GroundStation.java

  1. /* Copyright 2002-2022 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.measurements;

  19. import java.util.Map;

  21. import org.hipparchus.Field;
  22. import org.hipparchus.analysis.differentiation.Gradient;
  23. import org.hipparchus.geometry.euclidean.threed.FieldRotation;
  24. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  25. import org.hipparchus.geometry.euclidean.threed.Rotation;
  26. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  27. import org.hipparchus.util.FastMath;
  28. import org.orekit.bodies.BodyShape;
  29. import org.orekit.bodies.FieldGeodeticPoint;
  30. import org.orekit.bodies.GeodeticPoint;
  31. import org.orekit.data.BodiesElements;
  32. import org.orekit.data.FundamentalNutationArguments;
  33. import org.orekit.errors.OrekitException;
  34. import org.orekit.errors.OrekitMessages;
  35. import org.orekit.frames.EOPHistory;
  36. import org.orekit.frames.FieldTransform;
  37. import org.orekit.frames.Frame;
  38. import org.orekit.frames.FramesFactory;
  39. import org.orekit.frames.StaticTransform;
  40. import org.orekit.frames.TopocentricFrame;
  41. import org.orekit.frames.Transform;
  42. import org.orekit.models.earth.displacement.StationDisplacement;
  43. import org.orekit.time.AbsoluteDate;
  44. import org.orekit.time.FieldAbsoluteDate;
  45. import org.orekit.time.UT1Scale;
  46. import org.orekit.utils.ParameterDriver;

  48. /** Class modeling a ground station that can perform some measurements.
  49.  * <p>
  50.  * This class adds a position offset parameter to a base {@link TopocentricFrame
  51.  * topocentric frame}.
  52.  * </p>
  53.  * <p>
  54.  * Since 9.0, this class also adds parameters for an additional polar motion
  55.  * and an additional prime meridian orientation. Since these parameters will
  56.  * have the same name for all ground stations, they will be managed consistently
  57.  * and allow to estimate Earth orientation precisely (this is needed for precise
  58.  * orbit determination). The polar motion and prime meridian orientation will
  59.  * be applied <em>after</em> regular Earth orientation parameters, so the value
  60.  * of the estimated parameters will be correction to EOP, they will not be the
  61.  * complete EOP values by themselves. Basically, this means that for Earth, the
  62.  * following transforms are applied in order, between inertial frame and ground
  63.  * station frame (for non-Earth based ground stations, different precession nutation
  64.  * models and associated planet oritentation parameters would be applied, if available):
  65.  * </p>
  66.  * <p>
  67.  * Since 9.3, this class also adds a station clock offset parameter, which manages
  68.  * the value that must be subtracted from the observed measurement date to get the real
  69.  * physical date at which the measurement was performed (i.e. the offset is negative
  70.  * if the ground station clock is slow and positive if it is fast).
  71.  * </p>
  72.  * <ol>
  73.  *   <li>precession/nutation, as theoretical model plus celestial pole EOP parameters</li>
  74.  *   <li>body rotation, as theoretical model plus prime meridian EOP parameters</li>
  75.  *   <li>polar motion, which is only from EOP parameters (no theoretical models)</li>
  76.  *   <li>additional body rotation, controlled by {@link #getPrimeMeridianOffsetDriver()} and {@link #getPrimeMeridianDriftDriver()}</li>
  77.  *   <li>additional polar motion, controlled by {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()},
  78.  *   {@link #getPolarOffsetYDriver()} and {@link #getPolarDriftYDriver()}</li>
  79.  *   <li>station clock offset, controlled by {@link #getClockOffsetDriver()}</li>
  80.  *   <li>station position offset, controlled by {@link #getEastOffsetDriver()},
  81.  *   {@link #getNorthOffsetDriver()} and {@link #getZenithOffsetDriver()}</li>
  82.  * </ol>
  83.  * @author Luc Maisonobe
  84.  * @since 8.0
  85.  */
  86. public class GroundStation {

  88.     /** Suffix for ground station position and clock offset parameters names. */
  89.     public static final String OFFSET_SUFFIX = "-offset";

  91.     /** Suffix for ground clock drift parameters name. */
  92.     public static final String DRIFT_SUFFIX = "-drift-clock";

  94.     /** Suffix for ground station intermediate frame name. */
  95.     public static final String INTERMEDIATE_SUFFIX = "-intermediate";

