 
Geometric Event Finding Hands-On Lesson (MATLAB)
===========================================================================
 
   May 12, 2009
 
 
Overview
--------------------------------------------------------
 
   This lesson illustrates how the Geometry Finder (GF) subsystem of the
   Mice Toolkit can be used to find time intervals when specified geometric
   conditions are satisfied.
 
   In this lesson the student is asked to construct a program that finds
   the time intervals, within a specified time range, when the Mars Express
   Orbiter (MEX) is visible from the DSN station DSS-14. Possible
   occultation of the spacecraft by Mars is to be considered.
 
 
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 ``mice/'' tree and
   copy this document to that subdirectory before loading it into a Web
   browser.
 
 
References
--------------------------------------------------------
 
 
Tutorials
 
   The following SPICE tutorials serve as references for the discussions in
   this lesson:
 
 
      Name             Lesson steps/functions 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
      Lunar-Earth PCK  Lunar and Earth Orientation Data
      GF               The SPICE Geometry Ginder (GF) subsystem
 
   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 ``mice/doc'' directory in the MATLAB installation
   tree.
 
      Name             Lesson steps/functions that it describes
      ---------------  -----------------------------------------
      frames.req       Using reference frames
      gf.req           The SPICE geometry finder (GF) subsystem
      kernel.req       Loading SPICE kernels
      naif_ids.req     Body and reference frame names
      pck.req          Obtaining planetary constants data
      spk.req          Computing positions and velocities
      time.req         UTC to ET time conversion
      windows.req      The SPICE window data type
      mice.req         The Mice API
 
 
The Permuted Index
 
   Another useful document distributed with the Toolkit is the permuted
   index. This is located under the ``mice/doc'' directory in the MATLAB
   installation tree.
 
   This text document provides a simple mechanism by which users can
   discover which Mice routines perform functions of interest, as well as
   the names of the source files that contain these routines.
 
 
Mice API Documentation
 
   A Mice routine's specification is found in the API documentation page
   located under ``mice/doc/html/mice''.
 
   For example, the document
 
      mice/doc/html/mice/cspice_str2et.html
 
   describes the cspice_str2et routine.
 
 
Kernels Used
--------------------------------------------------------
 
   The following kernels are used in examples provided in this lesson:
 
      File Name                       Type  Description
      -----------------------         ----  --------------------------
      de405xs.bsp                     SPK   Planetary ephemeris SPK,
                                            subsetted to cover only
                                            time range of interest
      earthstns_itrf93_050714.bsp     SPK   DSN station SPK
      earth_topo_050714.tf            FK    DSN station frame definitions
      earth_000101_060525_060303.bpc  PCK   Binary PCK for Earth
      ORMM__040501000000_00076XS.BSP  SPK   MEX Orbiter trajectory SPK,
                                            subsetted to cover only
                                            time range of interest
      naif0008.tls                    LSK   Generic LSK
      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/
 
 
Mice Routines Used
--------------------------------------------------------
 
   This section provides a summary of the functions 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.)
 
      Name           Function that it performs
      -------------- ---------------------------------------------------
      cspice_furnsh  Loads kernels, individually or listed in meta-kernel
      cspice_gfoclt  Solve for times of occultation or transit
      cspice_gfposc  Solve for times when a position vector coordinate
                     constraint is met
      cspice_rpd     Return number of radians per degree
      cspice_str2et  Converts a time string to ET seconds past J2000
      cspice_timout  Format a time string for output
      cspice_wndifd  Find the difference of two d.p. windows
      cspice_wnfetd  Fetch a specified interval from a d.p. window
      cspice_wninsd  Insert an interval into a d.p. window
 
   Refer to the headers of the various functions listed above, as detailed
   interface specifications are provided with the source code.
 
