Module JNISpice
Package spice.basic

Class GFRayInFOVSearch


  • public class GFRayInFOVSearch
    extends GFBinaryStateSearch
    Class GFRayInFOVSearch conducts searches for time intervals over which a specified target body appears in a specified instrument field of view (FOV).

    Code Examples

    The numerical results shown for these examples may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation.

    This example is an extension of example #1 in the header of GFTargetInFOVSearch. The problem statement for that example is

       Search for times when Saturn's satellite Phoebe is within the
       FOV of the Cassini narrow angle camera (CASSINI_ISS_NAC). To
       simplify the problem, restrict the search to a short time
       period where continuous Cassini bus attitude data are
       available.
    
       Use a step size of 10 seconds to reduce chances of missing
       short visibility events.
    

    Here we search the same confinement window for times when a selected background star is visible. We use the FOV of the Cassini ISS wide angle camera (CASSINI_ISS_WAC) to enhance the probability of viewing the star.

    The star we'll use has catalog number 6000 in the Hipparcos Catalog. The star's J2000 right ascension and declination, proper motion, and parallax are taken from that catalog.

    Use the meta-kernel from the GFTargetInFOVSearch example:

       KPL/MK
    
       File name: gftfov_ex1.tm
    
       This meta-kernel is intended to support operation of SPICE
       example programs. The kernels shown here should not be
       assumed to contain adequate or correct versions of data
       required by SPICE-based user applications.
    
       In order for an application to use this meta-kernel, the
       kernels referenced here must be present in the user's
       current working directory.
    
       The names and contents of the kernels referenced
       by this meta-kernel are as follows:
    
          File name                     Contents
          ---------                     --------
          naif0009.tls                  Leapseconds
          cpck05Mar2004.tpc             Satellite orientation and
                                        radii
          981005_PLTEPH-DE405S.bsp      Planetary ephemeris
          020514_SE_SAT105.bsp          Satellite ephemeris
          030201AP_SK_SM546_T45.bsp     Spacecraft ephemeris
          cas_v37.tf                    Cassini FK
          04135_04171pc_psiv2.bc        Cassini bus CK
          cas00084.tsc                  Cassini SCLK kernel
          cas_iss_v09.ti                Cassini IK
    
    
       \begindata
    
          KERNELS_TO_LOAD = ( 'naif0009.tls',
                              'cpck05Mar2004.tpc',
                              '981005_PLTEPH-DE405S.bsp',
                              '020514_SE_SAT105.bsp',
                              '030201AP_SK_SM546_T45.bsp',
                              'cas_v37.tf',
                              '04135_04171pc_psiv2.bc',
                              'cas00084.tsc',
                              'cas_iss_v09.ti'            )
       \begintext
    

    Example code begins here.

       import spice.basic.*;
       import static spice.basic.GFTargetInFOVSearch.*;
       import static spice.basic.AngularUnits.*;
       import static spice.basic.DistanceUnits.*;
       import static spice.basic.TimeConstants.*;
    
       class GFRayInFOVSearchEx1
       {
          //
          // Load the JNISpice shared object library
          // at initialization time.
          //
          static { System.loadLibrary( "JNISpice" ); }
    
          public static void main ( String[] args )
          {
             try {
    
                //
                // Constants
                //
                final String TIMFMT  =
                   "YYYY MON DD HR:MN:SC.###### (TDB)::TDB::RND";
    
                final int    NINTVLS = 100;
    
                //
                // Load kernels.
                //
                KernelDatabase.load ( "gftfov_ex1.tm" );
    
                //
                // Declare the SPICE windows we'll need for the searches
                // and window arithmetic. The result window will be
                // assigned values later; the confinement window must
                // be non-null before it's used.
                //
                SpiceWindow result     = null;
                SpiceWindow cnfine     = new SpiceWindow();
    
                //
                // Declare and assign values to variables required to
                // specify the geometric condition to search for.
                //
    
                //
                // Correct the star direction for stellar aberration when
                // we conduct the search.
                //
                AberrationCorrection abcorr =
                   new AberrationCorrection( "S" );
                Body observer         = new Body ( "Cassini" );
                Instrument inst       = new Instrument ( "CASSINI_ISS_WAC" );
                ReferenceFrame rframe = new ReferenceFrame( "J2000" );
                double stepsz         = 10.0;
    
                //
                // Store the time bounds of our search interval in
                // the `cnfine' confinement window.
                //
                TDBTime et0 = new TDBTime ( "2004 JUN 11 06:30:00 TDB" );
                TDBTime et1 = new TDBTime ( "2004 JUN 11 12:00:00 TDB" );
    
                cnfine.insert( et0.getTDBSeconds(), et1.getTDBSeconds() );
    
