BistaticModifierUtil.java

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package org.orekit.estimation.measurements.modifiers;

import java.util.Arrays;

import org.hipparchus.analysis.differentiation.Gradient;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.GroundStation;
import org.orekit.estimation.measurements.ObservedMeasurement;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.integration.AbstractGradientConverter;
import org.orekit.utils.Differentiation;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParametersDriversProvider;

/** Utility class for bistatic measurements.
 * @author Pascal Parraud
 * @since 11.2
 */
class BistaticModifierUtil {

    /** Private constructor for utility class.*/
    private BistaticModifierUtil() {
        // not used
    }

    /** Apply a modifier to an estimated measurement.
     * @param <T> type of the measurement
     * @param estimated estimated measurement to modify
     * @param emitter emitter station
     * @param receiver receiver station
     * @param converter gradient converter
     * @param parametricModel parametric modifier model
     * @param modelEffect model effect
     * @param modelEffectGradient model effect gradient
     */
    public static <T extends ObservedMeasurement<T>> void modify(final EstimatedMeasurement<T> estimated,
                                                                 final ParametersDriversProvider parametricModel,
                                                                 final AbstractGradientConverter converter,
                                                                 final GroundStation emitter, final GroundStation receiver,
                                                                 final ParametricModelEffect modelEffect,
                                                                 final ParametricModelEffectGradient modelEffectGradient) {

        final SpacecraftState state    = estimated.getStates()[0];
        final double[]        oldValue = estimated.getEstimatedValue();

        // update estimated derivatives with Jacobian of the measure wrt state
        final FieldSpacecraftState<Gradient> gState = converter.getState(parametricModel);
        final Gradient[] gParameters = converter.getParameters(gState, parametricModel);

        final Gradient delayUp = modelEffectGradient.evaluate(emitter, gState, gParameters);
        final double[] derivativesUp = delayUp.getGradient();

        final Gradient delayDown = modelEffectGradient.evaluate(receiver, gState, gParameters);
        final double[] derivativesDown = delayDown.getGradient();

        // update estimated derivatives with Jacobian of the measure wrt state
        final double[][] stateDerivatives = estimated.getStateDerivatives(0);
        for (int jcol = 0; jcol < stateDerivatives[0].length; ++jcol) {
            stateDerivatives[0][jcol] += derivativesUp[jcol];
            stateDerivatives[0][jcol] += derivativesDown[jcol];
        }
        estimated.setStateDerivatives(0, stateDerivatives);

        int index = 0;
        for (final ParameterDriver driver : parametricModel.getParametersDrivers()) {
            if (driver.isSelected()) {
                // update estimated derivatives with derivative of the modification wrt model parameters
                double parameterDerivative  = estimated.getParameterDerivatives(driver)[0];
                parameterDerivative += derivativesUp[index + converter.getFreeStateParameters()];
                parameterDerivative += derivativesDown[index + converter.getFreeStateParameters()];
                estimated.setParameterDerivatives(driver, parameterDerivative);
                index++;
            }

        }

        for (final ParameterDriver driver : Arrays.asList(emitter.getEastOffsetDriver(),
                                                          emitter.getNorthOffsetDriver(),
                                                          emitter.getZenithOffsetDriver())) {
            if (driver.isSelected()) {
                // update estimated derivatives with derivative of the modification wrt station parameters
                double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
                parameterDerivative += Differentiation.differentiate(d -> modelEffect.evaluate(emitter, state),
                                                                     3, 10.0 * driver.getScale()).value(driver);
                estimated.setParameterDerivatives(driver, parameterDerivative);
            }
        }

        for (final ParameterDriver driver : Arrays.asList(receiver.getClockOffsetDriver(),
                                                          receiver.getEastOffsetDriver(),
                                                          receiver.getNorthOffsetDriver(),
                                                          receiver.getZenithOffsetDriver())) {
            if (driver.isSelected()) {
                // update estimated derivatives with derivative of the modification wrt station parameters
                double parameterDerivative = estimated.getParameterDerivatives(driver)[0];
                parameterDerivative += Differentiation.differentiate(d -> modelEffect.evaluate(receiver, state),
                                                                     3, 10.0 * driver.getScale()).value(driver);
                estimated.setParameterDerivatives(driver, parameterDerivative);
            }
        }

        // update estimated value taking into account the model effect.
        // The model effect delay is directly added to the measurement.
        final double[] newValue = oldValue.clone();
        newValue[0] += delayUp.getValue();
        newValue[0] += delayDown.getValue();
        estimated.setEstimatedValue(newValue);

    }

}