  97.     /** Clock offset scaling factor.
  98.      * <p>
  99.      * We use a power of 2 to avoid numeric noise introduction
  100.      * in the multiplications/divisions sequences.
  101.      * </p>
  102.      */
  103.     private static final double CLOCK_OFFSET_SCALE = FastMath.scalb(1.0, -10);

  105.     /** Position offsets scaling factor.
  106.      * <p>
  107.      * We use a power of 2 (in fact really 1.0 here) to avoid numeric noise introduction
  108.      * in the multiplications/divisions sequences.
  109.      * </p>
  110.      */
  111.     private static final double POSITION_OFFSET_SCALE = FastMath.scalb(1.0, 0);

  113.     /** Provider for Earth frame whose EOP parameters can be estimated. */
  114.     private final EstimatedEarthFrameProvider estimatedEarthFrameProvider;

  116.     /** Earth frame whose EOP parameters can be estimated. */
  117.     private final Frame estimatedEarthFrame;

  119.     /** Base frame associated with the station. */
  120.     private final TopocentricFrame baseFrame;

  122.     /** Fundamental nutation arguments. */
  123.     private final FundamentalNutationArguments arguments;

  125.     /** Displacement models. */
  126.     private final StationDisplacement[] displacements;

  128.     /** Driver for clock offset. */
  129.     private final ParameterDriver clockOffsetDriver;

  131.     /** Driver for clock drift. */
  132.     private final ParameterDriver clockDriftDriver;

  134.     /** Driver for position offset along the East axis. */
  135.     private final ParameterDriver eastOffsetDriver;

  137.     /** Driver for position offset along the North axis. */
  138.     private final ParameterDriver northOffsetDriver;

  140.     /** Driver for position offset along the zenith axis. */
  141.     private final ParameterDriver zenithOffsetDriver;

  143.     /** Build a ground station ignoring {@link StationDisplacement station displacements}.
  144.      * <p>
  145.      * The initial values for the pole and prime meridian parametric linear models
  146.      * ({@link #getPrimeMeridianOffsetDriver()}, {@link #getPrimeMeridianDriftDriver()},
  147.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()},
  148.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()}) are set to 0.
  149.      * The initial values for the station offset model ({@link #getClockOffsetDriver()},
  150.      * {@link #getEastOffsetDriver()}, {@link #getNorthOffsetDriver()},
  151.      * {@link #getZenithOffsetDriver()}) are set to 0.
  152.      * This implies that as long as these values are not changed, the offset frame is
  153.      * the same as the {@link #getBaseFrame() base frame}. As soon as some of these models
  154.      * are changed, the offset frame moves away from the {@link #getBaseFrame() base frame}.
  155.      * </p>
  156.      * @param baseFrame base frame associated with the station, without *any* parametric
  157.      * model (no station offset, no polar motion, no meridian shift)
  158.      * @see #GroundStation(TopocentricFrame, EOPHistory, StationDisplacement...)
  159.      */
  160.     public GroundStation(final TopocentricFrame baseFrame) {
  161.         this(baseFrame, FramesFactory.findEOP(baseFrame), new StationDisplacement[0]);
  162.     }

  164.     /** Simple constructor.
  165.      * <p>
  166.      * The initial values for the pole and prime meridian parametric linear models
  167.      * ({@link #getPrimeMeridianOffsetDriver()}, {@link #getPrimeMeridianDriftDriver()},
  168.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()},
  169.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()}) are set to 0.
  170.      * The initial values for the station offset model ({@link #getClockOffsetDriver()},
  171.      * {@link #getEastOffsetDriver()}, {@link #getNorthOffsetDriver()},
  172.      * {@link #getZenithOffsetDriver()}, {@link #getClockOffsetDriver()}) are set to 0.
  173.      * This implies that as long as these values are not changed, the offset frame is
  174.      * the same as the {@link #getBaseFrame() base frame}. As soon as some of these models
  175.      * are changed, the offset frame moves away from the {@link #getBaseFrame() base frame}.
  176.      * </p>
  177.      * @param baseFrame base frame associated with the station, without *any* parametric
  178.      * model (no station offset, no polar motion, no meridian shift)
  179.      * @param eopHistory EOP history associated with Earth frames
  180.      * @param displacements ground station displacement model (tides, ocean loading,
  181.      * atmospheric loading, thermal effects...)
  182.      * @since 9.1
  183.      */
  184.     public GroundStation(final TopocentricFrame baseFrame, final EOPHistory eopHistory,
  185.                          final StationDisplacement... displacements) {

