IodLambert.java

  1. /* Copyright 2002-2025 CS GROUP
  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.estimation.iod;

  19. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  20. import org.hipparchus.geometry.euclidean.twod.Vector2D;
  21. import org.orekit.control.heuristics.lambert.LambertBoundaryConditions;
  22. import org.orekit.control.heuristics.lambert.LambertBoundaryVelocities;
  23. import org.orekit.control.heuristics.lambert.LambertSolver;
  24. import org.orekit.errors.OrekitException;
  25. import org.orekit.errors.OrekitMessages;
  26. import org.orekit.estimation.measurements.PV;
  27. import org.orekit.estimation.measurements.Position;
  28. import org.orekit.frames.Frame;
  29. import org.orekit.orbits.CartesianOrbit;
  30. import org.orekit.orbits.Orbit;
  31. import org.orekit.time.AbsoluteDate;
  32. import org.orekit.utils.TimeStampedPVCoordinates;

  34. /**
  35.  * Lambert position-based Initial Orbit Determination (IOD) algorithm, assuming Keplerian motion.
  36.  * <p>
  37.  * An orbit is determined from two position vectors.
  38.  * @author Joris Olympio
  39.  * @see LambertSolver
  40.  * @since 8.0
  41.  */
  42. public class IodLambert {

  44.     /** gravitational constant. */
  45.     private final double mu;

  47.     /** Creator.
  48.      *
  49.      * @param mu gravitational constant
  50.      */
  51.     public IodLambert(final double mu) {
  52.         this.mu = mu;
  53.     }

  55.     /** Estimate an initial orbit from two position measurements.
  56.      * <p>
  57.      * The logic for setting {@code posigrade} and {@code nRev} is that the
  58.      * sweep angle Δυ travelled by the object between {@code t1} and {@code t2} is
  59.      * 2π {@code nRev +1} - α if {@code posigrade} is false and 2π {@code nRev} + α
  60.      * if {@code posigrade} is true, where α is the separation angle between
  61.      * {@code p1} and {@code p2}, which is always computed between 0 and π
  62.      * (because in 3D without a normal reference, vector angles cannot go past π).
  63.      * </p>
  64.      * <p>
  65.      * This implies that {@code posigrade} should be set to true if {@code p2} is
  66.      * located in the half orbit starting at {@code p1} and it should be set to
  67.      * false if {@code p2} is located in the half orbit ending at {@code p1},
  68.      * regardless of the number of periods between {@code t1} and {@code t2},
  69.      * and {@code nRev} should be set accordingly.
  70.      * </p>
  71.      * <p>
  72.      * As an example, if {@code t2} is less than half a period after {@code t1},
  73.      * then {@code posigrade} should be {@code true} and {@code nRev} should be 0.
  74.      * If {@code t2} is more than half a period after {@code t1} but less than
  75.      * one period after {@code t1}, {@code posigrade} should be {@code false} and
  76.      * {@code nRev} should be 0.
  77.      * </p>
  78.      * @param frame     measurements frame
  79.      * @param posigrade flag indicating the direction of motion
  80.      * @param nRev      number of revolutions
  81.      * @param p1        first position measurement
  82.      * @param p2        second position measurement
  83.      * @return an initial Keplerian orbit estimation at the first observation date t1
  84.      * @since 11.0
  85.      */
  86.     public Orbit estimate(final Frame frame, final boolean posigrade,
  87.                           final int nRev, final Position p1,  final Position p2) {
  88.         return estimate(frame, posigrade, nRev,
  89.                         p1.getPosition(), p1.getDate(), p2.getPosition(), p2.getDate());
  90.     }

  92.     /** Estimate an initial orbit from two PV measurements.
  93.      * <p>
  94.      * The logic for setting {@code posigrade} and {@code nRev} is that the
  95.      * sweep angle Δυ travelled by the object between {@code t1} and {@code t2} is
  96.      * 2π {@code nRev +1} - α if {@code posigrade} is false and 2π {@code nRev} + α
  97.      * if {@code posigrade} is true, where α is the separation angle between
  98.      * {@code p1} and {@code p2}, which is always computed between 0 and π
  99.      * (because in 3D without a normal reference, vector angles cannot go past π).
  100.      * </p>
  101.      * <p>
  102.      * This implies that {@code posigrade} should be set to true if {@code p2} is
  103.      * located in the half orbit starting at {@code p1} and it should be set to
  104.      * false if {@code p2} is located in the half orbit ending at {@code p1},
  105.      * regardless of the number of periods between {@code t1} and {@code t2},
  106.      * and {@code nRev} should be set accordingly.
  107.      * </p>
  108.      * <p>
  109.      * As an example, if {@code t2} is less than half a period after {@code t1},
  110.      * then {@code posigrade} should be {@code true} and {@code nRev} should be 0.
  111.      * If {@code t2} is more than half a period after {@code t1} but less than
  112.      * one period after {@code t1}, {@code posigrade} should be {@code false} and
  113.      * {@code nRev} should be 0.
  114.      * </p>
  115.      * @param frame     measurements frame
  116.      * @param posigrade flag indicating the direction of motion
  117.      * @param nRev      number of revolutions
  118.      * @param pv1       first PV measurement
  119.      * @param pv2       second PV measurement
  120.      * @return an initial Keplerian orbit estimation at the first observation date t1
  121.      * @since 12.0
  122.      */
  123.     public Orbit estimate(final Frame frame, final boolean posigrade,
  124.                           final int nRev, final PV pv1,  final PV pv2) {
  125.         return estimate(frame, posigrade, nRev,
  126.                         pv1.getPosition(), pv1.getDate(), pv2.getPosition(), pv2.getDate());
  127.     }

