT(1)
            WRITE (*,'(A,F16.3)') '      Y = ', SPOINT(2)
            WRITE (*,'(A,F16.3)') '      Z = ', SPOINT(3)
 
            END
 
 
Solution Sample Output
 
   After compiling the program, execute it:
 
      Converting UTC Time: 2004 JUN 11 19:32:00
         ET seconds past J2000:    140254384.185
          Apparent sub-observer point of CASSINI on Phoebe in the
          IAU_PHOEBE frame (km):
            X =          104.498
            Y =           45.269
            Z =            7.383
          ALT =         2084.116
          Apparent sub-solar point on Phoebe as seen from CASSINI in
          the IAU_PHOEBE frame (km):
            X =           78.681
            Y =           76.879
            Z =          -21.885
 
 
Intersecting Vectors with a Triaxial Ellipsoid (fovint)
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that prompts the user for an input UTC time string and,
   for that time, computes the intersection of the CASSINI ISS NAC camera
   boresight and field of view (FOV) boundary vectors with the surface of
   Phoebe. The program presents each point of intersection as
 
       1.   A cartesian vector in the IAU_PHOEBE frame
 
       2.   Planetocentric (latitudinal) coordinates in the IAU_PHOEBE
            frame.
 
   For each vector, if an intersection is found, the program displays the
   results of the above computations, otherwise it indicates no
   intersection has occurred.
 
   At each point of intersection compute the following:
 
       3.   Phase angle
 
       4.   Solar incidence angle
 
       5.   Emission angle
 
   Additionally compute the local solar time at the intercept of the camera
   boresight with the surface of Phoebe.
 
   Use this program to compute values at the epoch:
 
            2004 jun 11 19:32:00 UTC
 
 
Learning Goals
--------------------------------------------------------
 
   Understand how field of view parameters are retrieved from instrument
   kernels. Learn how various standard planetary constants are retrieved
   from text PCKs. Discover how to compute the intersection of field of
   view vectors with triaxial ellipsoidal target bodies. Discover another
   high level geometry routine and another time conversion routine in
   SPICE.
 
 
Approach
--------------------------------------------------------
 
   This problem can be broken down into several simple, small steps:
 
       --   Decide which SPICE kernels are necessary. Prepare a meta-kernel
            listing the kernels and load it into the program. Remember, you
            will need to find a kernel with information about the CASSINI
            NAC camera.
 
       --   Prompt the user for an input time string.
 
       --   Convert the input time string into ephemeris time expressed as
            seconds past J2000 TDB.
 
       --   Retrieve the FOV (field of view) configuration for the CASSINI
            NAC camera.
 
   For each vector in the set of boundary corner vectors, and for the
   boresight vector, perform the following operations:
 
       --   Compute the intercept of the vector with Phoebe.
 
       --   If this intercept is found, convert the position vector of the
            intercept into planetocentric coordinates.
 
            Then compute the phase, solar incidence, and emission angles at
            the intercept. Otherwise indicate to the user no intercept was
            found for this vector.
 
       --   Compute the planetocentric longitude of the boresight
            intercept.
 
   Finally
 
       --   Compute the local solar time at the boresight intercept
            longitude on a 24-hour clock. The input time for this
            computation should be the TDB observation epoch minus one-way
            light time from the boresight intercept to the spacecraft.
 
   It may be useful to consult the CASSINI ISS instrument kernel to
   determine the name of the NAC camera as well as its configuration. This
   exercise may make use of some of the concepts and (loosely) code from
   the ``Spacecraft Orientation and Reference Frames'' task.
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'fovint.tm'. Its contents follow:
 
      KPL/MK
 
      This is the meta-kernel used in the solution of the
      ``Intersecting Vectors with a Triaxial Ellipsoid'' task
      in the Remote Sensing Hands On Lesson.
 
         \begindata
         KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls',
                             'kernels/sclk/cas00084.tsc',
                             'kernels/spk/981005_PLTEPH-DE405S.bsp',
                             'kernels/spk/020514_SE_SAT105.bsp',
                             'kernels/spk/030201AP_SK_SM546_T45.bsp',
                             'kernels/fk/cas_v37.tf',
                             'kernels/ck/04135_04171pc_psiv2.bc',
                             'kernels/pck/cpck05Mar2004.tpc',
                             'kernels/ik/cas_iss_v09.ti' )
         \begintext
 
 
Solution Source Code
 
   A sample solution to the problem follows:
 
            PROGRAM FOVINT
 
            IMPLICIT NONE
 
      C
      C     SPICELIB functions
      C
            DOUBLE PRECISION      DPR
 
      C
      C     Local Parameters
      C
      C
      C     The name of the meta-kernel that lists the kernels
      C     to load into the program.
      C
            CHARACTER*(*)         METAKR
            PARAMETER           ( METAKR = 'fovint.tm' )
 
      C
      C     The length of various string variables.
      C
            INTEGER               STRLEN
            PARAMETER           ( STRLEN = 50 )
 