  187.         this.baseFrame = baseFrame;

  189.         if (eopHistory == null) {
  190.             throw new OrekitException(OrekitMessages.NO_EARTH_ORIENTATION_PARAMETERS);
  191.         }

  193.         final UT1Scale baseUT1 = eopHistory.getTimeScales()
  194.                 .getUT1(eopHistory.getConventions(), eopHistory.isSimpleEop());
  195.         this.estimatedEarthFrameProvider = new EstimatedEarthFrameProvider(baseUT1);
  196.         this.estimatedEarthFrame = new Frame(baseFrame.getParent(), estimatedEarthFrameProvider,
  197.                                              baseFrame.getParent() + "-estimated");

  199.         if (displacements.length == 0) {
  200.             arguments = null;
  201.         } else {
  202.             arguments = eopHistory.getConventions().getNutationArguments(
  203.                     estimatedEarthFrameProvider.getEstimatedUT1(),
  204.                     eopHistory.getTimeScales());
  205.         }

  207.         this.displacements = displacements.clone();

  209.         this.clockOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-clock",
  210.                                                      0.0, CLOCK_OFFSET_SCALE,
  211.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  213.         this.clockDriftDriver = new ParameterDriver(baseFrame.getName() + DRIFT_SUFFIX,
  214.                                                     0.0, CLOCK_OFFSET_SCALE,
  215.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  217.         this.eastOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-East",
  218.                                                     0.0, POSITION_OFFSET_SCALE,
  219.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  221.         this.northOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-North",
  222.                                                      0.0, POSITION_OFFSET_SCALE,
  223.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  225.         this.zenithOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-Zenith",
  226.                                                       0.0, POSITION_OFFSET_SCALE,
  227.                                                       Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  229.     }

  231.     /** Get the displacement models.
  232.      * @return displacement models (empty if no model has been set up)
  233.      * @since 9.1
  234.      */
  235.     public StationDisplacement[] getDisplacements() {
  236.         return displacements.clone();
  237.     }

  239.     /** Get a driver allowing to change station clock (which is related to measurement date).
  240.      * @return driver for station clock offset
  241.      * @since 9.3
  242.      */
  243.     public ParameterDriver getClockOffsetDriver() {
  244.         return clockOffsetDriver;
  245.     }

  247.     /** Get a driver allowing to change station clock drift (which is related to measurement date).
  248.      * @return driver for station clock drift
  249.      * @since 10.3
  250.      */
  251.     public ParameterDriver getClockDriftDriver() {
  252.         return clockDriftDriver;
  253.     }

  255.     /** Get a driver allowing to change station position along East axis.
  256.      * @return driver for station position offset along East axis
  257.      */
  258.     public ParameterDriver getEastOffsetDriver() {
  259.         return eastOffsetDriver;
  260.     }

  262.     /** Get a driver allowing to change station position along North axis.
  263.      * @return driver for station position offset along North axis
  264.      */
  265.     public ParameterDriver getNorthOffsetDriver() {
  266.         return northOffsetDriver;
  267.     }

  269.     /** Get a driver allowing to change station position along Zenith axis.
  270.      * @return driver for station position offset along Zenith axis
  271.      */
  272.     public ParameterDriver getZenithOffsetDriver() {
  273.         return zenithOffsetDriver;
  274.     }

  276.     /** Get a driver allowing to add a prime meridian rotation.
  277.      * <p>
  278.      * The parameter is an angle in radians. In order to convert this
  279.      * value to a DUT1 in seconds, the value must be divided by
  280.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  281.      * of Earth from the TIRF model).
  282.      * </p>
  283.      * @return driver for prime meridian rotation
  284.      */
  285.     public ParameterDriver getPrimeMeridianOffsetDriver() {
  286.         return estimatedEarthFrameProvider.getPrimeMeridianOffsetDriver();
  287.     }