 
Find View Periods
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Write a program that finds the set of time intervals, within the time
   range
 
      2004 MAY 2 TDB
      2004 MAY 6 TDB
 
   when the Mars Express Orbiter (MEX) is visible from the DSN station
   DSS-14. These time intervals are frequently called ``view periods.''
 
   The spacecraft is considered visible if its apparent position (that is,
   its position corrected for light time and stellar aberration) has
   elevation of at least 6 degrees in the topocentric reference frame
   DSS-14_TOPO. In this exercise, we ignore the possibility of occultation
   of the spacecraft by Mars.
 
   Use a search step size that ensures that no view periods of duration 5
   minutes or longer will be missed by the search.
 
   Display the start and stop times of these intervals using TDB calendar
   dates and millisecond precision.
 
 
Learning Goals
--------------------------------------------------------
 
   Exposure to SPICE GF event finding routines. Familiarity with SPICE
   windows and routines that manipulate them. Exposure to SPICE time
   parsing and output formatting routines.
 
 
Approach
--------------------------------------------------------
 
 
Solution steps
 
   A possible solution could consist of the following steps:
 
   Preparation:
 
       1.   Decide what SPICE kernels are necessary. Use the SPICE summary
            tool BRIEF to examine the coverage of the binary kernels and
            verify the availability of required data.
 
       2.   Create a meta-kernel listing the SPICE kernels to be loaded.
            (Hint: consult a programming example tutorial, or the
            Introduction to Kernels tutorial, for a reminder of how to do
            this.)
 
            Name the meta-kernel 'viewpr.tm'.
 
   Next, write a program that performs the following steps:
 
       1.   Use cspice_furnsh to load the meta-kernel.
 
       2.   Use cspice_wninsd to create a Mice confinement window
            ```cnfine''' to hold the time period within which the search is
            to be conducted: insert the given time bounds into the
            confinement window using cspice_wninsd.
 
       3.   Select a step size for searching for visibility state
            transitions: in this case, each target rise or set event is a
            state transition.
 
            The step size must be large enough so the search proceeds with
            reasonable speed, but small enough so that no visibility
            transition events---that is, target rise or set events---are
            missed.
 
       4.   Use the GF routine cspice_gfposc to find the window of times,
            within the confinement window `cnfine', during which the MEX
            spacecraft is above the elevation limit as seen from DSN
            station DSS-14, in the the reference frame DSS-14_TOPO.
 
            Use light time and stellar aberration corrections for the
            apparent position of the spacecraft as seen from the station.
 
       5.   Fetch and display the contents of the result window. Use
            cspice_wnfetd to extract from the result window the start and
            stop times of each time interval. Display each of the intervals
            in the result window as a pair of start and stop times. Express
            each time as a TDB calendar date using the routine
            cspice_timout.
 
   You may find it useful to consult the references listed above. In
   particular, the header of the SPICE GF function cspice_gfposc contains
   pertinent documentation.
 
 
Solution
--------------------------------------------------------
 
 
Solution Meta-Kernel
 
   The meta-kernel we created for the solution to this exercise is named
   'viewpr.tm'. Its contents follow:
 
 
      KPL/MK
 
         Example meta-kernel for geometric event finding hands-on
         coding lesson.
 
            Version 2.0.0 15-MAR-2008 (NJB)
 
 
         Identify names of kernels to load:
 
      \begindata
 
         KERNELS_TO_LOAD = (
 
                 'kernels/spk/de405xs.bsp'
                 'kernels/spk/earthstns_itrf93_050714.bsp'
                 'kernels/fk/earth_topo_050714.tf'
                 'kernels/pck/earth_000101_060525_060303.bpc'
                 'kernels/lsk/naif0008.tls'
                 'kernels/spk/ORMM__040501000000_00076XS.BSP'
                 'kernels/pck/pck00008.tpc'
                           )
 
      \begintext
 
 
 
Solution Code
 
   The example program below shows one possible solution.
 
