AbstractAnalyticalPropagator.java
/* Copyright 2002-2020 CS GROUP
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* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.propagation.analytical;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;
import org.hipparchus.exception.MathRuntimeException;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.orekit.attitudes.Attitude;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.frames.Frame;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.AbstractPropagator;
import org.orekit.propagation.AdditionalStateProvider;
import org.orekit.propagation.BoundedPropagator;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.EventState;
import org.orekit.propagation.events.EventState.EventOccurrence;
import org.orekit.propagation.sampling.OrekitStepInterpolator;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedPVCoordinates;
/** Common handling of {@link org.orekit.propagation.Propagator} methods for analytical propagators.
* <p>
* This abstract class allows to provide easily the full set of {@link
* org.orekit.propagation.Propagator Propagator} methods, including all propagation
* modes support and discrete events support for any simple propagation method. Only
* two methods must be implemented by derived classes: {@link #propagateOrbit(AbsoluteDate)}
* and {@link #getMass(AbsoluteDate)}. The first method should perform straightforward
* propagation starting from some internally stored initial state up to the specified target date.
* </p>
* @author Luc Maisonobe
*/
public abstract class AbstractAnalyticalPropagator extends AbstractPropagator {
/** Provider for attitude computation. */
private PVCoordinatesProvider pvProvider;
/** Start date of last propagation. */
private AbsoluteDate lastPropagationStart;
/** End date of last propagation. */
private AbsoluteDate lastPropagationEnd;
/** Initialization indicator of events states. */
private boolean statesInitialized;
/** Indicator for last step. */
private boolean isLastStep;
/** Event steps. */
private final Collection<EventState<?>> eventsStates;
/** Build a new instance.
* @param attitudeProvider provider for attitude computation
*/
protected AbstractAnalyticalPropagator(final AttitudeProvider attitudeProvider) {
setAttitudeProvider(attitudeProvider);
pvProvider = new LocalPVProvider();
lastPropagationStart = AbsoluteDate.PAST_INFINITY;
lastPropagationEnd = AbsoluteDate.FUTURE_INFINITY;
statesInitialized = false;
eventsStates = new ArrayList<EventState<?>>();
}
/** {@inheritDoc} */
public BoundedPropagator getGeneratedEphemeris() {
return new BoundedPropagatorView(lastPropagationStart, lastPropagationEnd);
}
/** {@inheritDoc} */
public <T extends EventDetector> void addEventDetector(final T detector) {
eventsStates.add(new EventState<T>(detector));
}
/** {@inheritDoc} */
public Collection<EventDetector> getEventsDetectors() {
final List<EventDetector> list = new ArrayList<EventDetector>();
for (final EventState<?> state : eventsStates) {
list.add(state.getEventDetector());
}
return Collections.unmodifiableCollection(list);
}
/** {@inheritDoc} */
public void clearEventsDetectors() {
eventsStates.clear();
}
/** {@inheritDoc} */
public SpacecraftState propagate(final AbsoluteDate start, final AbsoluteDate target) {
try {
initializePropagation();
lastPropagationStart = start;
final double dt = target.durationFrom(start);
final double epsilon = FastMath.ulp(dt);
SpacecraftState state = updateAdditionalStates(basicPropagate(start));
// evaluate step size
final double stepSize;
if (getMode() == MASTER_MODE) {
if (Double.isNaN(getFixedStepSize())) {
stepSize = FastMath.copySign(state.getKeplerianPeriod() / 100, dt);
} else {
stepSize = FastMath.copySign(getFixedStepSize(), dt);
}
} else {
stepSize = dt;
}
// initialize event detectors
for (final EventState<?> es : eventsStates) {
es.init(state, target);
}
// initialize step handler
if (getStepHandler() != null) {
getStepHandler().init(state, target);
}
// iterate over the propagation range
statesInitialized = false;
isLastStep = false;
do {
// go ahead one step size
final SpacecraftState previous = state;
AbsoluteDate t = previous.getDate().shiftedBy(stepSize);
if ((dt == 0) || ((dt > 0) ^ (t.compareTo(target) <= 0)) ||
(FastMath.abs(target.durationFrom(t)) <= epsilon)) {
// current step exceeds target
// or is target to within double precision
t = target;
}
final SpacecraftState current = updateAdditionalStates(basicPropagate(t));
final OrekitStepInterpolator interpolator = new BasicStepInterpolator(dt >= 0, previous, current);
// accept the step, trigger events and step handlers
state = acceptStep(interpolator, target, epsilon);
// Update the potential changes in the spacecraft state due to the events
// especially the potential attitude transition
state = updateAdditionalStates(basicPropagate(state.getDate()));
} while (!isLastStep);
// return the last computed state
lastPropagationEnd = state.getDate();
setStartDate(state.getDate());
return state;
} catch (MathRuntimeException mrte) {
throw OrekitException.unwrap(mrte);
}
}
/** Accept a step, triggering events and step handlers.
