ObservedMeasurement.java

/* Copyright 2002-2019 CS Systèmes d'Information
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 *
 *   http://www.apache.org/licenses/LICENSE-2.0
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 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.orekit.estimation.measurements;

import java.util.List;
import java.util.stream.Collectors;

import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.ParameterDriver;


/** Interface for measurements used for orbit determination.
 * <p>
 * The most important methods of this interface allow to:
 * <ul>
 *   <li>get the observed value,</li>
 *   <li>estimate the theoretical value of a measurement,</li>
 *   <li>compute the corresponding partial derivatives (with respect to state and parameters)</li>
 * </ul>
 *
 * <p>
 * The estimated theoretical values can be modified by registering one or several {@link
 * EstimationModifier EstimationModifier} objects. These objects will manage notions
 * like tropospheric delays, biases, ...
 * </p>
 * @param <T> the type of the measurement
 * @author Luc Maisonobe
 * @since 8.0
 */
public interface ObservedMeasurement<T extends ObservedMeasurement<T>> extends ComparableMeasurement {

    /** Enable or disable a measurement.
     * <p>
     * Disabling a measurement allow to not consider it at
     * one stage of the orbit determination (for example when
     * it appears to be an outlier as per current estimated
     * covariance).
     * </p>
     * @param enabled if true the measurement will be enabled,
     * otherwise it will be disabled
     */
    void setEnabled(boolean enabled);

    /** Check if a measurement is enabled.
     * @return true if the measurement is enabled
     */
    boolean isEnabled();

    /** Get the dimension of the measurement.
     * <p>
     * Dimension is the size of the array containing the
     * value. It will be one for a scalar measurement like
     * a range or range-rate, but 6 for a position-velocity
     * measurement.
     * </p>
     * @return dimension of the measurement
     */
    int getDimension();

    /** Get the theoretical standard deviation.
     * <p>
     * The theoretical standard deviation is a theoretical value
     * used for normalizing the residuals. It acts as a weighting
     * factor to mix appropriately measurements with different units
     * and different accuracy. The value has the same dimension as
     * the measurement itself (i.e. when a residual is divided by
     * this value, it becomes dimensionless).
     * </p>
     * @return expected standard deviation
     * @see #getBaseWeight()
     */
    double[] getTheoreticalStandardDeviation();

    /** Get the base weight associated with the measurement
     * <p>
     * The base weight is used on residuals already normalized thanks to
     * {@link #getTheoreticalStandardDeviation()} to increase or
     * decrease relative effect of some measurements with respect to
     * other measurements. It is a dimensionless value, typically between
     * 0 and 1 (but it can really have any non-negative value).
     * </p>
     * @return base weight
     * @see #getTheoreticalStandardDeviation()
     * @see EstimatedMeasurement#getCurrentWeight()
     */
    double[] getBaseWeight();

    /** Add a modifier.
     * <p>
     * The modifiers are applied in the order in which they are added in order to
     * {@link #estimate(int, int, SpacecraftState[]) estimate} the measurement.
     * </p>
     * @param modifier modifier to add
     * @see #getModifiers()
     */
    void addModifier(EstimationModifier<T> modifier);

    /** Get the modifiers that apply to a measurement.
     * @return modifiers that apply to a measurement
     * @see #addModifier(EstimationModifier)
     */
    List<EstimationModifier<T>> getModifiers();

    /** Get the drivers for this measurement parameters, including its modifiers parameters.
     * @return drivers for this measurement parameters, including its modifiers parameters
     */
    List<ParameterDriver> getParametersDrivers();

    /** Get the indices of the {@link org.orekit.propagation.Propagator propagators}
     * related to this measurement.
     * <p>
     * The propagators are indexed starting from 0 and ordered according to
     * the order of the {@link org.orekit.propagation.conversion.PropagatorBuilder
     * propagators builders} in the orbit determination engine used.
     * </p>
     * @return indices of the {@link org.orekit.propagation.Propagator propagators}
     * related to this measurement
     * @since 9.0
     * @deprecated as of 9.3, replaced by {@link #getSatellites()}
     */
    @Deprecated
    List<Integer> getPropagatorsIndices();

    /** Get the satellites related to this measurement.
     * @return satellites related to this measurement
     * @since 9.3
     */
    default List<ObservableSatellite> getSatellites() {
        // this default implementation is temporary for the 9.3 release,
        // it will be removed when getPropagatorsIndices() is removed at 10.0
        return getPropagatorsIndices().stream().map(i -> new ObservableSatellite(i)).collect(Collectors.toList());
    }

    /** Estimate the theoretical value of the measurement.
     * <p>
     * The estimated value is the <em>combination</em> of the raw estimated
     * value and all the modifiers that apply to the measurement.
     * </p>
     * @param iteration iteration number
     * @param evaluation evaluations number
     * @param states orbital states at measurement date
     * @return estimated measurement
     */
    EstimatedMeasurement<T> estimate(int iteration, int evaluation, SpacecraftState[] states);

}