 
      %
      % Find and display the window of times when the MEX
      % spacecraft is above a specified elevation limit in the
      % topocentric reference frame of DSN station DSS-14.
      %
      function viewpr_m()
 
      %
      % The meta-kernel:
      %
      META   = 'viewpr.tm';
 
      %
      % Maximum number of intervals in any window:
      %
      MAXIVL = 1000;
 
      %
      % Time string length:
      %
      TIMLEN = 50;
 
      %
      % Format string for time output:
      %
      TDBFMT = 'YYYY MON DD HR:MN:SC.### (TDB) ::TDB';
 
      %
      % Load the meta-kernel.
      %
      cspice_furnsh( META );
 
      %
      % Assign the inputs for our search.
      %
      % Since we're interested in the apparent location of the
      % target, we use light time and stellar aberration
      % corrections. We use the "converged Newtonian" form
      % of the light time correction because this choice may
      % increase the accuracy of the occultation times we'll
      % compute using cspice_gfoclt.
      %
      srfpt  = 'DSS-14';
      obsfrm = 'DSS-14_TOPO';
      target = 'MEX';
      abcorr = 'CN+S';
      start  = '2004 MAY 2 TDB';
      stop   = '2004 MAY 6 TDB';
      elvlim =  6.0;
 
      %
      % The elevation limit above has units of degrees; we convert
      % this value to radians for computation using SPICE routines.
      % We'll store the equivalent value in radians in REVLIM.
      %
      revlim = cspice_rpd() * elvlim;
 
      %
      % Since SPICE doesn't directly support the AZ/EL coordinate
      % system, we use the equivalent constraint
      %
      %    latitude > REVLIM
      %
      % in the latitudinal coordinate system, where the reference
      % frame is topocentric and is centered at the viewing location.
      %
      crdsys = 'LATITUDINAL';
      coord  = 'LATITUDE';
      relate = '>';
 
      %
      % The adjustment value only applies to absolute extrema
      % searches; simply give it an initial value of zero
      % for this inequality search.
      %
      adjust = 0.0;
 
      %
      % STEPSZ is the step size, measured in seconds, used to search
      % for times bracketing a state transition. Since we don't expect
      % any events of interest to be shorter than five minutes, and
      % since the separation between events is well over 5 minutes,
      % we'll use this value as our step size. Units are seconds.
      %
      stepsz = 300.0;
 
      %
      % Display a banner for the output report:
      %
 
      disp( ' ' );
      disp( 'Inputs for target visibility search:' );
      disp( ' ' );
 
      fprintf( '   Target                       = %s\n',  target );
      fprintf( '   Observation surface location = %s\n',  srfpt  );
      fprintf( '   Observer''s reference frame   = %s\n', obsfrm );
      fprintf( '   Elevation limit (degrees)    = %f\n',  elvlim );
      fprintf( '   Aberration correction        = %s\n',  abcorr );
      fprintf( '   Step size (seconds)          = %f\n',  stepsz );
 
      %
      % Convert the start and stop times to ET.
      %
      etbeg = cspice_str2et( start );
      etend = cspice_str2et( stop  );
 
      %
      % Display the search interval start time and stop
      % times using the format shown below.
      %
      %     2004 MAY 06 20:15:00.000 (TDB)
      %
      timstr0 = cspice_timout( etbeg, TDBFMT );
      timstr1 = cspice_timout( etend, TDBFMT );
 
      fprintf( '   Start time                   = %s\n', timstr0 );
      fprintf( '   Stop time                    = %s\n', timstr1 );
      disp( ' ' );
 
      %
      % Create the "confinement" window; store in this window
      % the interval over which we'll conduct the search.
      %
      cnfine = cspice_wninsd( etbeg, etend );
 