* @param interpolator interpolator for the current step
* @param target final propagation time
* @param epsilon threshold for end date detection
* @return state at the end of the step
* @exception MathRuntimeException if an event cannot be located
*/
protected SpacecraftState acceptStep(final OrekitStepInterpolator interpolator,
final AbsoluteDate target, final double epsilon)
throws MathRuntimeException {
SpacecraftState previous = interpolator.getPreviousState();
final SpacecraftState current = interpolator.getCurrentState();
OrekitStepInterpolator restricted = interpolator;
// initialize the events states if needed
if (!statesInitialized) {
if (!eventsStates.isEmpty()) {
// initialize the events states
for (final EventState<?> state : eventsStates) {
state.reinitializeBegin(interpolator);
}
}
statesInitialized = true;
}
// search for next events that may occur during the step
final int orderingSign = interpolator.isForward() ? +1 : -1;
final Queue<EventState<?>> occurringEvents = new PriorityQueue<>(new Comparator<EventState<?>>() {
/** {@inheritDoc} */
@Override
public int compare(final EventState<?> es0, final EventState<?> es1) {
return orderingSign * es0.getEventDate().compareTo(es1.getEventDate());
}
});
boolean doneWithStep = false;
resetEvents:
do {
// Evaluate all event detectors for events
occurringEvents.clear();
for (final EventState<?> state : eventsStates) {
if (state.evaluateStep(interpolator)) {
// the event occurs during the current step
occurringEvents.add(state);
}
}
do {
eventLoop:
while (!occurringEvents.isEmpty()) {
// handle the chronologically first event
final EventState<?> currentEvent = occurringEvents.poll();
// get state at event time
SpacecraftState eventState = restricted.getInterpolatedState(currentEvent.getEventDate());
// try to advance all event states to current time
for (final EventState<?> state : eventsStates) {
if (state != currentEvent && state.tryAdvance(eventState, interpolator)) {
// we need to handle another event first
// remove event we just updated to prevent heap corruption
occurringEvents.remove(state);
// add it back to update its position in the heap
occurringEvents.add(state);
// re-queue the event we were processing
occurringEvents.add(currentEvent);
continue eventLoop;
}
}
// all event detectors agree we can advance to the current event time
final EventOccurrence occurrence = currentEvent.doEvent(eventState);
final Action action = occurrence.getAction();
isLastStep = action == Action.STOP;
if (isLastStep) {
// ensure the event is after the root if it is returned STOP
// this lets the user integrate to a STOP event and then restart
// integration from the same time.
eventState = interpolator.getInterpolatedState(occurrence.getStopDate());
restricted = restricted.restrictStep(previous, eventState);
}
// handle the first part of the step, up to the event
if (getStepHandler() != null) {
getStepHandler().handleStep(restricted, isLastStep);
}
if (isLastStep) {
// the event asked to stop integration
return eventState;
}
if (action == Action.RESET_DERIVATIVES || action == Action.RESET_STATE) {
// some event handler has triggered changes that
// invalidate the derivatives, we need to recompute them
final SpacecraftState resetState = occurrence.getNewState();
if (resetState != null) {
resetIntermediateState(resetState, interpolator.isForward());
return resetState;
}
}
// at this point action == Action.CONTINUE or Action.RESET_EVENTS
// prepare handling of the remaining part of the step
previous = eventState;
restricted = new BasicStepInterpolator(restricted.isForward(), eventState, current);
if (action == Action.RESET_EVENTS) {
continue resetEvents;
}
// at this point action == Action.CONTINUE
// check if the same event occurs again in the remaining part of the step
if (currentEvent.evaluateStep(restricted)) {
// the event occurs during the current step
occurringEvents.add(currentEvent);
}
}
// last part of the step, after the last event. Advance all detectors to
// the end of the step. Should only detect a new event here if an event
// modified the g function of another detector. Detecting such events here
// is unreliable and RESET_EVENTS should be used instead. Might as well
// re-check here because we have to loop through all the detectors anyway
// and the alternative is to throw an exception.
for (final EventState<?> state : eventsStates) {
if (state.tryAdvance(current, interpolator)) {
occurringEvents.add(state);
}
}
} while (!occurringEvents.isEmpty());
doneWithStep = true;
} while (!doneWithStep);
isLastStep = target.equals(current.getDate());
// handle the remaining part of the step, after all events if any
if (getStepHandler() != null) {
getStepHandler().handleStep(interpolator, isLastStep);
}
return current;
}
/** Get the mass.
* @param date target date for the orbit
* @return mass mass
*/
protected abstract double getMass(AbsoluteDate date);
/** Get PV coordinates provider.
* @return PV coordinates provider
*/
public PVCoordinatesProvider getPvProvider() {
return pvProvider;
}
/** Reset an intermediate state.
* @param state new intermediate state to consider
* @param forward if true, the intermediate state is valid for
* propagations after itself
*/
protected abstract void resetIntermediateState(SpacecraftState state, boolean forward);
/** Extrapolate an orbit up to a specific target date.
* @param date target date for the orbit
* @return extrapolated parameters
*/
protected abstract Orbit propagateOrbit(AbsoluteDate date);
/** Propagate an orbit without any fancy features.
