GroundStation.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.measurements;

  19. import java.util.Map;

  21. import org.hipparchus.CalculusFieldElement;
  22. import org.hipparchus.Field;
  23. import org.hipparchus.analysis.differentiation.Gradient;
  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.FieldStaticTransform;
  38. import org.orekit.frames.FieldTransform;
  39. import org.orekit.frames.Frame;
  40. import org.orekit.frames.FramesFactory;
  41. import org.orekit.frames.StaticTransform;
  42. import org.orekit.frames.TopocentricFrame;
  43. import org.orekit.frames.Transform;
  44. import org.orekit.models.earth.displacement.StationDisplacement;
  45. import org.orekit.time.AbsoluteDate;
  46. import org.orekit.time.FieldAbsoluteDate;
  47. import org.orekit.time.UT1Scale;
  48. import org.orekit.utils.ParameterDriver;

  50. /** Class modeling a ground station that can perform some measurements.
  51.  * <p>
  52.  * This class adds a position offset parameter to a base {@link TopocentricFrame
  53.  * topocentric frame}.
  54.  * </p>
  55.  * <p>
  56.  * Since 9.0, this class also adds parameters for an additional polar motion
  57.  * and an additional prime meridian orientation. Since these parameters will
  58.  * have the same name for all ground stations, they will be managed consistently
  59.  * and allow to estimate Earth orientation precisely (this is needed for precise
  60.  * orbit determination). The polar motion and prime meridian orientation will
  61.  * be applied <em>after</em> regular Earth orientation parameters, so the value
  62.  * of the estimated parameters will be correction to EOP, they will not be the
  63.  * complete EOP values by themselves. Basically, this means that for Earth, the
  64.  * following transforms are applied in order, between inertial frame and ground
  65.  * station frame (for non-Earth based ground stations, different precession nutation
  66.  * models and associated planet oritentation parameters would be applied, if available):
  67.  * </p>
  68.  * <p>
  69.  * Since 9.3, this class also adds a station clock offset parameter, which manages
  70.  * the value that must be subtracted from the observed measurement date to get the real
  71.  * physical date at which the measurement was performed (i.e. the offset is negative
  72.  * if the ground station clock is slow and positive if it is fast).
  73.  * </p>
  74.  * <ol>
  75.  *   <li>precession/nutation, as theoretical model plus celestial pole EOP parameters</li>
  76.  *   <li>body rotation, as theoretical model plus prime meridian EOP parameters</li>
  77.  *   <li>polar motion, which is only from EOP parameters (no theoretical models)</li>
  78.  *   <li>additional body rotation, controlled by {@link #getPrimeMeridianOffsetDriver()} and {@link #getPrimeMeridianDriftDriver()}</li>
  79.  *   <li>additional polar motion, controlled by {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()},
  80.  *   {@link #getPolarOffsetYDriver()} and {@link #getPolarDriftYDriver()}</li>
  81.  *   <li>station clock offset, controlled by {@link #getClockOffsetDriver()}</li>
  82.  *   <li>station position offset, controlled by {@link #getEastOffsetDriver()},
  83.  *   {@link #getNorthOffsetDriver()} and {@link #getZenithOffsetDriver()}</li>
  84.  * </ol>
  85.  * @author Luc Maisonobe
  86.  * @since 8.0
  87.  */
  88. public class GroundStation {

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

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

  96.     /** Suffix for ground clock drift parameters name.
  97.      * @since 12.1
  98.      */
  99.     public static final String ACCELERATION_SUFFIX = "-acceleration-clock";

  101.     /** Clock offset scaling factor.
  102.      * <p>
  103.      * We use a power of 2 to avoid numeric noise introduction
  104.      * in the multiplications/divisions sequences.
  105.      * </p>
  106.      */
  107.     private static final double CLOCK_OFFSET_SCALE = FastMath.scalb(1.0, -10);

  109.     /** Position offsets scaling factor.
  110.      * <p>
  111.      * We use a power of 2 (in fact really 1.0 here) to avoid numeric noise introduction
  112.      * in the multiplications/divisions sequences.
  113.      * </p>
  114.      */
  115.     private static final double POSITION_OFFSET_SCALE = FastMath.scalb(1.0, 0);

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

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

  123.     /** Base frame associated with the station. */
  124.     private final TopocentricFrame baseFrame;

  126.     /** Fundamental nutation arguments. */
  127.     private final FundamentalNutationArguments arguments;

  129.     /** Displacement models. */
  130.     private final StationDisplacement[] displacements;