      %
      % In the call below, the maximum number of window
      % intervals cspice_gfposc can store internally is
      % set to MAXIVL. We'll also use MAXIVL as the maximum
      % number of intervals in the result window.
      %
      % Now search for the time period, within our confinement
      % window, during which the apparent target has elevation
      % at least equal to the elevation limit.
      %
      riswin = cspice_gfposc ( target, obsfrm, abcorr, srfpt,  ...
                               crdsys, coord,  relate, revlim, ...
                               adjust, stepsz, MAXIVL, cnfine     );
 
      %
      % Let winsiz contain the number of intervals
      % in the SPICE window riswin.
      %
      winsiz = length( riswin )/2;
 
      %
      % Display the rise and set times.
      %
 
      if  winsiz == 0
 
         disp( 'No events were found.' );
 
      else
 
         %
         %  Display the visibility time periods.
         %
         fprintf( [ 'Visibility times of %s '  ...
                    'as seen from %s:\n\n' ], target, srfpt );
 
         for i = 1:winsiz
 
            %
            % Fetch the Ith interval from the window.
            %
            [intbeg, intend] = cspice_wnfetd( riswin, i );
 
            %
            % Convert the rise time to a TDB calendar string.
            %
            timstr = cspice_timout( intbeg, TDBFMT );
 
            %
            % Write the string to standard output.
            %
            if  i == 1
 
               line = 'Visibility or window start time:  ';
 
            else
 
               line = 'Visibility start time:            ';
 
            end
 
            fprintf( '%s%s\n', line, timstr );
 
            %
            % Convert the set time to a TDB calendar string.
            %
            timstr = cspice_timout( intend, TDBFMT );
 
            %
            % Write the string to standard output.
            %
            if  i == winsiz
 
               line = 'Visibility or window stop time:   ';
 
            else
 
               line = 'Visibility stop time:             ';
 
            end
 
            fprintf( '%s%s\n\n', line, timstr );
 
         end
 
      end
 
      %
      % Unload kernels so they're not accidentally used by another
      % SPICE-based program during the current IDL session.
      %
      cspice_kclear;
 
      %
      % End of function viewpr
      %
 
 
Solution Sample Output
 
   Numerical results shown for this example may differ across platforms
   since the results depend on the SPICE kernels used as input and on the
   host platform's arithmetic implementation.
 
   Execute the program. The output is:
 
 
 
      Inputs for target visibility search:
 
         Target                       = MEX
         Observation surface location = DSS-14
         Observer's reference frame   = DSS-14_TOPO
         Elevation limit (degrees)    = 6.000000
         Aberration correction        = CN+S
         Step size (seconds)          = 300.000000
         Start time                   = 2004 MAY 02 00:00:00.000 (TDB)
         Stop time                    = 2004 MAY 06 00:00:00.000 (TDB)
 
      Visibility times of MEX as seen from DSS-14:
 
      Visibility or window start time:  2004 MAY 02 00:00:00.000 (TDB)
      Visibility stop time:             2004 MAY 02 05:35:03.096 (TDB)
 
      Visibility start time:            2004 MAY 02 16:09:14.078 (TDB)
      Visibility stop time:             2004 MAY 03 05:33:57.257 (TDB)
 
      Visibility start time:            2004 MAY 03 16:08:02.279 (TDB)
      Visibility stop time:             2004 MAY 04 05:32:50.765 (TDB)
 
      Visibility start time:            2004 MAY 04 16:06:51.259 (TDB)
      Visibility stop time:             2004 MAY 05 05:31:43.600 (TDB)
 
      Visibility start time:            2004 MAY 05 16:05:40.994 (TDB)
      Visibility or window stop time:   2004 MAY 06 00:00:00.000 (TDB)
 
 
 
Find Times when Target is Visible
===========================================================================
 
 
Task Statement
--------------------------------------------------------
 
   Extend the program of the previous chapter to find times when the MEX
   orbiter is:
 
       --   Above the elevation limit in the DSS-14_TOPO topocentric
            reference frame.
 
       --   and is not occulted by Mars
 
   Store the set of time intervals when the spacecraft is visible in a Mice
   window. We'll call this the ``result window.''
 
