Satellite's sub satellite point trajectory within the ground area

[YangYang]

Now I want to define a ground area to obtain the time of the satellite’s sub satellite point trajectory within the area. How should I modify the code. If possible, please provide some specific code. Thank you！
import java.io.File;
import java.util.Locale;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.geometry.spherical.twod.SphericalPolygonsSet;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.data.DataContext;
import org.orekit.data.DataProvidersManager;
import org.orekit.data.DirectoryCrawler;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.frames.FramesFactory;
import org.orekit.models.earth.tessellation.EllipsoidTessellator;
import org.orekit.orbits.KeplerianOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.Propagator;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.analytical.KeplerianPropagator;
import org.orekit.propagation.events.GeographicZoneDetector;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.Constants;
import org.orekit.utils.IERSConventions;
import org.orekit.utils.PVCoordinates;

/** Orekit tutorial for special event detection.

• This tutorial shows how to easily check for visibility between a satellite and a ground station.

• @author Pascal Parraud
  */
  public class RectangularRegionOnEarth {

  /** Private constructor for utility class. */
  private RectangularRegionOnEarth() {
  // empty
  }

  /** Program entry point.

  • @param args program arguments (unused here)
    */
    public static void main(final String args) {
    try {
    // configure Orekit
    final File home = new File(System.getProperty(“user.home”));
    final File orekitData = new File(home, “orekit-data”);
    if (!orekitData.exists()) {
    System.err.format(Locale.US, “Failed to find %s folder%n”,
    orekitData.getAbsolutePath());
    System.err.format(Locale.US, “You need to download %s from %s, unzip it in %s and rename it ‘orekit-data’ for this tutorial to work%n”,
    “orekit-data-master.zip”, “https://gitlab.orekit.org/orekit/orekit-data/-/archive/master/orekit-data-master.zip”,
    home.getAbsolutePath());
    System.exit(1);
    }
    final DataProvidersManager manager = DataContext.getDefault().getDataProvidersManager();
    manager.addProvider(new DirectoryCrawler(orekitData));

     //  Initial state definition : date, orbit
     final AbsoluteDate initialDate = new AbsoluteDate(2023, 10, 26, 8, 00, 00.000, TimeScalesFactory.getUTC());
     final double mu =  3.986004415e+14; // gravitation coefficient
     final Frame inertialFrame = FramesFactory.getEME2000(); // inertial frame for orbit definition
     final Vector3D position  = new Vector3D(-7518565.475, 4279265.668, 4816446.308);
     final Vector3D velocity  = new Vector3D(-5463.904, -5533.9672, 50.719);
     final PVCoordinates pvCoordinates = new PVCoordinates(position, velocity);
     final Orbit initialOrbit = new KeplerianOrbit(pvCoordinates, inertialFrame, initialDate, mu);
    
     // Propagator : consider a simple Keplerian motion 
     final Propagator kepler = new KeplerianPropagator(initialOrbit);
    
     // Earth and frame
     final Frame earthFrame = FramesFactory.getITRF(IERSConventions.IERS_2010, true);
     final BodyShape earth = new OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
                                                  Constants.WGS84_EARTH_FLATTENING,
                                                  earthFrame);
    
     //创建一个地面区域
     GeodeticPoint point1 = new GeodeticPoint(Math.toRadians(0), Math.toRadians(30), 0.0);
     GeodeticPoint point2 = new GeodeticPoint(Math.toRadians(30), Math.toRadians(30), 0.0);
     GeodeticPoint point3 = new GeodeticPoint(Math.toRadians(30), Math.toRadians(0), 0.0);
     GeodeticPoint point4 = new GeodeticPoint(Math.toRadians(0), Math.toRadians(0), 0.0);
    
     // 创建表示地面区域的SphericalPolygonsSet
     SphericalPolygonsSet region = EllipsoidTessellator.buildSimpleZone(1.0e-10, point1, point2, point3, point4);
    
     // Event definition
     final double maxcheck  = 60;
     final double threshold =  0.001;
     final double elevation = FastMath.toRadians(0.0);
      
     final GeographicZoneDetector zoneDetector = new GeographicZoneDetector(maxcheck, threshold, earth, region, elevation)
     		.withHandler((s, detector, increasing) -> {
                 if (!increasing) {
                     System.out.println("Visibility begins at " + s.getDate());
                 } else {
                     System.out.println("Visibility ends at " + s.getDate());
                     System.out.println();
                 }
                 return Action.CONTINUE; // Continue processing the event
             });
    
     // Add event to be detected
     kepler.addEventDetector(zoneDetector);
    
     // Propagate from the initial date to the first raising or for the fixed duration
     final SpacecraftState finalState = kepler.propagate(initialDate.shiftedBy(360000.));
    
     System.out.println(" Final state : " + finalState.getDate().durationFrom(initialDate));
    

    } catch (OrekitException oe) {
    System.err.println(oe.getLocalizedMessage());
    }
    }

}