  132.     /** Driver for clock offset. */
  133.     private final ParameterDriver clockOffsetDriver;

  135.     /** Driver for clock drift. */
  136.     private final ParameterDriver clockDriftDriver;

  138.     /** Driver for clock acceleration.
  139.      * @since 12.1
  140.      */
  141.     private final ParameterDriver clockAccelerationDriver;

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

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

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

  152.     /**
  153.      * Build a ground station ignoring {@link StationDisplacement station displacements}.
  154.      * <p>
  155.      * The initial values for the pole and prime meridian parametric linear models
  156.      * ({@link #getPrimeMeridianOffsetDriver()}, {@link #getPrimeMeridianDriftDriver()},
  157.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()}, {@link #getPolarOffsetXDriver()},
  158.      * {@link #getPolarDriftXDriver()}) are set to 0. The initial values for the station offset model
  159.      * ({@link #getClockOffsetDriver()}, {@link #getEastOffsetDriver()}, {@link #getNorthOffsetDriver()},
  160.      * {@link #getZenithOffsetDriver()}) are set to 0. This implies that as long as these values are not changed, the
  161.      * offset frame is the same as the {@link #getBaseFrame() base frame}. As soon as some of these models are changed,
  162.      * the offset frame moves away from the {@link #getBaseFrame() base frame}.
  163.      * </p>
  164.      *
  165.      * @param baseFrame base frame associated with the station, without *any* parametric model
  166.      *                  (no station offset, no polar motion, no meridian shift)
  167.      * @see #GroundStation(TopocentricFrame, EOPHistory, StationDisplacement...)
  168.      * @since 13.0
  169.      */
  170.     public GroundStation(final TopocentricFrame baseFrame) {
  171.         this(baseFrame, FramesFactory.findEOP(baseFrame));
  172.     }

  174.     /**
  175.      * Simple constructor.
  176.      * <p>
  177.      * The initial values for the pole and prime meridian parametric linear models
  178.      * ({@link #getPrimeMeridianOffsetDriver()}, {@link #getPrimeMeridianDriftDriver()},
  179.      * {@link #getPolarOffsetXDriver()}, {@link #getPolarDriftXDriver()}, {@link #getPolarOffsetXDriver()},
  180.      * {@link #getPolarDriftXDriver()}) are set to 0. The initial values for the station offset model
  181.      * ({@link #getClockOffsetDriver()}, {@link #getEastOffsetDriver()}, {@link #getNorthOffsetDriver()},
  182.      * {@link #getZenithOffsetDriver()}, {@link #getClockOffsetDriver()}) are set to 0. This implies that as long as
  183.      * these values are not changed, the offset frame is the same as the {@link #getBaseFrame() base frame}. As soon as
  184.      * some of these models are changed, the offset frame moves away from the {@link #getBaseFrame() base frame}.
  185.      * </p>
  186.      *
  187.      * @param baseFrame     base frame associated with the station, without *any* parametric model (no station offset,
  188.      *                      no polar motion, no meridian shift)
  189.      * @param eopHistory    EOP history associated with Earth frames
  190.      * @param displacements ground station displacement model (tides, ocean loading, atmospheric loading, thermal
  191.      *                      effects...)
  192.      * @since 12.1
  193.      */
  194.     public GroundStation(final TopocentricFrame baseFrame, final EOPHistory eopHistory,
  195.                          final StationDisplacement... displacements) {

  197.         this.baseFrame = baseFrame;

  199.         if (eopHistory == null) {
  200.             throw new OrekitException(OrekitMessages.NO_EARTH_ORIENTATION_PARAMETERS);
  201.         }

  203.         final UT1Scale baseUT1 = eopHistory.getTimeScales()
  204.                 .getUT1(eopHistory.getConventions(), eopHistory.isSimpleEop());
  205.         this.estimatedEarthFrameProvider = new EstimatedEarthFrameProvider(baseUT1);
  206.         this.estimatedEarthFrame = new Frame(baseFrame.getParent(), estimatedEarthFrameProvider,
  207.                                              baseFrame.getParent() + "-estimated");

  209.         if (displacements.length == 0) {
  210.             arguments = null;
  211.         } else {
  212.             arguments = eopHistory.getConventions().getNutationArguments(
  213.                     estimatedEarthFrameProvider.getEstimatedUT1(),
  214.                     eopHistory.getTimeScales());
  215.         }