      C
      C     The maximum number of boundary corner vectors
      C     we can retrieve.
      C
            INTEGER               BCVLEN
            PARAMETER           ( BCVLEN = 5 )
 
      C
      C     Local Variables
      C
            CHARACTER*(STRLEN)    AMPM
            CHARACTER*(STRLEN)    INSFRM
            CHARACTER*(STRLEN)    SHAPE
            CHARACTER*(STRLEN)    TIME
            CHARACTER*(STRLEN)    UTCTIM
            CHARACTER*(STRLEN)    VECNAM ( BCVLEN )
 
            DOUBLE PRECISION      BOUNDS ( 3, BCVLEN )
            DOUBLE PRECISION      BSIGHT ( 3 )
            DOUBLE PRECISION      EMISSN
            DOUBLE PRECISION      ET
            DOUBLE PRECISION      LAT
            DOUBLE PRECISION      LON
            DOUBLE PRECISION      PHASE
            DOUBLE PRECISION      POINT  ( 3 )
            DOUBLE PRECISION      RADIUS
            DOUBLE PRECISION      SOLAR
            DOUBLE PRECISION      SRFVEC ( 3 )
            DOUBLE PRECISION      TRGEPC
 
            INTEGER               HR
            INTEGER               I
            INTEGER               MN
            INTEGER               N
            INTEGER               NACID
            INTEGER               PHOEID
            INTEGER               SC
 
            LOGICAL               FOUND
 
      C
      C     Load the kernels that this program requires. We
      C     will need:
      C
      C        A leapseconds kernel.
      C        A SCLK kernel for CASSINI.
      C        Any necessary ephemerides.
      C        The CASSINI frame kernel.
      C        A CASSINI C-kernel.
      C        A PCK file with Phoebe constants.
      C        The CASSINI ISS I-kernel.
      C
            CALL FURNSH ( METAKR )
 
      C
      C     Prompt the user for the input time string.
      C
            CALL PROMPT ( 'Input UTC Time: ', UTCTIM )
 
            WRITE (*,*) 'Converting UTC Time: ', UTCTIM
 
      C
      C     Convert UTCTIM to ET.
      C
            CALL STR2ET ( UTCTIM, ET )
 
            WRITE (*,'(A,F16.3)') '   ET seconds past J2000: ', ET
 
      C
      C     Now we need to obtain the FOV configuration of the NAC
      C     camera. To do this we will need the ID code for
      C     CASSINI_ISS_NAC.
      C
            CALL BODN2C ( 'CASSINI_ISS_NAC', NACID, FOUND )
 
      C
      C     Stop the program if the code was not found.
      C
            IF ( .NOT. FOUND ) THEN
               WRITE (*,*) 'Unable to locate the ID code for '
           .   //          'CASSINI_ISS_NAC'
               CALL BYEBYE ( 'FAILURE' )
            END IF
 
      C
      C     Now retrieve the field of view parameters.
      C
            CALL GETFOV ( NACID,  BCVLEN, SHAPE, INSFRM,
           .              BSIGHT, N,      BOUNDS        )
 
      C
      C     Rather than treat BSIGHT as a separate vector,
      C     copy it into the last slot of BOUNDS.
      C
            CALL MOVED ( BSIGHT, 3, BOUNDS(1,5) )
 
      C
      C     Define names for each of the vectors for display
      C     purposes.
      C
            VECNAM (1) = 'Boundary Corner 1'
            VECNAM (2) = 'Boundary Corner 2'
            VECNAM (3) = 'Boundary Corner 3'
            VECNAM (4) = 'Boundary Corner 4'
            VECNAM (5) = 'Cassini NAC Boresight'
 
      C
      C     Now perform the same set of calculations for each
      C     vector listed in the BOUNDS array.
      C
            DO I = 1, 5
      C
      C        Call SINCPT to determine coordinates of the
      C        intersection of this vector with the surface
      C        of Phoebe.
      C
               CALL SINCPT ( 'Ellipsoid',  'PHOEBE',    ET,
           .                 'IAU_PHOEBE', 'LT+S',      'CASSINI',
           .                 INSFRM,       BOUNDS(1,I), POINT,
           .                 TRGEPC,       SRFVEC,      FOUND    )
      C
      C        Check the found flag. Display a message if the point
      C        of intersection was not found, otherwise continue with
      C        the calculations.
      C
               WRITE (*,*) 'Vector: ', VECNAM(I)
 
               IF ( .NOT. FOUND ) THEN
 
                  WRITE (*,*) 'No intersection point found at '
           .      //          'this epoch for this vector.'
 
