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.time.TimeScale;
  30. import org.orekit.utils.CartesianDerivativesFilter;
  31. import org.orekit.utils.TimeStampedPVCoordinates;

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

  50.     /**
  51.      * Get the loaded ephemeris for each satellite in the file.
  52.      *
  53.      * @return a map from the satellite's ID to the information about that satellite
  54.      * contained in the file.
  55.      */
  56.     Map<String, ? extends SatelliteEphemeris> getSatellites();

  58.     /**
  59.      * Contains the information about a single satellite from an {@link EphemerisFile}.
  60.      *
  61.      * <p> A satellite ephemeris consists of one or more {@link EphemerisSegment}s.
  62.      * Segments are typically used to split up an ephemeris at discontinuous events, such
  63.      * as a maneuver.
  64.      *
  65.      * @author Evan Ward
  66.      * @see EphemerisFile
  67.      * @see EphemerisSegment
  68.      */
  69.     interface SatelliteEphemeris {

  71.         /**
  72.          * Get the satellite ID. The satellite ID is unique only within the same ephemeris
  73.          * file.
  74.          *
  75.          * @return the satellite's ID, never {@code null}.
  76.          */
  77.         String getId();

  79.         /**
  80.          * Get the standard gravitational parameter for the satellite.
  81.          *
  82.          * @return the gravitational parameter use in {@link #getPropagator()}, in m^3 /
  83.          * s^2.
  84.          */
  85.         double getMu();

  87.         /**
  88.          * Get the segments of the ephemeris.
  89.          *
  90.          * <p> Ephemeris segments are typically used to split an ephemeris around
  91.          * discontinuous events, such as maneuvers.
  92.          *
  93.          * @return the segments contained in the ephemeris file for this satellite.
  94.          */
  95.         List<? extends EphemerisSegment> getSegments();

  97.         /**
  98.          * Get the start date of the ephemeris.
  99.          *
  100.          * <p> The date returned by this method is equivalent to {@code
  101.          * getPropagator().getMinDate()}.
  102.          *
  103.          * @return ephemeris start date.
  104.          */
  105.         AbsoluteDate getStart();

  107.         /**
  108.          * Get the end date of the ephemeris.
  109.          *
  110.          * <p> The date returned by this method is equivalent to {@code
  111.          * getPropagator().getMaxDate()}.
  112.          *
  113.          * @return ephemeris end date.
  114.          */
  115.         AbsoluteDate getStop();

  117.         /**
  118.          * View this ephemeris as a propagator, combining data from all {@link
  119.          * #getSegments() segments}.
  120.          *
  121.          * <p>In order to view the ephemeris for this satellite as a {@link Propagator}
  122.          * several conditions must be met. An Orekit {@link Frame} and {@link TimeScale}
  123.          * must be constructable from the frame and time scale specification in the
  124.          * ephemeris file. This condition is met when {@link EphemerisSegment#getFrame()}
  125.          * and {@link EphemerisSegment#getTimeScale()} return normally for all {@link
  126.          * #getSegments() segments}. If there are multiple segments they must be adjacent
  127.          * such that there are no duplicates or gaps in the ephemeris. The definition of
  128.          * adjacent depends on the ephemeris format as some formats define usable start
  129.          * and stop times that are different from the ephemeris data start and stop times.
  130.          * If these conditions are not met an {@link OrekitException} may be thrown by
  131.          * this method or by one of the methods of the returned {@link Propagator}.
  132.          *
  133.          * <p> Each call to this method creates a new propagator.
  134.          *
  135.          * @return a propagator for all the data in this ephemeris file.
  136.          */
  137.         default BoundedPropagator getPropagator() {
  138.             final List<BoundedPropagator> propagators = new ArrayList<>();
  139.             for (final EphemerisSegment segment : this.getSegments()) {
  140.                 propagators.add(segment.getPropagator());
  141.             }
  142.             return new AggregateBoundedPropagator(propagators);
  143.         }

  145.     }

  147.     /**
  148.      * A segment of an ephemeris for a satellite.
  149.      *
  150.      * <p> Segments are typically used to split an ephemeris around discontinuous events
  151.      * such as maneuvers.
  152.      *
  153.      * @author Evan Ward
  154.      * @see EphemerisFile
  155.      * @see SatelliteEphemeris
  156.      */
  157.     interface EphemerisSegment {

  159.         /**
  160.          * Get the standard gravitational parameter for the satellite.
  161.          *
  162.          * @return the gravitational parameter use in {@link #getPropagator()}, in m^3 /
  163.          * s^2.
  164.          */
  165.         double getMu();

  167.         /**
  168.          * Get the name of the center of the coordinate system the ephemeris is provided
  169.          * in. This may be a natural origin, such as the center of the Earth, another
  170.          * satellite, etc.
  171.          *
  172.          * @return the name of the frame center
  173.          */
  174.         String getFrameCenterString();