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

  219.         this.clockOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-clock",
  220.                                                      0.0, CLOCK_OFFSET_SCALE,
  221.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  223.         this.clockDriftDriver = new ParameterDriver(baseFrame.getName() + DRIFT_SUFFIX,
  224.                                                     0.0, CLOCK_OFFSET_SCALE,
  225.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  227.         this.clockAccelerationDriver = new ParameterDriver(baseFrame.getName() + ACCELERATION_SUFFIX,
  228.                                                     0.0, CLOCK_OFFSET_SCALE,
  229.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  231.         this.eastOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-East",
  232.                                                     0.0, POSITION_OFFSET_SCALE,
  233.                                                     Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  235.         this.northOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-North",
  236.                                                      0.0, POSITION_OFFSET_SCALE,
  237.                                                      Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  239.         this.zenithOffsetDriver = new ParameterDriver(baseFrame.getName() + OFFSET_SUFFIX + "-Zenith",
  240.                                                       0.0, POSITION_OFFSET_SCALE,
  241.                                                       Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);

  243.     }

  245.     /** Get the displacement models.
  246.      * @return displacement models (empty if no model has been set up)
  247.      * @since 9.1
  248.      */
  249.     public StationDisplacement[] getDisplacements() {
  250.         return displacements.clone();
  251.     }

  253.     /** Get a driver allowing to change station clock (which is related to measurement date).
  254.      * @return driver for station clock offset
  255.      * @since 9.3
  256.      */
  257.     public ParameterDriver getClockOffsetDriver() {
  258.         return clockOffsetDriver;
  259.     }

  261.     /** Get a driver allowing to change station clock drift (which is related to measurement date).
  262.      * @return driver for station clock drift
  263.      * @since 10.3
  264.      */
  265.     public ParameterDriver getClockDriftDriver() {
  266.         return clockDriftDriver;
  267.     }

  269.     /** Get a driver allowing to change station clock acceleration (which is related to measurement date).
  270.      * @return driver for station clock acceleration
  271.      * @since 12.1
  272.      */
  273.     public ParameterDriver getClockAccelerationDriver() {
  274.         return clockAccelerationDriver;
  275.     }

  277.     /** Get a driver allowing to change station position along East axis.
  278.      * @return driver for station position offset along East axis
  279.      */
  280.     public ParameterDriver getEastOffsetDriver() {
  281.         return eastOffsetDriver;
  282.     }

  284.     /** Get a driver allowing to change station position along North axis.
  285.      * @return driver for station position offset along North axis
  286.      */
  287.     public ParameterDriver getNorthOffsetDriver() {
  288.         return northOffsetDriver;
  289.     }

  291.     /** Get a driver allowing to change station position along Zenith axis.
  292.      * @return driver for station position offset along Zenith axis
  293.      */
  294.     public ParameterDriver getZenithOffsetDriver() {
  295.         return zenithOffsetDriver;
  296.     }

  298.     /** Get a driver allowing to add a prime meridian rotation.
  299.      * <p>
  300.      * The parameter is an angle in radians. In order to convert this
  301.      * value to a DUT1 in seconds, the value must be divided by
  302.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  303.      * of Earth from the TIRF model).
  304.      * </p>
  305.      * @return driver for prime meridian rotation
  306.      */
  307.     public ParameterDriver getPrimeMeridianOffsetDriver() {
  308.         return estimatedEarthFrameProvider.getPrimeMeridianOffsetDriver();
  309.     }

  311.     /** Get a driver allowing to add a prime meridian rotation rate.
  312.      * <p>
  313.      * The parameter is an angle rate in radians per second. In order to convert this
  314.      * value to a LOD in seconds, the value must be multiplied by -86400 and divided by
  315.      * {@code ave = 7.292115146706979e-5} (which is the nominal Angular Velocity
  316.      * of Earth from the TIRF model).
  317.      * </p>
  318.      * @return driver for prime meridian rotation rate
  319.      */
  320.     public ParameterDriver getPrimeMeridianDriftDriver() {
  321.         return estimatedEarthFrameProvider.getPrimeMeridianDriftDriver();
  322.     }

  324.     /** Get a driver allowing to add a polar offset along X.
  325.      * <p>
  326.      * The parameter is an angle in radians
  327.      * </p>
  328.      * @return driver for polar offset along X
  329.      */
  330.     public ParameterDriver getPolarOffsetXDriver() {
  331.         return estimatedEarthFrameProvider.getPolarOffsetXDriver();
  332.     }

