EphemerisFile.java

  1. /* Contributed in the public domain.
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.files.general;

  19. import java.util.ArrayList;
  20. import java.util.List;
  21. import java.util.Map;

  23. import org.orekit.errors.OrekitException;
  24. import org.orekit.frames.Frame;
  25. import org.orekit.propagation.BoundedPropagator;
  26. import org.orekit.propagation.Propagator;
  27. import org.orekit.propagation.analytical.AggregateBoundedPropagator;
  28. import org.orekit.time.AbsoluteDate;
  29. import org.orekit.utils.CartesianDerivativesFilter;
  30. import org.orekit.utils.TimeStampedPVCoordinates;

  32. /**
  33.  * An interface for accessing the data stored in an ephemeris file and using the data to
  34.  * create a working {@link org.orekit.propagation.Propagator Propagator}.
  35.  *
  36.  * <p> An {@link EphemerisFile} consists of one or more satellites each with a unique ID
  37.  * within the file. The ephemeris for each satellite consists of one or more segments.
  38.  *
  39.  * <p> Some ephemeris file formats may supply additional information that is not available
  40.  * via this interface. In those cases it is recommended that the parser return a subclass
  41.  * of this interface to provide access to the additional information.
  42.  *
  43.  * @param <C> type of the Cartesian coordinates
  44.  * @param <S> type of the segment
  45.  * @author Evan Ward
  46.  * @see SatelliteEphemeris
  47.  * @see EphemerisSegment
  48.  */
  49. public interface EphemerisFile<C extends TimeStampedPVCoordinates,
  50.                                S extends EphemerisFile.EphemerisSegment<C>> {

  52.     /**
  53.      * Get the loaded ephemeris for each satellite in the file.
  54.      *
  55.      * @return a map from the satellite's ID to the information about that satellite
  56.      * contained in the file.
  57.      */
  58.     Map<String, ? extends SatelliteEphemeris<C, S>> getSatellites();

  60.     /**
  61.      * Contains the information about a single satellite from an {@link EphemerisFile}.
  62.      *
  63.      * <p> A satellite ephemeris consists of one or more {@link EphemerisSegment}s.
  64.      * Segments are typically used to split up an ephemeris at discontinuous events, such
  65.      * as a maneuver.
  66.      * @param <C> type of the Cartesian coordinates
  67.      * @param <S> type of the segment
  68.      * @author Evan Ward
  69.      * @see EphemerisFile
  70.      * @see EphemerisSegment
  71.      */
  72.     interface SatelliteEphemeris<C extends TimeStampedPVCoordinates,
  73.                                  S extends EphemerisSegment<C>> {

  75.         /**
  76.          * Get the satellite ID. The satellite ID is unique only within the same ephemeris
  77.          * file.
  78.          *
  79.          * @return the satellite's ID, never {@code null}.
  80.          */
  81.         String getId();

  83.         /**
  84.          * Get the standard gravitational parameter for the satellite.
  85.          *
  86.          * @return the gravitational parameter used in {@link #getPropagator()}, in m³/s².
  87.          */
  88.         double getMu();

  90.         /**
  91.          * Get the segments of the ephemeris.
  92.          *
  93.          * <p> Ephemeris segments are typically used to split an ephemeris around
  94.          * discontinuous events, such as maneuvers.
  95.          *
  96.          * @return the segments contained in the ephemeris file for this satellite.
  97.          */
  98.         List<S> getSegments();

  100.         /**
  101.          * Get the start date of the ephemeris.
  102.          *
  103.          * <p> The date returned by this method is equivalent to {@code
  104.          * getPropagator().getMinDate()}.
  105.          *
  106.          * @return ephemeris start date.
  107.          */
  108.         AbsoluteDate getStart();

  110.         /**
  111.          * Get the end date of the ephemeris.
  112.          *
  113.          * <p> The date returned by this method is equivalent to {@code getPropagator().getMaxDate()}.
  114.          *
  115.          * @return ephemeris end date.
  116.          */
  117.         AbsoluteDate getStop();

  119.         /**
  120.          * View this ephemeris as a propagator, combining data from all {@link
  121.          * #getSegments() segments}.
  122.          *
  123.          * <p>In order to view the ephemeris for this satellite as a {@link Propagator}
  124.          * several conditions must be met. An Orekit {@link Frame} must be constructable
  125.          * from the frame specification in the ephemeris file. This condition is met when
  126.          * {@link EphemerisSegment#getFrame()} return normally for all {@link
  127.          * #getSegments() segments}. If there are multiple segments they must be adjacent
  128.          * such that there are no duplicates or gaps in the ephemeris. The definition of
  129.          * adjacent depends on the ephemeris format as some formats define usable start
  130.          * and stop times that are different from the ephemeris data start and stop times.
  131.          * If these conditions are not met an {@link OrekitException} may be thrown by
  132.          * this method or by one of the methods of the returned {@link Propagator}.
  133.          *
  134.          * <p> Each call to this method creates a new propagator.
  135.          *
  136.          * @return a propagator for all the data in this ephemeris file.
  137.          */
  138.         default BoundedPropagator getPropagator() {
  139.             final List<BoundedPropagator> propagators = new ArrayList<>();
  140.             for (final EphemerisSegment<C> segment : this.getSegments()) {
  141.                 propagators.add(segment.getPropagator());
  142.             }
  143.             return new AggregateBoundedPropagator(propagators);
  144.         }