   Display each of the intervals in the result window as a pair of start
   and stop times. Express each time as a TDB calendar date using the same
   format as in the previous program.
 
 
Learning Goals
--------------------------------------------------------
 
   Familiarity with the GF occultation finding routine cspice_gfoclt.
   Further experience with the Mice window functions.
 
 
Approach
--------------------------------------------------------
 
 
Solution steps
 
   A possible solution would consist of the following steps:
 
       1.   Use the meta-kernel of the previous lesson.
 
       2.   Include the code from the program of the previous chapter in a
            new source file; modify this code to create the new program.
 
       3.   Search for occultations of the MEX orbiter as seen from DSS-14
            using cspice_gfoclt. Use as the confinement window for this
            search the result window from the elevation search performed by
            cspice_gfposc.
 
            Since occultations occur when the apparent MEX spacecraft
            position is behind the apparent figure of Mars, light time
            correction must be performed for the occultation search. To
            improve accuracy of the occultation state determination, use
            ``converged Newtonian'' light time correction.
 
       4.   Use the Mice window subtraction routine cspice_wndifd to
            subtract the window of times when the spacecraft is occulted
            from the window of times when the spacecraft is above the
            elevation limit. The difference window `viswin' is the final
            result.
 
       5.   Modify the code to display the contents of the window `viswin'.
 
   This completes the assignment.
 
 
Solution
--------------------------------------------------------
 
 
Solution Code
 
 
      %
      % Find and display the window of times when the MEX
      % spacecraft is above a specified elevation limit in the
      % topocentric reference frame of DSN station DSS-14
      % and is not occulted by Mars.
      %
      function visibl_m()
 
      %
      % The meta-kernel:
      %
      META   = 'viewpr.tm';
 
      %
      % Maximum number of intervals in any window:
      %
      MAXIVL = 1000;
 
      %
      % Time string length:
      %
      TIMLEN = 50;
 
      %
      % Format string for time output:
      %
      TDBFMT = 'YYYY MON DD HR:MN:SC.### (TDB) ::TDB';
 
      %
      % Load the meta-kernel.
      %
      cspice_furnsh( META );
 
      %
      % Assign the inputs for our search.
      %
      % Since we're interested in the apparent location of the
      % target, we use light time and stellar aberration
      % corrections. We use the "converged Newtonian" form
      % of the light time correction because this choice may
      % increase the accuracy of the occultation times we'll
      % compute using cspice_gfoclt.
      %
      srfpt  = 'DSS-14';
      obsfrm = 'DSS-14_TOPO';
      target = 'MEX';
      abcorr = 'CN+S';
      start  = '2004 MAY 2 TDB';
      stop   = '2004 MAY 6 TDB';
      elvlim =  6.0;
 
      %
      % The elevation limit above has units of degrees; we convert
      % this value to radians for computation using SPICE routines.
      % We'll store the equivalent value in radians in REVLIM.
      %
      revlim = cspice_rpd() * elvlim;
 
 
      %
      % We model the target shape as a point and the blocking body's
      % shape as an ellipsoid. No body-fixed reference frame is
      % required for the target since its orientation is not used.
      %
      back   = target;
      bshape = 'POINT';
      bframe = ' ';
      front  = 'MARS';
      fshape = 'ELLIPSOID';
      fframe = 'IAU_MARS';
 
      %
      % The occultation type should be set to 'ANY' for a point
      % target.
      %
      occtyp = 'any';
 
      %
      % Since SPICE doesn't directly support the AZ/EL coordinate
      % system, we use the equivalent constraint
      %
      %    latitude > REVLIM
      %
      % in the latitudinal coordinate system, where the reference
      % frame is topocentric and is centered at the viewing location.
      %
      crdsys = 'LATITUDINAL';
      coord  = 'LATITUDE';
      relate = '>';
 