  334.     /** Get a driver allowing to add a polar drift along X.
  335.      * <p>
  336.      * The parameter is an angle rate in radians per second
  337.      * </p>
  338.      * @return driver for polar drift along X
  339.      */
  340.     public ParameterDriver getPolarDriftXDriver() {
  341.         return estimatedEarthFrameProvider.getPolarDriftXDriver();
  342.     }

  344.     /** Get a driver allowing to add a polar offset along Y.
  345.      * <p>
  346.      * The parameter is an angle in radians
  347.      * </p>
  348.      * @return driver for polar offset along Y
  349.      */
  350.     public ParameterDriver getPolarOffsetYDriver() {
  351.         return estimatedEarthFrameProvider.getPolarOffsetYDriver();
  352.     }

  354.     /** Get a driver allowing to add a polar drift along Y.
  355.      * <p>
  356.      * The parameter is an angle rate in radians per second
  357.      * </p>
  358.      * @return driver for polar drift along Y
  359.      */
  360.     public ParameterDriver getPolarDriftYDriver() {
  361.         return estimatedEarthFrameProvider.getPolarDriftYDriver();
  362.     }

  364.     /** Get the base frame associated with the station.
  365.      * <p>
  366.      * The base frame corresponds to a null position offset, null
  367.      * polar motion, null meridian shift
  368.      * </p>
  369.      * @return base frame associated with the station
  370.      */
  371.     public TopocentricFrame getBaseFrame() {
  372.         return baseFrame;
  373.     }

  375.     /** Get the estimated Earth frame, including the estimated linear models for pole and prime meridian.
  376.      * <p>
  377.      * This frame is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  378.      * {@link #getPrimeMeridianDriftDriver() driver prime meridian drift},
  379.      * {@link #getPolarOffsetXDriver() driver for polar offset along X},
  380.      * {@link #getPolarDriftXDriver() driver for polar drift along X},
  381.      * {@link #getPolarOffsetYDriver() driver for polar offset along Y},
  382.      * {@link #getPolarDriftYDriver() driver for polar drift along Y}, so its orientation changes when
  383.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  384.      * </p>
  385.      * @return estimated Earth frame
  386.      * @since 9.1
  387.      */
  388.     public Frame getEstimatedEarthFrame() {
  389.         return estimatedEarthFrame;
  390.     }

  392.     /** Get the estimated UT1 scale, including the estimated linear models for prime meridian.
  393.      * <p>
  394.      * This time scale is bound to the {@link #getPrimeMeridianOffsetDriver() driver for prime meridian offset},
  395.      * and {@link #getPrimeMeridianDriftDriver() driver prime meridian drift}, so its offset from UTC changes when
  396.      * the {@link ParameterDriver#setValue(double) setValue} methods of the drivers are called.
  397.      * </p>
  398.      * @return estimated Earth frame
  399.      * @since 9.1
  400.      */
  401.     public UT1Scale getEstimatedUT1() {
  402.         return estimatedEarthFrameProvider.getEstimatedUT1();
  403.     }

  405.     /** Get the station displacement.
  406.      * @param date current date
  407.      * @param position raw position of the station in Earth frame
  408.      * before displacement is applied
  409.      * @return station displacement
  410.      * @since 9.1
  411.      */
  412.     private Vector3D computeDisplacement(final AbsoluteDate date, final Vector3D position) {
  413.         Vector3D displacement = Vector3D.ZERO;
  414.         if (arguments != null) {
  415.             final BodiesElements elements = arguments.evaluateAll(date);
  416.             for (final StationDisplacement sd : displacements) {
  417.                 // we consider all displacements apply to the same initial position,
  418.                 // i.e. they apply simultaneously, not according to some order
  419.                 displacement = displacement.add(sd.displacement(elements, estimatedEarthFrame, position));
  420.             }
  421.         }
  422.         return displacement;
  423.     }

  425.     /** Get the geodetic point at the center of the offset frame.
  426.      * @param date current date (may be null if displacements are ignored)
  427.      * @return geodetic point at the center of the offset frame
  428.      * @since 9.1
  429.      */
  430.     public GeodeticPoint getOffsetGeodeticPoint(final AbsoluteDate date) {

  432.         // take station offset into account
  433.         final double    x          = eastOffsetDriver.getValue();
  434.         final double    y          = northOffsetDriver.getValue();
  435.         final double    z          = zenithOffsetDriver.getValue();
  436.         final BodyShape baseShape  = baseFrame.getParentShape();
  437.         final StaticTransform baseToBody = baseFrame.getStaticTransformTo(baseShape.getBodyFrame(), date);
  438.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));

