Hello, could you please explain in detail what this code means? Although I can run this code, I am not clear about the specific meaning, so I am unable to conduct further experiments.
public class InAreaStatus implements EventHandler {
private boolean inArea = false;
public Action eventOccurred(SpacecraftState s, EventDetector detector, boolean increasing) {
if (!increasing) {
System.out.println("Visibility begins at " + s.getDate());
inArea = true;
} else {
System.out.println("Visibility ends at " + s.getDate());
System.out.println();
inArea = false;
}
return Action.CONTINUE;
}
public boolean inArea() {
return inArea;
}
}
public class SubPointWriter implements OrekitFixedStepHandler {
private final InAreaStatus status;
private final OneAxisEllipsoid earth;
public SubPointWriter(final InAreaStatus status, final BodyShape earth2) {
this.status = status;
this.earth = (OneAxisEllipsoid) earth2;
}
public void handleStep(SpacecraftState state) {
if (status.inArea()) {
// we only print satellite sub-point when we know we already are in the area of interest
GeodeticPoint gp = earth.transform(state.getPVCoordinates().getPosition(),
state.getFrame(),
state.getDate());
System.out.format(Locale.US, "%s %10.5f %10.5f%n",
state.getDate(),
FastMath.toDegrees(gp.getLatitude()),
FastMath.toDegrees(gp.getLongitude()));
}
}
}
public class Test {
public static void main(String args[]) {
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 double stepSize = 100;
final InAreaStatus status = new InAreaStatus();
final GeographicZoneDetector zoneDetector =
new GeographicZoneDetector(maxcheck, threshold, earth, region, elevation)
.withHandler(status);
final SubPointWriter subPointWriter = new SubPointWriter(status, earth);
kepler.addEventDetector(zoneDetector);
kepler.getMultiplexer().add(stepSize, subPointWriter);
kepler.propagate(initialDate.shiftedBy(36000.));
}
}