FixedPointTleGenerationAlgorithm.java

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package org.orekit.propagation.analytical.tle.generation;

import org.hipparchus.CalculusFieldElement;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.frames.Frame;
import org.orekit.orbits.FieldKeplerianOrbit;
import org.orekit.orbits.KeplerianOrbit;
import org.orekit.orbits.OrbitType;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.analytical.tle.FieldTLE;
import org.orekit.propagation.analytical.tle.TLE;
import org.orekit.propagation.conversion.osc2mean.FixedPointConverter;
import org.orekit.propagation.conversion.osc2mean.TLETheory;
import org.orekit.time.TimeScale;
import org.orekit.utils.ParameterDriver;

/**
 * Fixed Point method to reverse SGP4 and SDP4 propagation algorithm
 * and generate a usable TLE from a spacecraft state.
 * <p>
 * Using this algorithm, the B* value is not computed. In other words,
 * the B* value from the template TLE is set to the generated one.
 * </p>
 * @author Thomas Paulet
 * @author Bryan Cazabonne
 * @since 12.0
 */
public class FixedPointTleGenerationAlgorithm implements TleGenerationAlgorithm {

    /** Default value for epsilon. */
    public static final double EPSILON_DEFAULT = 1.0e-10;

    /** Default value for maxIterations. */
    public static final int MAX_ITERATIONS_DEFAULT = 100;

    /** Default value for scale. */
    public static final double SCALE_DEFAULT = 1.0;

    /** Osculating to mean orbit converter. */
    private final FixedPointConverter converter;

    /** UTC time scale. */
    private final TimeScale utc;

    /**
     * Default constructor.
     * <p>
     * Uses the {@link DataContext#getDefault() default data context}
     * as well as {@link #EPSILON_DEFAULT}, {@link #MAX_ITERATIONS_DEFAULT},
     * {@link #SCALE_DEFAULT} for method convergence.
     * </p>
     */
    @DefaultDataContext
    public FixedPointTleGenerationAlgorithm() {
        this(EPSILON_DEFAULT, MAX_ITERATIONS_DEFAULT, SCALE_DEFAULT);
    }

    /**
     * Constructor.
     * <p>
     * Uses the {@link DataContext#getDefault() default data context}.
     * </p>
     * @param epsilon used to compute threshold for convergence check
     * @param maxIterations maximum number of iterations for convergence
     * @param scale scale factor of the Fixed Point algorithm
     */
    @DefaultDataContext
    public FixedPointTleGenerationAlgorithm(final double epsilon,
                                            final int maxIterations,
                                            final double scale) {
        this(epsilon, maxIterations, scale,
             DataContext.getDefault().getTimeScales().getUTC(),
             DataContext.getDefault().getFrames().getTEME());
    }

    /**
     * Constructor.
     * @param epsilon used to compute threshold for convergence check
     * @param maxIterations maximum number of iterations for convergence
     * @param scale scale factor of the Fixed Point algorithm
     * @param utc UTC time scale
     * @param teme TEME frame
     */
    public FixedPointTleGenerationAlgorithm(final double epsilon,
                                            final int maxIterations,
                                            final double scale,
                                            final TimeScale utc,
                                            final Frame teme) {
        this.converter = new FixedPointConverter(new TLETheory(utc, teme),
                                                 epsilon,
                                                 maxIterations,
                                                 scale);
        this.utc       = utc;
    }

    /** {@inheritDoc} */
    @Override
    public TLE generate(final SpacecraftState state, final TLE templateTLE) {
        final KeplerianOrbit mean = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(converter.convertToMean(state.getOrbit()));
        final TLE tle = TleGenerationUtil.newTLE(mean, templateTLE, templateTLE.getBStar(mean.getDate()), utc);
        // reset estimated parameters from template to generated tle
        for (final ParameterDriver templateDrivers : templateTLE.getParametersDrivers()) {
            if (templateDrivers.isSelected()) {
                // set to selected for the new TLE
                tle.getParameterDriver(templateDrivers.getName()).setSelected(true);
            }
        }
        return tle;
    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> FieldTLE<T> generate(final FieldSpacecraftState<T> state,
                                                                    final FieldTLE<T> templateTLE) {
        final T bStar = state.getMass().getField().getZero().newInstance(templateTLE.getBStar());
        final FieldKeplerianOrbit<T> mean = (FieldKeplerianOrbit<T>) OrbitType.KEPLERIAN.convertType(converter.convertToMean(state.getOrbit()));
        final FieldTLE<T> tle = TleGenerationUtil.newTLE(mean, templateTLE, bStar, utc);
        // reset estimated parameters from template to generated tle
        for (final ParameterDriver templateDrivers : templateTLE.getParametersDrivers()) {
            if (templateDrivers.isSelected()) {
                // set to selected for the new TLE
                tle.getParameterDriver(templateDrivers.getName()).setSelected(true);
            }
        }
        return tle;
    }

}