  440.         if (date != null) {
  441.             origin = origin.add(computeDisplacement(date, origin));
  442.         }

  444.         return baseShape.transform(origin, baseShape.getBodyFrame(), date);

  446.     }

  448.     /** Get the geodetic point at the center of the offset frame.
  449.      * @param <T> type of the field elements
  450.      * @param date current date(<em>must</em> be non-null, which is a more stringent condition
  451.      *      *                    than in {@link #getOffsetGeodeticPoint(AbsoluteDate)}
  452.      * @return geodetic point at the center of the offset frame
  453.      * @since 12.1
  454.      */
  455.     public <T extends CalculusFieldElement<T>> FieldGeodeticPoint<T> getOffsetGeodeticPoint(final FieldAbsoluteDate<T> date) {

  457.         // take station offset into account
  458.         final double    x          = eastOffsetDriver.getValue();
  459.         final double    y          = northOffsetDriver.getValue();
  460.         final double    z          = zenithOffsetDriver.getValue();
  461.         final BodyShape baseShape  = baseFrame.getParentShape();
  462.         final FieldStaticTransform<T> baseToBody = baseFrame.getStaticTransformTo(baseShape.getBodyFrame(), date);
  463.         FieldVector3D<T> origin    = baseToBody.transformPosition(new Vector3D(x, y, z));
  464.         origin = origin.add(computeDisplacement(date.toAbsoluteDate(), origin.toVector3D()));

  466.         return baseShape.transform(origin, baseShape.getBodyFrame(), date);

  468.     }

  470.     /** Get the transform between offset frame and inertial frame.
  471.      * <p>
  472.      * The offset frame takes the <em>current</em> position offset,
  473.      * polar motion and the meridian shift into account. The frame
  474.      * returned is disconnected from later changes in the parameters.
  475.      * When the {@link ParameterDriver parameters} managing these
  476.      * offsets are changed, the method must be called again to retrieve
  477.      * a new offset frame.
  478.      * </p>
  479.      * @param inertial inertial frame to transform to
  480.      * @param date date of the transform
  481.      * @param clockOffsetAlreadyApplied if true, the specified {@code date} is as read
  482.      * by the ground station clock (i.e. clock offset <em>not</em> compensated), if false,
  483.      * the specified {@code date} was already compensated and is a physical absolute date
  484.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  485.      * date (i.e. with clock, Earth and station offsets applied)
  486.      */
  487.     public Transform getOffsetToInertial(final Frame inertial,
  488.                                          final AbsoluteDate date, final boolean clockOffsetAlreadyApplied) {

  490.         // take clock offset into account
  491.         final AbsoluteDate offsetCompensatedDate = clockOffsetAlreadyApplied ?
  492.                                                    date :
  493.                                                    new AbsoluteDate(date, -clockOffsetDriver.getValue());

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

  498.         // take station offsets into account
  499.         final double    x          = eastOffsetDriver.getValue();
  500.         final double    y          = northOffsetDriver.getValue();
  501.         final double    z          = zenithOffsetDriver.getValue();
  502.         final BodyShape baseShape  = baseFrame.getParentShape();
  503.         final StaticTransform baseToBody = baseFrame
  504.                 .getStaticTransformTo(baseShape.getBodyFrame(), offsetCompensatedDate);
  505.         Vector3D        origin     = baseToBody.transformPosition(new Vector3D(x, y, z));
  506.         origin = origin.add(computeDisplacement(offsetCompensatedDate, origin));

  508.         final GeodeticPoint originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  509.         final Transform offsetToIntermediate =
  510.                         new Transform(offsetCompensatedDate,
  511.                                       new Transform(offsetCompensatedDate,
  512.                                                     new Rotation(Vector3D.PLUS_I, Vector3D.PLUS_K,
  513.                                                                  originGP.getEast(), originGP.getZenith()),
  514.                                                     Vector3D.ZERO),
  515.                                       new Transform(offsetCompensatedDate, origin));