  146.     }

  148.     /**
  149.      * A segment of an ephemeris for a satellite.
  150.      *
  151.      * <p> Segments are typically used to split an ephemeris around discontinuous events
  152.      * such as maneuvers.
  153.      *
  154.      * @param <C> type of the Cartesian coordinates
  155.      * @author Evan Ward
  156.      * @see EphemerisFile
  157.      * @see SatelliteEphemeris
  158.      */
  159.     interface EphemerisSegment<C extends TimeStampedPVCoordinates> {

  161.         /**
  162.          * Get the standard gravitational parameter for the satellite.
  163.          *
  164.          * @return the gravitational parameter used in {@link #getPropagator()}, in m³/s².
  165.          */
  166.         double getMu();

  168.         /**
  169.          * Get the reference frame for this ephemeris segment. The defining frame for
  170.          * {@link #getCoordinates()}.
  171.          *
  172.          * @return the reference frame for this segment. Never {@code null}.
  173.          */
  174.         Frame getFrame();

  176.         /**
  177.          * Get the inertial reference frame for this ephemeris segment. Defines the
  178.          * propagation frame for {@link #getPropagator()}.
  179.          *
  180.          * <p>The default implementation returns {@link #getFrame()} if it is inertial.
  181.          * Otherwise it returns {@link Frame#getRoot()}. Implementors are encouraged to
  182.          * override this default implementation if a more suitable inertial frame is
  183.          * available.
  184.          *
  185.          * @return an reference frame that is inertial, i.e. {@link
  186.          * Frame#isPseudoInertial()} is {@code true}. May be the same as {@link
  187.          * #getFrame()} if it is inertial.
  188.          */
  189.         default Frame getInertialFrame() {
  190.             final Frame frame = getFrame();
  191.             if (frame.isPseudoInertial()) {
  192.                 return frame;
  193.             }
  194.             return Frame.getRoot();
  195.         }

  197.         /**
  198.          * Get the number of samples to use in interpolation.
  199.          *
  200.          * @return the number of points to use for interpolation.
  201.          */
  202.         int getInterpolationSamples();

  204.         /**
  205.          * Get which derivatives of position are available in this ephemeris segment.
  206.          *
  207.          * <p> While {@link #getCoordinates()} always returns position, velocity, and
  208.          * acceleration the return value from this method indicates which of those are in
  209.          * the ephemeris file and are actually valid.
  210.          *
  211.          * @return a value indicating if the file contains velocity and/or acceleration
  212.          * data.
  213.          */
  214.         CartesianDerivativesFilter getAvailableDerivatives();

  216.         /**
  217.          * Get the coordinates for this ephemeris segment in {@link #getFrame()}.
  218.          *
  219.          * @return a list of state vectors in chronological order. The coordinates are not
  220.          * necessarily evenly spaced in time. The value of {@link
  221.          * #getAvailableDerivatives()} indicates if the velocity or accelerations were
  222.          * specified in the file. Any position, velocity, or acceleration coordinates that
  223.          * are not specified in the ephemeris file are zero in the returned values.
  224.          */
  225.         List<C> getCoordinates();

  227.         /**
  228.          * Get the start date of this ephemeris segment.
  229.          *
  230.          * <p> The date returned by this method is equivalent to {@code
  231.          * getPropagator().getMinDate()}.
  232.          *
  233.          * @return ephemeris segment start date.
  234.          */
  235.         AbsoluteDate getStart();

  237.         /**
  238.          * Get the end date of this ephemeris segment.
  239.          *
  240.          * <p> The date returned by this method is equivalent to {@code
  241.          * getPropagator().getMaxDate()}.
  242.          *
  243.          * @return ephemeris segment end date.
  244.          */
  245.         AbsoluteDate getStop();

  247.         /**
  248.          * View this ephemeris segment as a propagator.
  249.          *
  250.          * <p>In order to view the ephemeris for this satellite as a {@link Propagator}
  251.          * several conditions must be met. An Orekit {@link Frame} must be constructable
  252.          * from the frame specification in the ephemeris file. This condition is met when
  253.          * {@link EphemerisSegment#getFrame()} return normally. Additionally,
  254.          * {@link #getMu()} must return a valid value. If these conditions are not met an
  255.          * {@link OrekitException} may be thrown by this method or by one of the methods
  256.          * of the returned {@link Propagator}.
  257.          *
  258.          * <p> Each call to this method creates a new propagator.
  259.          *
  260.          * @return a propagator for this ephemeris segment.
  261.          */
  262.         default BoundedPropagator getPropagator() {
  263.             return new EphemerisSegmentPropagator<>(this);
  264.         }

  266.     }

  268. }
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