  176.         /**
  177.          * Get the defining frame for this ephemeris segment.
  178.          *
  179.          * @return the frame identifier, as specified in the ephemeris file, or {@code
  180.          * null} if the ephemeris file does not specify a frame.
  181.          */
  182.         String getFrameString();

  184.         /**
  185.          * Get the reference frame for this ephemeris segment. The defining frame for
  186.          * {@link #getCoordinates()}.
  187.          *
  188.          * @return the reference frame for this segment. Never {@code null}.
  189.          */
  190.         Frame getFrame();

  192.         /**
  193.          * Get the inertial reference frame for this ephemeris segment. Defines the
  194.          * propagation frame for {@link #getPropagator()}.
  195.          *
  196.          * <p>The default implementation returns {@link #getFrame()} if it is inertial.
  197.          * Otherwise it returns {@link Frame#getRoot()}. Implementors are encouraged to
  198.          * override this default implementation if a more suitable inertial frame is
  199.          * available.
  200.          *
  201.          * @return an reference frame that is inertial, i.e. {@link
  202.          * Frame#isPseudoInertial()} is {@code true}. May be the same as {@link
  203.          * #getFrame()} if it is inertial.
  204.          */
  205.         default Frame getInertialFrame() {
  206.             final Frame frame = getFrame();
  207.             if (frame.isPseudoInertial()) {
  208.                 return frame;
  209.             }
  210.             return Frame.getRoot();
  211.         }

  213.         /**
  214.          * Get the time scale for this ephemeris segment.
  215.          *
  216.          * @return the time scale identifier, as specified in the ephemeris file, or
  217.          * {@code null} if the ephemeris file does not specify a time scale.
  218.          */
  219.         String getTimeScaleString();

  221.         /**
  222.          * Get the time scale for this ephemeris segment.
  223.          *
  224.          * @return the time scale for this segment. Never {@code null}.
  225.          */
  226.         TimeScale getTimeScale();

  228.         /**
  229.          * Get the number of samples to use in interpolation.
  230.          *
  231.          * @return the number of points to use for interpolation.
  232.          */
  233.         int getInterpolationSamples();

  235.         /**
  236.          * Get which derivatives of position are available in this ephemeris segment.
  237.          *
  238.          * <p> While {@link #getCoordinates()} always returns position, velocity, and
  239.          * acceleration the return value from this method indicates which of those are in
  240.          * the ephemeris file and are actually valid.
  241.          *
  242.          * @return a value indicating if the file contains velocity and/or acceleration
  243.          * data.
  244.          */
  245.         CartesianDerivativesFilter getAvailableDerivatives();

  247.         /**
  248.          * Get the coordinates for this ephemeris segment in {@link #getFrame()}.
  249.          *
  250.          * @return a list of state vectors in chronological order. The coordinates are not
  251.          * necessarily evenly spaced in time. The value of {@link
  252.          * #getAvailableDerivatives()} indicates if the velocity or accelerations were
  253.          * specified in the file. Any position, velocity, or acceleration coordinates that
  254.          * are not specified in the ephemeris file are zero in the returned values.
  255.          */
  256.         List<? extends TimeStampedPVCoordinates> getCoordinates();

  258.         /**
  259.          * Get the start date of this ephemeris segment.
  260.          *
  261.          * <p> The date returned by this method is equivalent to {@code
  262.          * getPropagator().getMinDate()}.
  263.          *
  264.          * @return ephemeris segment start date.
  265.          */
  266.         AbsoluteDate getStart();

  268.         /**
  269.          * Get the end date of this ephemeris segment.
  270.          *
  271.          * <p> The date returned by this method is equivalent to {@code
  272.          * getPropagator().getMaxDate()}.
  273.          *
  274.          * @return ephemeris segment end date.
  275.          */
  276.         AbsoluteDate getStop();

  278.         /**
  279.          * View this ephemeris segment as a propagator.
  280.          *
  281.          * <p>In order to view the ephemeris for this satellite as a {@link Propagator}
  282.          * several conditions must be met. An Orekit {@link Frame} and {@link TimeScale}
  283.          * must be constructable from the frame and time scale specification in the
  284.          * ephemeris file. This condition is met when {@link EphemerisSegment#getFrame()}
  285.          * and {@link EphemerisSegment#getTimeScale()} return normally. Additionally,
  286.          * {@link #getMu()} must return a valid value. If these conditions are not met an
  287.          * {@link OrekitException} may be thrown by this method or by one of the methods
  288.          * of the returned {@link Propagator}.
  289.          *
  290.          * <p> Each call to this method creates a new propagator.
  291.          *
  292.          * @return a propagator for this ephemeris segment.
  293.          */
  294.         default BoundedPropagator getPropagator() {
  295.             return new EphemerisSegmentPropagator(this);
  296.         }

  298.     }

  300. }
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