GroundStation.java

  1. /* Copyright 2002-2020 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.DSFactory;
  23. import org.hipparchus.analysis.differentiation.DerivativeStructure;
  24. import org.hipparchus.geometry.euclidean.threed.FieldRotation;
  25. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  26. import org.hipparchus.geometry.euclidean.threed.Rotation;
  27. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  28. import org.hipparchus.util.FastMath;
  29. import org.orekit.bodies.BodyShape;
  30. import org.orekit.bodies.FieldGeodeticPoint;
  31. import org.orekit.bodies.GeodeticPoint;
  32. import org.orekit.data.BodiesElements;
  33. import org.orekit.data.FundamentalNutationArguments;
  34. import org.orekit.errors.OrekitException;
  35. import org.orekit.errors.OrekitMessages;
  36. import org.orekit.frames.EOPHistory;
  37. import org.orekit.frames.FieldTransform;
  38. import org.orekit.frames.Frame;
  39. import org.orekit.frames.FramesFactory;
  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 station intermediate frame name. */
  92.     public static final String INTERMEDIATE_SUFFIX = "-intermediate";

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

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

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

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

  116.     /** Base frame associated with the station. */
  117.     private final TopocentricFrame baseFrame;

  119.     /** Fundamental nutation arguments. */
  120.     private final FundamentalNutationArguments arguments;

  122.     /** Displacement models. */
  123.     private final StationDisplacement[] displacements;

  125.     /** Driver for clock offset. */
  126.     private final ParameterDriver clockOffsetDriver;

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

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

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

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

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

  181.         this.baseFrame = baseFrame;

  183.         if (eopHistory == null) {
  184.             throw new OrekitException(OrekitMessages.NO_EARTH_ORIENTATION_PARAMETERS);
  185.         }

  187.         final UT1Scale baseUT1 = eopHistory.getTimeScales()
  188.                 .getUT1(eopHistory.getConventions(), eopHistory.isSimpleEop());
  189.         this.estimatedEarthFrameProvider = new EstimatedEarthFrameProvider(baseUT1);
  190.         this.estimatedEarthFrame = new Frame(baseFrame.getParent(), estimatedEarthFrameProvider,
  191.                                              baseFrame.getParent() + "-estimated");

  193.         if (displacements.length == 0) {
  194.             arguments = null;
  195.         } else {
  196.             arguments = eopHistory.getConventions().getNutationArguments(
  197.                     estimatedEarthFrameProvider.getEstimatedUT1(),
  198.                     eopHistory.getTimeScales());
  199.         }

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

  203.         this.clockOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-clock",
  204.                                                      0.0, CLOCK_OFFSET_SCALE,
  205.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  207.         this.eastOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-East",
  208.                                                     0.0, POSITION_OFFSET_SCALE,
  209.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  211.         this.northOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-North",
  212.                                                      0.0, POSITION_OFFSET_SCALE,
  213.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  215.         this.zenithOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-Zenith",
  216.                                                       0.0, POSITION_OFFSET_SCALE,
  217.                                                       Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  219.     }

  221.     /** Get the displacement models.
  222.      * @return displacement models (empty if no model has been set up)
  223.      * @since 9.1
  224.      */
  225.     public StationDisplacement[] getDisplacements() {
  226.         return displacements.clone();
  227.     }

  229.     /** Get a driver allowing to change station clock (which is related to measurement date).
  230.      * @return driver for station clock offset
  231.      * @since 9.3
  232.      */
  233.     public ParameterDriver getClockOffsetDriver() {
  234.         return clockOffsetDriver;
  235.     }

  237.     /** Get a driver allowing to change station position along East axis.
  238.      * @return driver for station position offset along East axis
  239.      */
  240.     public ParameterDriver getEastOffsetDriver() {
  241.         return eastOffsetDriver;
  242.     }

  244.     /** Get a driver allowing to change station position along North axis.
  245.      * @return driver for station position offset along North axis
  246.      */
  247.     public ParameterDriver getNorthOffsetDriver() {
  248.         return northOffsetDriver;
  249.     }

  251.     /** Get a driver allowing to change station position along Zenith axis.
  252.      * @return driver for station position offset along Zenith axis
  253.      */
  254.     public ParameterDriver getZenithOffsetDriver() {
  255.         return zenithOffsetDriver;
  256.     }