               ELSE
      C
      C           Now, we have discovered a point of intersection.
      C           Start by displaying the position vector in the
      C           IAU_PHOEBE frame of the intersection.
      C
                  WRITE (*,*) '  Position vector of '
           .      //          'surface intercept in '
           .      //          'the IAU_PHOEBE frame (km):'
                  WRITE (*,'(A,F16.3)') '      X   = ', POINT(1)
                  WRITE (*,'(A,F16.3)') '      Y   = ', POINT(2)
                  WRITE (*,'(A,F16.3)') '      Z   = ', POINT(3)
      C
      C           Display the planetocentric latitude and longitude
      C           of the intercept.
      C
                  CALL RECLAT ( POINT, RADIUS, LON, LAT )
 
                  WRITE (*,*) '  Planetocentric coordinates of the '
           .      //          'intercept (degrees):'
                  WRITE (*,'(A,F16.3)') '      LAT = ', LAT * DPR()
                  WRITE (*,'(A,F16.3)') '      LON = ', LON * DPR()
      C
      C           Compute the illumination angles at this
      C           point.
      C
                  CALL ILUMIN ( 'Ellipsoid',  'PHOEBE',  ET,
           .                    'IAU_PHOEBE', 'LT+S',    'CASSINI',
           .                    POINT,        TRGEPC,    SRFVEC,
           .                    PHASE,        SOLAR,     EMISSN    )
 
                  WRITE (*,'(A,F16.3)') '   Phase angle (degrees):'
           .      //                    '           ', PHASE * DPR()
                  WRITE (*,'(A,F16.3)') '   Solar incidence angle '
           .      //                    '(degrees): ', SOLAR * DPR()
                  WRITE (*,'(A,F16.3)') '   Emission angle (degree'
           .      //                    's):        ', EMISSN* DPR()
 
               END IF
 
               WRITE (*,*) ' '
 
            END DO
 
      C
      C     Lastly compute the local solar time at the boresight
      C     intersection.
      C
            IF ( FOUND ) THEN
      C
      C        Get Phoebe ID.
      C
               CALL BODN2C ( 'PHOEBE', PHOEID, FOUND )
      C
      C        Stop the program if the code was not found.
      C
               IF ( .NOT. FOUND ) THEN
                  WRITE (*,*) 'Unable to locate the ID code for '
           .   //             'PHOEBE'
                  CALL BYEBYE ( 'FAILURE' )
               END IF
      C
      C        Compute local time corresponding to the TDB light time
      C        corrected epoch at the intercept.
      C
               CALL ET2LST ( TRGEPC,
           .                 PHOEID,
           .                 LON,
           .                 'PLANETOCENTRIC',
           .                 HR,
           .                 MN,
           .                 SC,
           .                 TIME,
           .                 AMPM              )
 
               WRITE (*,*) '  Local Solar Time at boresight '
           .   //          'intercept (24 Hour Clock): '
               WRITE (*,*) '     ', TIME
 
            ELSE
 
               WRITE (*,*) '   No boresight intercept to compute '
           .   //          'local solar time.'
 
            END IF
 
            END
 
 
Solution Sample Output
 
   After compiling the program, execute it:
 
      Converting UTC Time: 2004 JUN 11 19:32:00
         ET seconds past J2000:    140254384.185
       Vector: Boundary Corner 1
         Position vector of surface intercept in the IAU_PHOEBE frame (km):
            X   =           91.026
            Y   =           67.190
            Z   =            2.030
         Planetocentric coordinates of the intercept (degrees):
            LAT =            1.028
            LON =           36.433
         Phase angle (degrees):                     28.110
         Solar incidence angle (degrees):           16.121
         Emission angle (degrees):                  14.627
 
       Vector: Boundary Corner 2
         Position vector of surface intercept in the IAU_PHOEBE frame (km):
            X   =           89.991
            Y   =           66.726
            Z   =           14.733
         Planetocentric coordinates of the intercept (degrees):
            LAT =            7.492
            LON =           36.556
         Phase angle (degrees):                     27.894
         Solar incidence angle (degrees):           22.894
         Emission angle (degrees):                  14.988
 
       Vector: Boundary Corner 3
         Position vector of surface intercept in the IAU_PHOEBE frame (km):
            X   =           80.963
            Y   =           76.643
            Z   =           14.427
         Planetocentric coordinates of the intercept (degrees):
            LAT =            7.373
            LON =           43.430
         Phase angle (degrees):                     28.171
         Solar incidence angle (degrees):           21.315
         Emission angle (degrees):                  21.977
 
       Vector: Boundary Corner 4
         Position vector of surface intercept in the IAU_PHOEBE frame (km):
            X   =           81.997
            Y   =           77.106
            Z   =            1.699
         Planetocentric coordinates of the intercept (degrees):
            LAT =            0.865
            LON =           43.239
         Phase angle (degrees):                     28.385
         Solar incidence angle (degrees):           13.882
         Emission angle (degrees):                  21.763
 
       Vector: Cassini NAC Boresight
         Position vector of surface intercept in the IAU_PHOEBE frame (km):
            X   =           86.390
            Y   =           72.089
            Z   =            8.255
         Planetocentric coordinates of the intercept (degrees):
            LAT =            4.196
            LON =           39.844
         Phase angle (degrees):                     28.139
         Solar incidence angle (degrees):           18.247
         Emission angle (degrees):                  17.858
 
         Local Solar Time at boresight intercept (24 Hour Clock):
            11:31:50
 