  289.     /** Get a driver allowing to add a prime meridian rotation rate.
  290.      * <p>
  291.      * The parameter is an angle rate in radians per second. In order to convert this
  292.      * value to a LOD in seconds, the value must be multiplied by -86400 and divided by
  293.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  294.      * of Earth from the TIRF model).
  295.      * </p>
  296.      * @return driver for prime meridian rotation rate
  297.      */
  298.     public ParameterDriver getPrimeMeridianDriftDriver() {
  299.         return estimatedEarthFrameProvider.getPrimeMeridianDriftDriver();
  300.     }

  302.     /** Get a driver allowing to add a polar offset along X.
  303.      * <p>
  304.      * The parameter is an angle in radians
  305.      * </p>
  306.      * @return driver for polar offset along X
  307.      */
  308.     public ParameterDriver getPolarOffsetXDriver() {
  309.         return estimatedEarthFrameProvider.getPolarOffsetXDriver();
  310.     }

  312.     /** Get a driver allowing to add a polar drift along X.
  313.      * <p>
  314.      * The parameter is an angle rate in radians per second
  315.      * </p>
  316.      * @return driver for polar drift along X
  317.      */
  318.     public ParameterDriver getPolarDriftXDriver() {
  319.         return estimatedEarthFrameProvider.getPolarDriftXDriver();
  320.     }

  322.     /** Get a driver allowing to add a polar offset along Y.
  323.      * <p>
  324.      * The parameter is an angle in radians
  325.      * </p>
  326.      * @return driver for polar offset along Y
  327.      */
  328.     public ParameterDriver getPolarOffsetYDriver() {
  329.         return estimatedEarthFrameProvider.getPolarOffsetYDriver();
  330.     }

  332.     /** Get a driver allowing to add a polar drift along Y.
  333.      * <p>
  334.      * The parameter is an angle rate in radians per second
  335.      * </p>
  336.      * @return driver for polar drift along Y
  337.      */
  338.     public ParameterDriver getPolarDriftYDriver() {
  339.         return estimatedEarthFrameProvider.getPolarDriftYDriver();
  340.     }

  342.     /** Get the base frame associated with the station.
  343.      * <p>
  344.      * The base frame corresponds to a null position offset, null
  345.      * polar motion, null meridian shift
  346.      * </p>
  347.      * @return base frame associated with the station
  348.      */
  349.     public TopocentricFrame getBaseFrame() {
  350.         return baseFrame;
  351.     }

  353.     /** Get the estimated Earth frame, including the estimated linear models for pole and prime meridian.
  354.      * <p>
  355.      * This frame is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  356.      * {@link #getPrimeMeridianDriftDriver() driver prime meridian drift},
  357.      * {@link #getPolarOffsetXDriver() driver for polar offset along X},
  358.      * {@link #getPolarDriftXDriver() driver for polar drift along X},
  359.      * {@link #getPolarOffsetYDriver() driver for polar offset along Y},
  360.      * {@link #getPolarDriftYDriver() driver for polar drift along Y}, so its orientation changes when
  361.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  362.      * </p>
  363.      * @return estimated Earth frame
  364.      * @since 9.1
  365.      */
  366.     public Frame getEstimatedEarthFrame() {
  367.         return estimatedEarthFrame;
  368.     }

  370.     /** Get the estimated UT1 scale, including the estimated linear models for prime meridian.
  371.      * <p>
  372.      * This time scale is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  373.      * and {@link #getPrimeMeridianDriftDriver() driver prime meridian drift}, so its offset from UTC changes when
  374.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  375.      * </p>
  376.      * @return estimated Earth frame
  377.      * @since 9.1
  378.      */
  379.     public UT1Scale getEstimatedUT1() {
  380.         return estimatedEarthFrameProvider.getEstimatedUT1();
  381.     }

  383.     /** Get the station displacement.
  384.      * @param date current date
  385.      * @param position raw position of the station in Earth frame
  386.      * before displacement is applied
  387.      * @return station displacement
  388.      * @since 9.1
  389.      */
  390.     private Vector3D computeDisplacement(final AbsoluteDate date, final Vector3D position) {
  391.         Vector3D displacement = Vector3D.ZERO;
  392.         if (arguments != null) {
  393.             final BodiesElements elements = arguments.evaluateAll(date);
  394.             for (final StationDisplacement sd : displacements) {
  395.                 // we consider all displacements apply to the same initial position,
  396.                 // i.e. they apply simultaneously, not according to some order
  397.                 displacement = displacement.add(sd.displacement(elements, estimatedEarthFrame, position));
  398.             }
  399.         }
  400.         return displacement;
  401.     }

