InterSatDirectViewDetector.java
- /* Copyright 2002-2024 CS GROUP
- * Licensed to CS GROUP (CS) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * CS licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.orekit.propagation.events;
- import org.orekit.bodies.GeodeticPoint;
- import org.orekit.bodies.OneAxisEllipsoid;
- import org.orekit.frames.Frame;
- import org.orekit.propagation.PropagatorsParallelizer;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.propagation.events.handlers.ContinueOnEvent;
- import org.orekit.propagation.events.handlers.EventHandler;
- import org.orekit.time.AbsoluteDate;
- import org.orekit.utils.PVCoordinatesProvider;
- /** Detector for inter-satellites direct view (i.e. no masking by central body limb).
- * <p>
- * As this detector needs two satellites, it embeds one {@link
- * PVCoordinatesProvider coordinates provider} for the secondary satellite
- * and is registered as an event detector in the propagator of the primary
- * satellite. The secondary satellite provider will therefore be driven by this
- * detector (and hence by the propagator in which this detector is registered).
- * </p>
- * <p>
- * In order to avoid infinite recursion, care must be taken to have the secondary
- * satellite provider being <em>completely independent</em> from anything else.
- * In particular, if the provider is a propagator, it should <em>not</em> be run
- * together in a {@link PropagatorsParallelizer propagators parallelizer} with
- * the propagator this detector is registered in. It is fine however to configure
- * two separate propagators PsA and PsB with similar settings for the secondary satellite
- * and one propagator Pm for the primary satellite and then use Psa in this detector
- * registered within Pm while Pm and Psb are run in the context of a {@link
- * PropagatorsParallelizer propagators parallelizer}.
- * </p>
- * <p>
- * For efficiency reason during the event search loop, it is recommended to have
- * the secondary provider be an analytical propagator or an ephemeris. A numerical propagator
- * as a secondary propagator works but is expected to be computationally costly.
- * </p>
- * <p>
- * The {@code g} function of this detector is positive when satellites can see
- * each other directly and negative when the central body limb is in between and
- * blocks the direct view.
- * </p>
- * <p>
- * This detector only checks masking by central body limb, it does not take into
- * account satellites antenna patterns. If these patterns must be considered, then
- * this detector can be {@link BooleanDetector#andCombine(EventDetector...) and combined}
- * with the {@link BooleanDetector#notCombine(EventDetector) logical not} of
- * {@link FieldOfViewDetector field of view detectors}.
- * </p>
- * @author Luc Maisonobe
- * @since 9.3
- */
- public class InterSatDirectViewDetector extends AbstractDetector<InterSatDirectViewDetector> {
- /** Central body. */
- private final OneAxisEllipsoid body;
- /** Skimming altitude.
- * @since 12.0
- */
- private final double skimmingAltitude;
- /** Coordinates provider for the secondary satellite. */
- private final PVCoordinatesProvider secondary;
- /** simple constructor.
- *
- * @param body central body
- * @param secondary provider for the secondary satellite
- */
- public InterSatDirectViewDetector(final OneAxisEllipsoid body, final PVCoordinatesProvider secondary) {
- this(body, 0.0, secondary, s -> DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
- new ContinueOnEvent());
- }
- /** Private constructor.
- * @param body central body
- * @param skimmingAltitude skimming altitude at which events are triggered
- * @param secondary provider for the secondary satellite
- * @param maxCheck maximum checking interval
- * @param threshold convergence threshold (s)
- * @param maxIter maximum number of iterations in the event time search
- * @param handler event handler to call at event occurrences
- * @since 12.0
- */
- protected InterSatDirectViewDetector(final OneAxisEllipsoid body,
- final double skimmingAltitude,
- final PVCoordinatesProvider secondary,
- final AdaptableInterval maxCheck,
- final double threshold,
- final int maxIter,
- final EventHandler handler) {
- super(maxCheck, threshold, maxIter, handler);
- this.body = body;
- this.skimmingAltitude = skimmingAltitude;
- this.secondary = secondary;
- }
- /** Get the central body.
- * @return central body
- */
- public OneAxisEllipsoid getCentralBody() {
- return body;
- }
- /** Get the skimming altitude.
- * @return skimming altitude at which events are triggered
- * @since 12.0
- */
- public double getSkimmingAltitude() {
- return skimmingAltitude;
- }
- /** Get the provider for the secondary satellite.
- * @return provider for the secondary satellite
- */
- public PVCoordinatesProvider getSecondary() {
- return secondary;
- }
- /** {@inheritDoc} */
- @Override
- protected InterSatDirectViewDetector create(final AdaptableInterval newMaxCheck,
- final double newThreshold,
- final int newMaxIter,
- final EventHandler newHandler) {
- return new InterSatDirectViewDetector(body, skimmingAltitude, secondary,
- newMaxCheck, newThreshold, newMaxIter, newHandler);
- }
- /**
- * Setup the skimming altitude.
- * <p>
- * The skimming altitude is the lowest altitude of the path between satellites
- * at which events should be triggered. If set to 0.0, events are triggered
- * exactly when the path passes just at central body limb.
- * </p>
- * @param newSkimmingAltitude skimming altitude (m)
- * @return a new detector with updated configuration (the instance is not changed)
- * @see #getSkimmingAltitude()
- * @since 12.0
- */
- public InterSatDirectViewDetector withSkimmingAltitude(final double newSkimmingAltitude) {
- return new InterSatDirectViewDetector(body, newSkimmingAltitude, secondary,
- getMaxCheckInterval(), getThreshold(),
- getMaxIterationCount(), getHandler());
- }
- /** {@inheritDoc}
- * <p>
- * The {@code g} function of this detector is the difference between the minimum
- * altitude of intermediate points along the line of sight between satellites and the
- * {@link #getSkimmingAltitude() skimming altitude}. It is therefore positive when
- * all intermediate points are above the skimming altitude, meaning satellites can see
- * each other and it is negative when some intermediate points (which may be either
- * endpoints) dive below this altitude, meaning satellites cannot see each other.
- * </p>
- */
- @Override
- public double g(final SpacecraftState state) {
- // get the lowest point between primary and secondary
- final AbsoluteDate date = state.getDate();
- final Frame frame = body.getBodyFrame();
- final GeodeticPoint lowest = body.lowestAltitudeIntermediate(state.getPosition(frame),
- secondary.getPosition(date, frame));
- // compute switching function value as altitude difference
- return lowest.getAltitude() - skimmingAltitude;
- }
- }