      %
      % The adjustment value only applies to absolute extrema
      % searches; simply give it an initial value of zero
      % for this inequality search.
      %
      adjust = 0.0;
 
      %
      % STEPSZ is the step size, measured in seconds, used to search
      % for times bracketing a state transition. Since we don't expect
      % any events of interest to be shorter than five minutes, and
      % since the separation between events is well over 5 minutes,
      % we'll use this value as our step size. Units are seconds.
      %
      stepsz = 300.0;
 
      %
      % Display a banner for the output report:
      %
 
      disp( ' ' );
      disp( 'Inputs for target visibility search:' );
      disp( ' ' );
 
      fprintf( '   Target                       = %s\n',  target );
      fprintf( '   Observation surface location = %s\n',  srfpt  );
      fprintf( '   Observer''s reference frame   = %s\n', obsfrm );
      fprintf( '   Blocking body                = %s\n',  front  );
      fprintf( '   Blocker''s reference frame    = %s\n', fframe );
      fprintf( '   Elevation limit (degrees)    = %f\n',  elvlim );
      fprintf( '   Aberration correction        = %s\n',  abcorr );
      fprintf( '   Step size (seconds)          = %f\n',  stepsz );
 
      %
      % Convert the start and stop times to ET.
      %
      etbeg = cspice_str2et( start );
      etend = cspice_str2et( stop  );
 
      %
      % Display the search interval start time and stop
      % times using the format shown below.
      %
      %     2004 MAY 06 20:15:00.000 (TDB)
      %
      timstr0 = cspice_timout( etbeg, TDBFMT );
      timstr1 = cspice_timout( etend, TDBFMT );
 
      fprintf( '   Start time                   = %s\n', timstr0 );
      fprintf( '   Stop time                    = %s\n', timstr1 );
      disp( ' ' );
 
      %
      % Create the "confinement" window; store in this window
      % the interval over which we'll conduct the search.
      %
      cnfine = cspice_wninsd( etbeg, etend );
 
      %
      % In the call below, the maximum number of window
      % intervals cspice_gfposc can store internally is
      % set to MAXIVL. We'll also use MAXIVL as the maximum
      % number of intervals in the result window.
      %
      % Now search for the time period, within our confinement
      % window, during which the apparent target has elevation
      % at least equal to the elevation limit.
      %
      riswin = cspice_gfposc ( target, obsfrm, abcorr, srfpt,  ...
                               crdsys, coord,  relate, revlim, ...
                               adjust, stepsz, MAXIVL, cnfine      );
      %
      % Now find the times when the apparent target is above
      % the elevation limit and is not occulted by the
      % blocking body (Mars). We'll find the window of times when
      % the target is above the elevation limit and *is* occulted,
      % then subtract that window from the view period window
      % riswin found above.
      %
      % For this occultation search, we can use riswin as
      % the confinement window because we're not interested in
      % occultations that occur when the target is below the
      % elevation limit.
      %
      % Find occultations within the view period window.
      %
      occwin = cspice_gfoclt( occtyp, front,  fshape,  fframe, ...
                              back,   bshape, bframe,  abcorr, ...
                              srfpt,  stepsz, riswin,  MAXIVL     );
 
      %
      % Subtract the occultation window from the view period
      % window: this yields the time periods when the target
      % is visible.
      %
      viswin = cspice_wndifd( riswin, occwin );
 
      %
      % Let winsiz contain the number of intervals
      % in the SPICE window riswin.
      %
      winsiz = length( viswin )/2;
 
      %
      % Display the rise and set times.
      %
 
      if  winsiz == 0
 
         disp( 'No events were found.' );
 
      else
 
         %
         %  Display the visibility time periods.
         %
         fprintf( [ 'Visibility times of %s '  ...
                    'as seen from %s:\n\n' ], target, srfpt );
 
         for i = 1:winsiz
 
            %
            % Fetch the Ith interval from the window.
            %
            [intbeg, intend] = cspice_wnfetd( viswin, i );
 