  403.     /** Get the geodetic point at the center of the offset frame.
  404.      * @param date current date (may be null if displacements are ignored)
  405.      * @return geodetic point at the center of the offset frame
  406.      * @since 9.1
  407.      */
  408.     public GeodeticPoint getOffsetGeodeticPoint(final AbsoluteDate date) {

  410.         // take station offset into account
  411.         final double    x          = eastOffsetDriver.getValue();
  412.         final double    y          = northOffsetDriver.getValue();
  413.         final double    z          = zenithOffsetDriver.getValue();
  414.         final BodyShape baseShape  = baseFrame.getParentShape();
  415.         final StaticTransform baseToBody =
  416.                 baseFrame.getStaticTransformTo(baseShape.getBodyFrame(), date);
  417.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));

  419.         if (date != null) {
  420.             origin = origin.add(computeDisplacement(date, origin));
  421.         }

  423.         return baseShape.transform(origin, baseShape.getBodyFrame(), null);

  425.     }

  427.     /** Get the transform between offset frame and inertial frame.
  428.      * <p>
  429.      * The offset frame takes the <em>current</em> position offset,
  430.      * polar motion and the meridian shift into account. The frame
  431.      * returned is disconnected from later changes in the parameters.
  432.      * When the {@link ParameterDriver parameters} managing these
  433.      * offsets are changed, the method must be called again to retrieve
  434.      * a new offset frame.
  435.      * </p>
  436.      * @param inertial inertial frame to transform to
  437.      * @param clockDate date of the transform as read by the ground station clock (i.e. clock offset <em>not</em> compensated)
  438.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  439.      * date (i.e. with clock, Earth and station offsets applied)
  440.      */
  441.     public Transform getOffsetToInertial(final Frame inertial, final AbsoluteDate clockDate) {

  443.         // take clock offset into account
  444.         final double offset = clockOffsetDriver.getValue();
  445.         final AbsoluteDate offsetCompensatedDate = new AbsoluteDate(clockDate, -offset);

  447.         // take Earth offsets into account
  448.         final Transform intermediateToBody = estimatedEarthFrameProvider.getTransform(offsetCompensatedDate).getInverse();

  450.         // take station offsets into account
  451.         final double    x          = eastOffsetDriver.getValue();
  452.         final double    y          = northOffsetDriver.getValue();
  453.         final double    z          = zenithOffsetDriver.getValue();
  454.         final BodyShape baseShape  = baseFrame.getParentShape();
  455.         final StaticTransform baseToBody = baseFrame
  456.                 .getStaticTransformTo(baseShape.getBodyFrame(), offsetCompensatedDate);
  457.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));
  458.         origin = origin.add(computeDisplacement(offsetCompensatedDate, origin));

  460.         final GeodeticPoint originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  461.         final Transform offsetToIntermediate =
  462.                         new Transform(offsetCompensatedDate,
  463.                                       new Transform(offsetCompensatedDate,
  464.                                                     new Rotation(Vector3D.PLUS_I, Vector3D.PLUS_K,
  465.                                                                  originGP.getEast(), originGP.getZenith()),
  466.                                                     Vector3D.ZERO),
  467.                                       new Transform(offsetCompensatedDate, origin));

  469.         // combine all transforms together
  470.         final Transform bodyToInert        = baseFrame.getParent().getTransformTo(inertial, offsetCompensatedDate);

  472.         return new Transform(offsetCompensatedDate, offsetToIntermediate, new Transform(offsetCompensatedDate, intermediateToBody, bodyToInert));

