EventBasedScheduler.java
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package org.orekit.estimation.measurements.generation;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;
import org.hipparchus.ode.events.Action;
import org.orekit.estimation.measurements.ObservedMeasurement;
import org.orekit.propagation.Propagator;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.AdapterDetector;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.sampling.OrekitStepInterpolator;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.DatesSelector;
import org.orekit.utils.TimeSpanMap;
/** {@link Scheduler} based on {@link EventDetector} for generating measurements sequences.
* <p>
* Event-based schedulers generate measurements following a repetitive pattern when the
* a {@link EventDetector detector} provided at construction is in a {@link SignSemantic
* measurement feasible} state. It is important that the sign of the g function of the underlying
* event detector is not arbitrary, but has a semantic meaning, e.g. in or out,
* true or false. This class works well with event detectors that detect entry to or exit
* from a region, e.g. {@link org.orekit.propagation.events.EclipseDetector EclipseDetector},
* {@link org.orekit.propagation.events.ElevationDetector ElevationDetector}, {@link
* org.orekit.propagation.events.LatitudeCrossingDetector LatitudeCrossingDetector}. Using this
* scheduler with detectors that are not based on entry to or exit from a region, e.g. {@link
* org.orekit.propagation.events.DateDetector DateDetector}, {@link
* org.orekit.propagation.events.LongitudeCrossingDetector LongitudeCrossingDetector}, will likely
* lead to unexpected results.
* </p>
* <p>
* The repetitive pattern can be either a continuous stream of measurements separated by
* a constant step (for example one measurement every 60s), or several sequences of measurements
* at high rate up to a maximum number, with a rest period between sequences (for example
* sequences of up to 256 measurements every 100ms with 300s between each sequence).
* </p>
* @param <T> the type of the measurement
* @author Luc Maisonobe
* @since 9.3
*/
public class EventBasedScheduler<T extends ObservedMeasurement<T>> extends AbstractScheduler<T> {
/** Semantic of the detector g function sign to use. */
private final SignSemantic signSemantic;
/** Feasibility status. */
private TimeSpanMap<Boolean> feasibility;
/** Propagation direction. */
private boolean forward;
/** Simple constructor.
* <p>
* The event detector instance should <em>not</em> be already bound to the propagator.
* It will be wrapped in an {@link AdapterDetector adapter} in order to manage time
* ranges when measurements are feasible. The wrapping adapter will be automatically
* {@link Propagator#addEventDetector(EventDetector) added} to the propagator by this
* constructor.
* </p>
* <p>
* BEWARE! Dates selectors often store internally the last selected dates, so they are not
* reusable across several {@link EventBasedScheduler instances}. A separate selector
* should be used for each scheduler.
* </p>
* @param builder builder for individual measurements
* @param selector selector for dates (beware that selectors are generally not
* reusable across several {@link EventBasedScheduler instances}, each selector should
* be dedicated to one scheduler
* @param propagator propagator associated with this scheduler
* @param detector detector for checking measurements feasibility
* @param signSemantic semantic of the detector g function sign to use
*/
public EventBasedScheduler(final MeasurementBuilder<T> builder, final DatesSelector selector,
final Propagator propagator,
final EventDetector detector, final SignSemantic signSemantic) {
super(builder, selector);
this.signSemantic = signSemantic;
this.feasibility = new TimeSpanMap<Boolean>(Boolean.FALSE);
this.forward = true;
propagator.addEventDetector(new FeasibilityAdapter(detector));
}
/** {@inheritDoc} */
@Override
public SortedSet<T> generate(final List<OrekitStepInterpolator> interpolators) {
// select dates in the current step, using arbitrarily interpolator 0
// as all interpolators cover the same range
final List<AbsoluteDate> dates = getSelector().selectDates(interpolators.get(0).getPreviousState().getDate(),
interpolators.get(0).getCurrentState().getDate());
// generate measurements when feasible
final SortedSet<T> measurements = new TreeSet<>();
for (final AbsoluteDate date : dates) {
if (feasibility.get(date)) {
// a measurement is feasible at this date
// interpolate states at measurement date
final SpacecraftState[] states = new SpacecraftState[interpolators.size()];
for (int i = 0; i < states.length; ++i) {
states[i] = interpolators.get(i).getInterpolatedState(date);
}
// generate measurement
measurements.add(getBuilder().build(states));
}
}
return measurements;
}
/** Adapter for managing feasibility status changes. */
private class FeasibilityAdapter extends AdapterDetector {
/** Build an adaptor wrapping an existing detector.
* @param detector detector to wrap
*/
FeasibilityAdapter(final EventDetector detector) {
super(detector);
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState s0, final AbsoluteDate t) {
super.init(s0, t);
forward = t.compareTo(s0.getDate()) > 0;
feasibility = new TimeSpanMap<Boolean>(signSemantic.measurementIsFeasible(g(s0)));
}
/** {@inheritDoc} */
@Override
public Action eventOccurred(final SpacecraftState s, final boolean increasing) {
// find the feasibility status AFTER the current date
final boolean statusAfter = signSemantic.measurementIsFeasible(increasing ? +1 : -1);
// store either status or its opposite according to propagation direction
if (forward) {
// forward propagation
feasibility.addValidAfter(statusAfter, s.getDate(), false);
} else {
// backward propagation
feasibility.addValidBefore(!statusAfter, s.getDate(), false);
}
// delegate to wrapped detector
return super.eventOccurred(s, increasing);
}
}
}