                //
                // Create a unit direction vector pointing from observer to star.
                // We'll assume the direction is constant during the confinement
                // window, and we'll use et0 as the epoch at which to compute the
                // direction from the spacecraft to the star.
                //
                // The data below are for the star with catalog number 6000
                // in the Hipparcos catalog. Angular units are degrees; epochs
                // have units of Julian years and have a reference epoch of J1950.
                // The reference frame is J2000.
                //
                int    catno        = 6000;
    
                double parallax_deg = 0.000001056d;
    
                double ra_deg_0     = 19.290789927d;
                double ra_pm        = -0.000000720d;
                double ra_epoch     = 41.2000d;
    
                double dec_deg_0    =  2.015271007d;
                double dec_pm       =  0.000001814d;
                double dec_epoch    = 41.1300d;
    
                //
                // Correct the star's direction for proper motion.
                //
                // The argument t represents et0 as Julian years past J1950.
                //
                JEDTime jed              = new JEDTime( et0 );
                JEDDuration daysPast1950 = jed.sub( new JEDTime(J1950)  );
    
                double t         = daysPast1950.getMeasure()/365.25d;
    
                double dtra      = t - ra_epoch;
                double dtdec     = t - dec_epoch;
    
                double ra_deg    = ra_deg_0  +  dtra  * ra_pm;
                double dec_deg   = dec_deg_0 +  dtdec * dec_pm;
    
                double ra        = ra_deg  * RPD;
                double dec       = dec_deg * RPD;
    
                RADecCoordinates starRADec =
                   new RADecCoordinates ( 1.0, ra, dec );
    
                Vector3 starpos  = starRADec.toRectangular();
    
                //
                // Correct star position for parallax applicable at
                // the Cassini orbiter's position. (The parallax effect
                // is negligible in this case; we're simply demonstrating
                // the computation.)
                //
                double parallax = parallax_deg * RPD;
                double stardist = AU.toKm() / Math.tan(parallax);
    
                //
                // Scale the star's direction vector by its distance from
                // the solar system barycenter. Subtract off the position
                // of the spacecraft relative to the solar system barycenter;
                // the result is the ray's direction vector.
                //
                starpos = starpos.scale( stardist );
    
                PositionVector pos =
                   new PositionVector ( observer,
                                        et0,
                                        new ReferenceFrame( "J2000" ),
                                        new AberrationCorrection("NONE"),
                                        new Body( "solar system barycenter" )  );
    
                Vector3 raydir = starpos.sub( pos );
    
    
                System.out.format ( "%n"                            +
                                    " Instrument:            %s%n"  +
                                    " Star's catalog number: %d%n"  +
                                    "%n",
                                    inst.getName(),
                                    catno                         );
    
                //
                // Create a GF ray in FOV search instance.
                // This instance specifies the geometric condition
                // to be found.
                //
                GFRayInFOVSearch search =
    
                   new GFRayInFOVSearch ( inst,   raydir, rframe,
                                          abcorr, observer        );
                //
                // Run the search.
                //
                // Specify the maximum number of intervals in the result
                // window.
                //
                result = search.run( cnfine, stepsz, NINTVLS );
    
                //
                // Display results.
                //
                int count = result.card();
    
                if ( count == 0 )
                {
                   System.out.format ( "No FOV intersection found.%n" );
                }
                else
                {
                   double[] interval = new double[2];
                   String[] timstr   = new String[2];
    
                   System.out.format
                      ( "  Visibility start time              Stop time%n" );
    
                   for ( int i = 0;  i &lt count;  i++ )
                   {
                      //
                      // Fetch the endpoints of the Ith interval
                      // of the result window.
                      //
                      interval = result.getInterval( i );
    
                      for ( int j = 0;  j &lt 2;  j++ )
                      {
                         timstr[j] = ( new TDBTime(interval[j]) ).toString(TIMFMT);
                      }
    
                      System.out.format( "  %s  %s%n", timstr[0], timstr[1] );
                   }
                }
                System.out.println( "" );
             }
             catch ( SpiceException exc ) {
                exc.printStackTrace();
             }
          }
       }
    

    When run on a PC/Linux/java 1.6.0_14/gcc platform, the output from this program was:

    
       Instrument:            CASSINI_ISS_WAC
       Star's catalog number: 6000
    
        Visibility start time              Stop time
        2004 JUN 11 06:30:00.000000 (TDB)  2004 JUN 11 12:00:00.000000 (TDB)
    
    

    Version 1.0.0 29-DEC-2009 (NJB)