  474.     }

  476.     /** Get the transform between offset frame and inertial frame with derivatives.
  477.      * <p>
  478.      * As the East and North vectors are not well defined at pole, the derivatives
  479.      * of these two vectors diverge to infinity as we get closer to the pole.
  480.      * So this method should not be used for stations less than 0.0001 degree from
  481.      * either poles.
  482.      * </p>
  483.      * @param inertial inertial frame to transform to
  484.      * @param clockDate date of the transform as read by the ground station clock (i.e. clock offset <em>not</em> compensated)
  485.      * @param freeParameters total number of free parameters in the gradient
  486.      * @param indices indices of the estimated parameters in derivatives computations
  487.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  488.      * date (i.e. with clock, Earth and station offsets applied)
  489.      * @see #getOffsetToInertial(Frame, FieldAbsoluteDate, int, Map)
  490.      * @since 10.2
  491.      */
  492.     public FieldTransform<Gradient> getOffsetToInertial(final Frame inertial,
  493.                                                         final AbsoluteDate clockDate,
  494.                                                         final int freeParameters,
  495.                                                         final Map<String, Integer> indices) {
  496.         // take clock offset into account
  497.         final Gradient offset = clockOffsetDriver.getValue(freeParameters, indices);
  498.         final FieldAbsoluteDate<Gradient> offsetCompensatedDate =
  499.                         new FieldAbsoluteDate<>(clockDate, offset.negate());

  501.         return getOffsetToInertial(inertial, offsetCompensatedDate, freeParameters, indices);
  502.     }

  504.     /** Get the transform between offset frame and inertial frame with derivatives.
  505.      * <p>
  506.      * As the East and North vectors are not well defined at pole, the derivatives
  507.      * of these two vectors diverge to infinity as we get closer to the pole.
  508.      * So this method should not be used for stations less than 0.0001 degree from
  509.      * either poles.
  510.      * </p>
  511.      * @param inertial inertial frame to transform to
  512.      * @param offsetCompensatedDate date of the transform, clock offset and its derivatives already compensated
  513.      * @param freeParameters total number of free parameters in the gradient
  514.      * @param indices indices of the estimated parameters in derivatives computations
  515.      * @return transform between offset frame and inertial frame, at specified date
  516.      * @since 10.2
  517.      */
  518.     public FieldTransform<Gradient> getOffsetToInertial(final Frame inertial,
  519.                                                         final FieldAbsoluteDate<Gradient> offsetCompensatedDate,
  520.                                                         final int freeParameters,
  521.                                                         final Map<String, Integer> indices) {

  523.         final Field<Gradient>         field = offsetCompensatedDate.getField();
  524.         final FieldVector3D<Gradient> zero  = FieldVector3D.getZero(field);
  525.         final FieldVector3D<Gradient> plusI = FieldVector3D.getPlusI(field);
  526.         final FieldVector3D<Gradient> plusK = FieldVector3D.getPlusK(field);

  528.         // take Earth offsets into account
  529.         final FieldTransform<Gradient> intermediateToBody =
  530.                         estimatedEarthFrameProvider.getTransform(offsetCompensatedDate, freeParameters, indices).getInverse();

  532.         // take station offsets into account
  533.         final Gradient  x          = eastOffsetDriver.getValue(freeParameters, indices);
  534.         final Gradient  y          = northOffsetDriver.getValue(freeParameters, indices);
  535.         final Gradient  z          = zenithOffsetDriver.getValue(freeParameters, indices);
  536.         final BodyShape            baseShape  = baseFrame.getParentShape();
  537.         final StaticTransform      baseToBody = baseFrame
  538.                 .getStaticTransformTo(baseShape.getBodyFrame(), null);

  540.         FieldVector3D<Gradient> origin = baseToBody.transformPosition(new FieldVector3D<>(x, y, z));
  541.         origin = origin.add(computeDisplacement(offsetCompensatedDate.toAbsoluteDate(), origin.toVector3D()));
  542.         final FieldGeodeticPoint<Gradient> originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  543.         final FieldTransform<Gradient> offsetToIntermediate =
  544.                         new FieldTransform<>(offsetCompensatedDate,
  545.                                              new FieldTransform<>(offsetCompensatedDate,
  546.                                                                   new FieldRotation<>(plusI, plusK,
  547.                                                                                       originGP.getEast(), originGP.getZenith()),
  548.                                                                   zero),
  549.                                              new FieldTransform<>(offsetCompensatedDate, origin));

  551.         // combine all transforms together
  552.         final FieldTransform<Gradient> bodyToInert = baseFrame.getParent().getTransformTo(inertial, offsetCompensatedDate);

  554.         return new FieldTransform<>(offsetCompensatedDate,
  555.                                     offsetToIntermediate,
  556.                                     new FieldTransform<>(offsetCompensatedDate, intermediateToBody, bodyToInert));

  558.     }

  560. }
Created with JaCoCo 0.8.8.202204050719