            %
            % Convert the rise time to a TDB calendar string.
            %
            timstr = cspice_timout( intbeg, TDBFMT );
 
            %
            % Write the string to standard output.
            %
            if  i == 1
 
               line = 'Visibility or window start time:  ';
 
            else
 
               line = 'Visibility start time:            ';
 
            end
 
            fprintf( '%s%s\n', line, timstr );
 
            %
            % Convert the set time to a TDB calendar string.
            %
            timstr = cspice_timout( intend, TDBFMT );
 
            %
            % Write the string to standard output.
            %
            if  i == winsiz
 
               line = 'Visibility or window stop time:   ';
 
            else
 
               line = 'Visibility stop time:             ';
 
            end
 
            fprintf( '%s%s\n\n', line, timstr );
 
         end
 
      end
 
      %
      % Unload kernels so they're not accidentally used by another
      % SPICE-based program during the current MATLAB session.
      %
      cspice_kclear;
 
      %
      % End of function visibl
      %
 
 
Solution Sample Output
 
   Numerical results shown for this example may differ across platforms
   since the results depend on the SPICE kernels used as input and on the
   host platform's arithmetic implementation.
 
   Execute the program. The output is:
 
 
      Inputs for target visibility search:
 
         Target                       = MEX
         Observation surface location = DSS-14
         Observer's reference frame   = DSS-14_TOPO
         Blocking body                = MARS
         Blocker's reference frame    = IAU_MARS
         Elevation limit (degrees)    = 6.000000
         Aberration correction        = CN+S
         Step size (seconds)          = 300.000000
         Start time                   = 2004 MAY 02 00:00:00.000 (TDB)
         Stop time                    = 2004 MAY 06 00:00:00.000 (TDB)
 
      Visibility times of MEX as seen from DSS-14:
 
      Visibility or window start time:  2004 MAY 02 00:00:00.000 (TDB)
      Visibility stop time:             2004 MAY 02 04:49:30.827 (TDB)
 
      Visibility start time:            2004 MAY 02 16:09:14.078 (TDB)
      Visibility stop time:             2004 MAY 02 20:00:22.514 (TDB)
 
      Visibility start time:            2004 MAY 02 21:01:38.222 (TDB)
      Visibility stop time:             2004 MAY 03 03:35:42.256 (TDB)
 
      Visibility start time:            2004 MAY 03 04:36:42.484 (TDB)
      Visibility stop time:             2004 MAY 03 05:33:57.257 (TDB)
 
      Visibility start time:            2004 MAY 03 16:08:02.279 (TDB)
      Visibility stop time:             2004 MAY 03 18:46:26.013 (TDB)
 
      Visibility start time:            2004 MAY 03 19:46:54.618 (TDB)
      Visibility stop time:             2004 MAY 04 02:21:44.562 (TDB)
 
      Visibility start time:            2004 MAY 04 03:21:56.347 (TDB)
      Visibility stop time:             2004 MAY 04 05:32:50.765 (TDB)
 
      Visibility start time:            2004 MAY 04 16:06:51.259 (TDB)
      Visibility stop time:             2004 MAY 04 17:32:25.809 (TDB)
 
      Visibility start time:            2004 MAY 04 18:32:05.975 (TDB)
      Visibility stop time:             2004 MAY 05 01:07:48.264 (TDB)
 
      Visibility start time:            2004 MAY 05 02:07:11.601 (TDB)
      Visibility stop time:             2004 MAY 05 05:31:43.600 (TDB)
 
      Visibility start time:            2004 MAY 05 16:05:40.994 (TDB)
      Visibility stop time:             2004 MAY 05 16:18:35.560 (TDB)
 
      Visibility start time:            2004 MAY 05 17:17:27.717 (TDB)
      Visibility or window stop time:   2004 MAY 05 23:54:04.672 (TDB)
 
 