  129.     /** Estimate a Keplerian orbit given two position vectors and a duration.
  130.      * <p>
  131.      * The logic for setting {@code posigrade} and {@code nRev} is that the
  132.      * sweep angle Δυ travelled by the object between {@code t1} and {@code t2} is
  133.      * 2π {@code nRev +1} - α if {@code posigrade} is false and 2π {@code nRev} + α
  134.      * if {@code posigrade} is true, where α is the separation angle between
  135.      * {@code p1} and {@code p2}, which is always computed between 0 and π
  136.      * (because in 3D without a normal reference, vector angles cannot go past π).
  137.      * </p>
  138.      * <p>
  139.      * This implies that {@code posigrade} should be set to true if {@code p2} is
  140.      * located in the half orbit starting at {@code p1} and it should be set to
  141.      * false if {@code p2} is located in the half orbit ending at {@code p1},
  142.      * regardless of the number of periods between {@code t1} and {@code t2},
  143.      * and {@code nRev} should be set accordingly.
  144.      * </p>
  145.      * <p>
  146.      * As an example, if {@code t2} is less than half a period after {@code t1},
  147.      * then {@code posigrade} should be {@code true} and {@code nRev} should be 0.
  148.      * If {@code t2} is more than half a period after {@code t1} but less than
  149.      * one period after {@code t1}, {@code posigrade} should be {@code false} and
  150.      * {@code nRev} should be 0.
  151.      * </p>
  152.      * @param frame     frame
  153.      * @param posigrade flag indicating the direction of motion
  154.      * @param nRev      number of revolutions
  155.      * @param p1        position vector 1
  156.      * @param t1        date of observation 1
  157.      * @param p2        position vector 2
  158.      * @param t2        date of observation 2
  159.      * @return  an initial Keplerian orbit estimate at the first observation date t1
  160.      */
  161.     public Orbit estimate(final Frame frame, final boolean posigrade,
  162.                           final int nRev,
  163.                           final Vector3D p1, final AbsoluteDate t1,
  164.                           final Vector3D p2, final AbsoluteDate t2) {
  165.         // Exception if t2 < t1
  166.         final double tau = t2.durationFrom(t1); // in seconds
  167.         if (tau < 0.) {
  168.             throw new OrekitException(OrekitMessages.NON_CHRONOLOGICAL_DATES_FOR_OBSERVATIONS, t1, t2, -tau);
  169.         }
  170.         final LambertSolver solver = new LambertSolver(mu);
  171.         final LambertBoundaryConditions boundaryConditions = new LambertBoundaryConditions(t1, p1, t2, p2,
  172.                 frame);
  173.         final LambertBoundaryVelocities velocities = solver.solve(posigrade, nRev, boundaryConditions);
  174.         if (velocities == null) {
  175.             return null;
  176.         } else {
  177.             return new CartesianOrbit(new TimeStampedPVCoordinates(t1, p1, velocities.getInitialVelocity()),
  178.                     frame, mu);
  179.         }
  180.     }

  182.     /** Lambert's solver for the historical, planar problem.
  183.      * Assume mu=1.
  184.      *
  185.      * @param r1 radius 1
  186.      * @param r2  radius 2
  187.      * @param dth sweep angle
  188.      * @param tau time of flight
  189.      * @param mRev number of revs
  190.      * @param V1 velocity at departure in (T, N) basis
  191.      * @return exit flag
  192.      * @deprecated as of 13.1, use {@link LambertSolver}
  193.      */
  194.     boolean solveLambertPb(final double r1, final double r2, final double dth, final double tau,
  195.                            final int mRev, final double[] V1) {
  196.         final Vector2D solution = LambertSolver.solveNormalized2D(r1, r2, dth, tau, mRev);
  197.         if (solution == Vector2D.NaN) {
  198.             return false;
  199.         } else {
  200.             V1[0] = solution.getX();
  201.             V1[1] = solution.getY();
  202.             return true;
  203.         }
  204.     }

  206. }
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