  258.     /** Get a driver allowing to add a prime meridian rotation.
  259.      * <p>
  260.      * The parameter is an angle in radians. In order to convert this
  261.      * value to a DUT1 in seconds, the value must be divided by
  262.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  263.      * of Earth from the TIRF model).
  264.      * </p>
  265.      * @return driver for prime meridian rotation
  266.      */
  267.     public ParameterDriver getPrimeMeridianOffsetDriver() {
  268.         return estimatedEarthFrameProvider.getPrimeMeridianOffsetDriver();
  269.     }

  271.     /** Get a driver allowing to add a prime meridian rotation rate.
  272.      * <p>
  273.      * The parameter is an angle rate in radians per second. In order to convert this
  274.      * value to a LOD in seconds, the value must be multiplied by -86400 and divided by
  275.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  276.      * of Earth from the TIRF model).
  277.      * </p>
  278.      * @return driver for prime meridian rotation rate
  279.      */
  280.     public ParameterDriver getPrimeMeridianDriftDriver() {
  281.         return estimatedEarthFrameProvider.getPrimeMeridianDriftDriver();
  282.     }

  284.     /** Get a driver allowing to add a polar offset along X.
  285.      * <p>
  286.      * The parameter is an angle in radians
  287.      * </p>
  288.      * @return driver for polar offset along X
  289.      */
  290.     public ParameterDriver getPolarOffsetXDriver() {
  291.         return estimatedEarthFrameProvider.getPolarOffsetXDriver();
  292.     }

  294.     /** Get a driver allowing to add a polar drift along X.
  295.      * <p>
  296.      * The parameter is an angle rate in radians per second
  297.      * </p>
  298.      * @return driver for polar drift along X
  299.      */
  300.     public ParameterDriver getPolarDriftXDriver() {
  301.         return estimatedEarthFrameProvider.getPolarDriftXDriver();
  302.     }

  304.     /** Get a driver allowing to add a polar offset along Y.
  305.      * <p>
  306.      * The parameter is an angle in radians
  307.      * </p>
  308.      * @return driver for polar offset along Y
  309.      */
  310.     public ParameterDriver getPolarOffsetYDriver() {
  311.         return estimatedEarthFrameProvider.getPolarOffsetYDriver();
  312.     }

  314.     /** Get a driver allowing to add a polar drift along Y.
  315.      * <p>
  316.      * The parameter is an angle rate in radians per second
  317.      * </p>
  318.      * @return driver for polar drift along Y
  319.      */
  320.     public ParameterDriver getPolarDriftYDriver() {
  321.         return estimatedEarthFrameProvider.getPolarDriftYDriver();
  322.     }

  324.     /** Get the base frame associated with the station.
  325.      * <p>
  326.      * The base frame corresponds to a null position offset, null
  327.      * polar motion, null meridian shift
  328.      * </p>
  329.      * @return base frame associated with the station
  330.      */
  331.     public TopocentricFrame getBaseFrame() {
  332.         return baseFrame;
  333.     }

  335.     /** Get the estimated Earth frame, including the estimated linear models for pole and prime meridian.
  336.      * <p>
  337.      * This frame is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  338.      * {@link #getPrimeMeridianDriftDriver() driver prime meridian drift},
  339.      * {@link #getPolarOffsetXDriver() driver for polar offset along X},
  340.      * {@link #getPolarDriftXDriver() driver for polar drift along X},
  341.      * {@link #getPolarOffsetYDriver() driver for polar offset along Y},
  342.      * {@link #getPolarDriftYDriver() driver for polar drift along Y}, so its orientation changes when
  343.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  344.      * </p>
  345.      * @return estimated Earth frame
  346.      * @since 9.1
  347.      */
  348.     public Frame getEstimatedEarthFrame() {
  349.         return estimatedEarthFrame;
  350.     }

  352.     /** Get the estimated UT1 scale, including the estimated linear models for prime meridian.
  353.      * <p>
  354.      * This time scale is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  355.      * and {@link #getPrimeMeridianDriftDriver() driver prime meridian drift}, so its offset from UTC changes when
  356.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  357.      * </p>
  358.      * @return estimated Earth frame
  359.      * @since 9.1
  360.      */
  361.     public UT1Scale getEstimatedUT1() {
  362.         return estimatedEarthFrameProvider.getEstimatedUT1();
  363.     }

