I get an error in EventHandler

Orekit usage
1

Hello everyone. Im trying to calculate TCA and MissDistance with TLE. I get an error in the code I wrote:

java: Main.ClosestApproachDetector is not abstract and does not override abstract method getMaxCheckInterval() in org.orekit.propagation.events.EventDetector

and here is the code:

import org.example.InitializeOrekit;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.data.DataProvidersManager;
import org.orekit.data.ZipJarCrawler;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.frames.FramesFactory;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.analytical.tle.TLE;
import org.orekit.propagation.analytical.tle.TLEPropagator;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.EventsLogger;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnEvent;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.Constants;

import java.io.File;
import java.util.List;

public class Main {
public static void main(String args) {
try {
// Load Orekit data
InitializeOrekit.init();

        // TLE data for two satellites
        String line1_1 = "1 25544U 98067A   20359.54976495  .00000564  00000-0  18836-4 0  9993";
        String line2_1 = "2 25544  51.6431 110.3336 0001414 284.9646 143.1121 15.48941089253832";
        String line1_2 = "1 40958U 15058F   20359.54947222  .00000224  00000-0  77805-5 0  9995";
        String line2_2 = "2 40958  99.0533 161.6354 0013262 280.7981  79.1920 14.62143262436882";

        // Create TLE objects
        TLE tle1 = new TLE(line1_1, line2_1);
        TLE tle2 = new TLE(line1_2, line2_2);

        // Propagators
        TLEPropagator propagator1 = TLEPropagator.selectExtrapolator(tle1);
        TLEPropagator propagator2 = TLEPropagator.selectExtrapolator(tle2);

        // Initial date
        AbsoluteDate initialDate = new AbsoluteDate(2020, 12, 24, 12, 0, 0.000, TimeScalesFactory.getUTC());
        AbsoluteDate finalDate = initialDate.shiftedBy(86400.0); // Propagate for one day

        // Event detector for TCA
        EventsLogger logger = new EventsLogger();
        EventDetector detector = new ClosestApproachDetector(propagator2);
        propagator1.addEventDetector(logger.monitorDetector(detector));

        // Propagate
        propagator1.propagate(initialDate, finalDate);

        // Get TCA events
        List<EventsLogger.LoggedEvent> events = logger.getLoggedEvents();
        if (!events.isEmpty()) {
            AbsoluteDate tcaDate = events.get(0).getState().getDate();
            System.out.println("TCA Date: " + tcaDate);

            // Calculate MissDistance
            SpacecraftState state1 = propagator1.propagate(tcaDate);
            SpacecraftState state2 = propagator2.propagate(tcaDate);
            double missDistance = Vector3D.distance(state1.getPVCoordinates().getPosition(),
                    state2.getPVCoordinates().getPosition());
            System.out.println("MissDistance at TCA: " + missDistance + " meters");
        } else {
            System.out.println("No TCA detected within the propagation period.");
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

// Custom event detector for closest approach
private static class ClosestApproachDetector implements EventDetector {
    private final TLEPropagator targetPropagator;

    public ClosestApproachDetector(TLEPropagator targetPropagator) {
        this.targetPropagator = targetPropagator;
    }

    @Override
    public double g(SpacecraftState state) throws OrekitException {
        SpacecraftState targetState = targetPropagator.propagate(state.getDate());
        return Vector3D.distance(state.getPVCoordinates().getPosition(),
                targetState.getPVCoordinates().getPosition());
    }

    @Override
    public double getThreshold() {
        return 1.0; // Threshold for event detection
    }

    @Override
    public int getMaxIterationCount() {
        return 100;
    }

    @Override
    public double getMaxCheckInterval() {
        return 600.0; // Check interval in seconds
    }

    @Override
    public EventHandler getHandler() {
        return new StopOnEvent();
    }
}

}

2

Since version 12.0, getMaxCheckInterval should return an AdaptableInterval instead of a double.
Also note that returning 1.0 for getThreshold is really huge, something in the ballpark of 1.0e-6 or lesser is generally use.

3

Hi,

On top of what Luc already said, I would add that your handler should be a private final attribute accessed via the getter. Here you’re recreating it at each call of the latter.
Actually you should inherit from AbstractDetector rather than the interface EventDetector directly.

Cheers,
Romain.