* <p>This method is similar in spirit to the {@link #propagate} method,
* except that it does <strong>not</strong> call any handler during
* propagation, nor any discrete events, not additional states. It always
* stop exactly at the specified date.</p>
* @param date target date for propagation
* @return state at specified date
*/
protected SpacecraftState basicPropagate(final AbsoluteDate date) {
try {
// evaluate orbit
final Orbit orbit = propagateOrbit(date);
// evaluate attitude
final Attitude attitude =
getAttitudeProvider().getAttitude(pvProvider, date, orbit.getFrame());
// build raw state
return new SpacecraftState(orbit, attitude, getMass(date));
} catch (OrekitException oe) {
throw new OrekitException(oe);
}
}
/** Internal PVCoordinatesProvider for attitude computation. */
private class LocalPVProvider implements PVCoordinatesProvider {
/** {@inheritDoc} */
public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame) {
return propagateOrbit(date).getPVCoordinates(frame);
}
}
/** {@link BoundedPropagator} view of the instance. */
private class BoundedPropagatorView extends AbstractAnalyticalPropagator implements BoundedPropagator {
/** Min date. */
private final AbsoluteDate minDate;
/** Max date. */
private final AbsoluteDate maxDate;
/** Simple constructor.
* @param startDate start date of the propagation
* @param endDate end date of the propagation
*/
BoundedPropagatorView(final AbsoluteDate startDate, final AbsoluteDate endDate) {
super(AbstractAnalyticalPropagator.this.getAttitudeProvider());
if (startDate.compareTo(endDate) <= 0) {
minDate = startDate;
maxDate = endDate;
} else {
minDate = endDate;
maxDate = startDate;
}
try {
// copy the same additional state providers as the original propagator
for (AdditionalStateProvider provider : AbstractAnalyticalPropagator.this.getAdditionalStateProviders()) {
addAdditionalStateProvider(provider);
}
} catch (OrekitException oe) {
// as the providers are already compatible with each other,
// this should never happen
throw new OrekitInternalError(null);
}
}
/** {@inheritDoc} */
public AbsoluteDate getMinDate() {
return minDate;
}
/** {@inheritDoc} */
public AbsoluteDate getMaxDate() {
return maxDate;
}
/** {@inheritDoc} */
protected Orbit propagateOrbit(final AbsoluteDate target) {
return AbstractAnalyticalPropagator.this.propagateOrbit(target);
}
/** {@inheritDoc} */
public double getMass(final AbsoluteDate date) {
return AbstractAnalyticalPropagator.this.getMass(date);
}
/** {@inheritDoc} */
public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame) {
return propagate(date).getPVCoordinates(frame);
}
/** {@inheritDoc} */
public void resetInitialState(final SpacecraftState state) {
AbstractAnalyticalPropagator.this.resetInitialState(state);
}
/** {@inheritDoc} */
protected void resetIntermediateState(final SpacecraftState state, final boolean forward) {
AbstractAnalyticalPropagator.this.resetIntermediateState(state, forward);
}
/** {@inheritDoc} */
public SpacecraftState getInitialState() {
return AbstractAnalyticalPropagator.this.getInitialState();
}
/** {@inheritDoc} */
public Frame getFrame() {
return AbstractAnalyticalPropagator.this.getFrame();
}
}
/** Internal class for local propagation. */
private class BasicStepInterpolator implements OrekitStepInterpolator {
/** Previous state. */
private final SpacecraftState previousState;
/** Current state. */
private final SpacecraftState currentState;
/** Forward propagation indicator. */
private final boolean forward;
/** Simple constructor.
* @param isForward integration direction indicator
* @param previousState start of the step
* @param currentState end of the step
*/
BasicStepInterpolator(final boolean isForward,
final SpacecraftState previousState,
final SpacecraftState currentState) {
this.forward = isForward;
this.previousState = previousState;
this.currentState = currentState;
}
/** {@inheritDoc} */
@Override
public SpacecraftState getPreviousState() {
return previousState;
}
/** {@inheritDoc} */
@Override
public boolean isPreviousStateInterpolated() {
// no difference in analytical propagators
return false;
}
/** {@inheritDoc} */
@Override
public SpacecraftState getCurrentState() {
return currentState;
}
/** {@inheritDoc} */
@Override
public boolean isCurrentStateInterpolated() {
// no difference in analytical propagators
return false;
}
/** {@inheritDoc} */
@Override
public SpacecraftState getInterpolatedState(final AbsoluteDate date) {
// compute the basic spacecraft state
final SpacecraftState basicState = basicPropagate(date);
// add the additional states
return updateAdditionalStates(basicState);
}
/** {@inheritDoc} */
@Override
public boolean isForward() {
return forward;
}
/** {@inheritDoc} */
@Override
public BasicStepInterpolator restrictStep(final SpacecraftState newPreviousState,
final SpacecraftState newCurrentState) {
return new BasicStepInterpolator(forward, newPreviousState, newCurrentState);
}
}
}