  365.     /** Get the station displacement.
  366.      * @param date current date
  367.      * @param position raw position of the station in Earth frame
  368.      * before displacement is applied
  369.      * @return station displacement
  370.      * @since 9.1
  371.      */
  372.     private Vector3D computeDisplacement(final AbsoluteDate date, final Vector3D position) {
  373.         Vector3D displacement = Vector3D.ZERO;
  374.         if (arguments != null) {
  375.             final BodiesElements elements = arguments.evaluateAll(date);
  376.             for (final StationDisplacement sd : displacements) {
  377.                 // we consider all displacements apply to the same initial position,
  378.                 // i.e. they apply simultaneously, not according to some order
  379.                 displacement = displacement.add(sd.displacement(elements, estimatedEarthFrame, position));
  380.             }
  381.         }
  382.         return displacement;
  383.     }

  385.     /** Get the geodetic point at the center of the offset frame.
  386.      * @param date current date (may be null if displacements are ignored)
  387.      * @return geodetic point at the center of the offset frame
  388.      * @since 9.1
  389.      */
  390.     public GeodeticPoint getOffsetGeodeticPoint(final AbsoluteDate date) {

  392.         // take station offset into account
  393.         final double    x          = eastOffsetDriver.getValue();
  394.         final double    y          = northOffsetDriver.getValue();
  395.         final double    z          = zenithOffsetDriver.getValue();
  396.         final BodyShape baseShape  = baseFrame.getParentShape();
  397.         final Transform baseToBody = baseFrame.getTransformTo(baseShape.getBodyFrame(), date);
  398.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));

  400.         if (date != null) {
  401.             origin = origin.add(computeDisplacement(date, origin));
  402.         }

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

  406.     }

  408.     /** Get the transform between offset frame and inertial frame.
  409.      * <p>
  410.      * The offset frame takes the <em>current</em> position offset,
  411.      * polar motion and the meridian shift into account. The frame
  412.      * returned is disconnected from later changes in the parameters.
  413.      * When the {@link ParameterDriver parameters} managing these
  414.      * offsets are changed, the method must be called again to retrieve
  415.      * a new offset frame.
  416.      * </p>
  417.      * @param inertial inertial frame to transform to
  418.      * @param clockDate date of the transform as read by the ground station clock (i.e. clock offset <em>not</em> compensated)
  419.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  420.      * date (i.e. with clock, Earth and station offsets applied)
  421.      */
  422.     public Transform getOffsetToInertial(final Frame inertial, final AbsoluteDate clockDate) {

  424.         // take clock offset into account
  425.         final double offset = clockOffsetDriver.getValue();
  426.         final AbsoluteDate offsetCompensatedDate = new AbsoluteDate(clockDate, -offset);

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

  431.         // take station offsets into account
  432.         final double    x          = eastOffsetDriver.getValue();
  433.         final double    y          = northOffsetDriver.getValue();
  434.         final double    z          = zenithOffsetDriver.getValue();
  435.         final BodyShape baseShape  = baseFrame.getParentShape();
  436.         final Transform baseToBody = baseFrame.getTransformTo(baseShape.getBodyFrame(), offsetCompensatedDate);
  437.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));
  438.         origin = origin.add(computeDisplacement(offsetCompensatedDate, origin));

  440.         final GeodeticPoint originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  441.         final Transform offsetToIntermediate =
  442.                         new Transform(offsetCompensatedDate,
  443.                                       new Transform(offsetCompensatedDate,
  444.                                                     new Rotation(Vector3D.PLUS_I, Vector3D.PLUS_K,
  445.                                                                  originGP.getEast(), originGP.getZenith()),
  446.                                                     Vector3D.ZERO),
  447.                                       new Transform(offsetCompensatedDate, origin));

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

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

  454.     }

  456.     /** Get the transform between offset frame and inertial frame with derivatives.
  457.      * <p>
  458.      * As the East and North vectors are not well defined at pole, the derivatives
  459.      * of these two vectors diverge to infinity as we get closer to the pole.
  460.      * So this method should not be used for stations less than 0.0001 degree from
  461.      * either poles.
  462.      * </p>
  463.      * @param inertial inertial frame to transform to
  464.      * @param clockDate date of the transform as read by the ground station clock (i.e. clock offset <em>not</em> compensated)
  465.      * @param factory factory for the derivatives
  466.      * @param indices indices of the estimated parameters in derivatives computations
  467.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  468.      * date (i.e. with clock, Earth and station offsets applied)
  469.      * @see #getOffsetToInertial(Frame, FieldAbsoluteDate, DSFactory, Map)
  470.      * @since 9.3
  471.      */
  472.     public FieldTransform<DerivativeStructure> getOffsetToInertial(final Frame inertial,
  473.                                                                    final AbsoluteDate clockDate,
  474.                                                                    final DSFactory factory,
  475.                                                                    final Map<String, Integer> indices) {
  476.         // take clock offset into account
  477.         final DerivativeStructure offset = clockOffsetDriver.getValue(factory, indices);
  478.         final FieldAbsoluteDate<DerivativeStructure> offsetCompensatedDate =
  479.                         new FieldAbsoluteDate<DerivativeStructure>(clockDate, offset.negate());