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

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

  522.     }

  524.     /** Get the transform between offset frame and inertial frame with derivatives.
  525.      * <p>
  526.      * As the East and North vectors are not well defined at pole, the derivatives
  527.      * of these two vectors diverge to infinity as we get closer to the pole.
  528.      * So this method should not be used for stations less than 0.0001 degree from
  529.      * either poles.
  530.      * </p>
  531.      * @param inertial inertial frame to transform to
  532.      * @param clockDate date of the transform as read by the ground station clock (i.e. clock offset <em>not</em> compensated)
  533.      * @param freeParameters total number of free parameters in the gradient
  534.      * @param indices indices of the estimated parameters in derivatives computations, must be driver
  535.      * span name in map, not driver name or will not give right results (see {@link ParameterDriver#getValue(int, Map)})
  536.      * @return transform between offset frame and inertial frame, at <em>real</em> measurement
  537.      * date (i.e. with clock, Earth and station offsets applied)
  538.      * @see #getOffsetToInertial(Frame, FieldAbsoluteDate, int, Map)
  539.      * @since 10.2
  540.      */
  541.     public FieldTransform<Gradient> getOffsetToInertial(final Frame inertial,
  542.                                                         final AbsoluteDate clockDate,
  543.                                                         final int freeParameters,
  544.                                                         final Map<String, Integer> indices) {
  545.         // take clock offset into account
  546.         final Gradient offset = clockOffsetDriver.getValue(freeParameters, indices, clockDate);
  547.         final FieldAbsoluteDate<Gradient> offsetCompensatedDate =
  548.                         new FieldAbsoluteDate<>(clockDate, offset.negate());

  550.         return getOffsetToInertial(inertial, offsetCompensatedDate, freeParameters, indices);
  551.     }

  553.     /** Get the transform between offset frame and inertial frame with derivatives.
  554.      * <p>
  555.      * As the East and North vectors are not well defined at pole, the derivatives
  556.      * of these two vectors diverge to infinity as we get closer to the pole.
  557.      * So this method should not be used for stations less than 0.0001 degree from
  558.      * either poles.
  559.      * </p>
  560.      * @param inertial inertial frame to transform to
  561.      * @param offsetCompensatedDate date of the transform, clock offset and its derivatives already compensated
  562.      * @param freeParameters total number of free parameters in the gradient
  563.      * @param indices indices of the estimated parameters in derivatives computations, must be driver
  564.      * span name in map, not driver name or will not give right results (see {@link ParameterDriver#getValue(int, Map)})
  565.      * @return transform between offset frame and inertial frame, at specified date
  566.      * @since 10.2
  567.      */
  568.     public FieldTransform<Gradient> getOffsetToInertial(final Frame inertial,
  569.                                                         final FieldAbsoluteDate<Gradient> offsetCompensatedDate,
  570.                                                         final int freeParameters,
  571.                                                         final Map<String, Integer> indices) {

  573.         final Field<Gradient>         field = offsetCompensatedDate.getField();
  574.         final FieldVector3D<Gradient> zero  = FieldVector3D.getZero(field);
  575.         final FieldVector3D<Gradient> plusI = FieldVector3D.getPlusI(field);
  576.         final FieldVector3D<Gradient> plusK = FieldVector3D.getPlusK(field);

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

  582.         // take station offsets into account
  583.         final Gradient                       x          = eastOffsetDriver.getValue(freeParameters, indices);
  584.         final Gradient                       y          = northOffsetDriver.getValue(freeParameters, indices);
  585.         final Gradient                       z          = zenithOffsetDriver.getValue(freeParameters, indices);
  586.         final BodyShape                      baseShape  = baseFrame.getParentShape();
  587.         final FieldStaticTransform<Gradient> baseToBody = baseFrame.getStaticTransformTo(baseShape.getBodyFrame(), offsetCompensatedDate);

  589.         FieldVector3D<Gradient> origin = baseToBody.transformPosition(new FieldVector3D<>(x, y, z));
  590.         origin = origin.add(computeDisplacement(offsetCompensatedDate.toAbsoluteDate(), origin.toVector3D()));
  591.         final FieldGeodeticPoint<Gradient> originGP = baseShape.transform(origin, baseShape.getBodyFrame(), offsetCompensatedDate);
  592.         final FieldTransform<Gradient> offsetToIntermediate =
  593.                         new FieldTransform<>(offsetCompensatedDate,
  594.                                              new FieldTransform<>(offsetCompensatedDate,
  595.                                                                   new FieldRotation<>(plusI, plusK,
  596.                                                                                       originGP.getEast(), originGP.getZenith()),
  597.                                                                   zero),
  598.                                              new FieldTransform<>(offsetCompensatedDate, origin));

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

  603.         return new FieldTransform<>(offsetCompensatedDate,
  604.                                     offsetToIntermediate,
  605.                                     new FieldTransform<>(offsetCompensatedDate, intermediateToBody, bodyToInert));

  607.     }

  609. }
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