  481.         return getOffsetToInertial(inertial, offsetCompensatedDate, factory, indices);
  482.     }

  484.     /** Get the transform between offset frame and inertial frame with derivatives.
  485.      * <p>
  486.      * As the East and North vectors are not well defined at pole, the derivatives
  487.      * of these two vectors diverge to infinity as we get closer to the pole.
  488.      * So this method should not be used for stations less than 0.0001 degree from
  489.      * either poles.
  490.      * </p>
  491.      * @param inertial inertial frame to transform to
  492.      * @param offsetCompensatedDate date of the transform, clock offset and its derivatives already compensated
  493.      * @param factory factory for the derivatives
  494.      * @param indices indices of the estimated parameters in derivatives computations
  495.      * @return transform between offset frame and inertial frame, at specified date
  496.      * @see #getOffsetToInertial(Frame, AbsoluteDate, DSFactory, Map)
  497.      * @since 9.0
  498.      */
  499.     public FieldTransform<DerivativeStructure> getOffsetToInertial(final Frame inertial,
  500.                                                                    final FieldAbsoluteDate<DerivativeStructure> offsetCompensatedDate,
  501.                                                                    final DSFactory factory,
  502.                                                                    final Map<String, Integer> indices) {

  504.         final Field<DerivativeStructure>         field = factory.getDerivativeField();
  505.         final FieldVector3D<DerivativeStructure> zero  = FieldVector3D.getZero(field);
  506.         final FieldVector3D<DerivativeStructure> plusI = FieldVector3D.getPlusI(field);
  507.         final FieldVector3D<DerivativeStructure> plusK = FieldVector3D.getPlusK(field);

  509.         // take Earth offsets into account
  510.         final FieldTransform<DerivativeStructure> intermediateToBody =
  511.                         estimatedEarthFrameProvider.getTransform(offsetCompensatedDate, factory, indices).getInverse();

  513.         // take station offsets into account
  514.         final DerivativeStructure  x          = eastOffsetDriver.getValue(factory, indices);
  515.         final DerivativeStructure  y          = northOffsetDriver.getValue(factory, indices);
  516.         final DerivativeStructure  z          = zenithOffsetDriver.getValue(factory, indices);
  517.         final BodyShape            baseShape  = baseFrame.getParentShape();
  518.         final Transform            baseToBody = baseFrame.getTransformTo(baseShape.getBodyFrame(), (AbsoluteDate) null);

  520.         FieldVector3D<DerivativeStructure>            origin   = baseToBody.transformPosition(new FieldVector3D<>(x, y, z));
  521.         origin = origin.add(computeDisplacement(offsetCompensatedDate.toAbsoluteDate(), origin.toVector3D()));
  522.         final FieldGeodeticPoint<DerivativeStructure> originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  523.         final FieldTransform<DerivativeStructure> offsetToIntermediate =
  524.                         new FieldTransform<>(offsetCompensatedDate,
  525.                                              new FieldTransform<>(offsetCompensatedDate,
  526.                                                                   new FieldRotation<>(plusI, plusK,
  527.                                                                                       originGP.getEast(), originGP.getZenith()),
  528.                                                                   zero),
  529.                                              new FieldTransform<>(offsetCompensatedDate, origin));

  531.         // combine all transforms together
  532.         final FieldTransform<DerivativeStructure> bodyToInert        = baseFrame.getParent().getTransformTo(inertial, offsetCompensatedDate);

  534.         return new FieldTransform<>(offsetCompensatedDate,
  535.                                     offsetToIntermediate,
  536.                                     new FieldTransform<>(offsetCompensatedDate, intermediateToBody, bodyToInert));

  538.     }

  540. }
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