HalfTrackSampler.java

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 * this work for additional information regarding copyright ownership.
 * CS licenses this file to You under the Apache License, Version 2.0
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package org.orekit.models.earth.tessellation;

import java.util.ArrayList;
import java.util.List;

import org.hipparchus.util.Pair;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.bodies.OneAxisEllipsoid;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.sampling.OrekitFixedStepHandler;
import org.orekit.utils.TimeStampedPVCoordinates;

/** Sampler for half track span.
 * @since 7.1
 * @see AlongTrackAiming
 * @author Luc Maisonobe
 */
class HalfTrackSampler implements OrekitFixedStepHandler {

    /** Ellipsoid over which track is sampled. */
    private final OneAxisEllipsoid ellipsoid;

    /** Half track sample. */
    private final List<Pair<GeodeticPoint, TimeStampedPVCoordinates>> halfTrack;

    /** Simple constructor.
     * @param ellipsoid ellipsoid over which track is sampled
     */
    HalfTrackSampler(final OneAxisEllipsoid ellipsoid) {
        this.ellipsoid = ellipsoid;
        this.halfTrack = new ArrayList<Pair<GeodeticPoint, TimeStampedPVCoordinates>>();
    }

    /** Get half track sample.
     * @return half track sample
     */
    public List<Pair<GeodeticPoint, TimeStampedPVCoordinates>> getHalfTrack() {
        return halfTrack;
    }

    /** {@inheritDoc} */
    @Override
    public void handleStep(final SpacecraftState currentState) {

        // find the sliding ground point below spacecraft
        final TimeStampedPVCoordinates pv       = currentState.getPVCoordinates(ellipsoid.getBodyFrame());
        final TimeStampedPVCoordinates groundPV = ellipsoid.projectToGround(pv, ellipsoid.getBodyFrame());

        // geodetic coordinates
        final GeodeticPoint gp =
                        ellipsoid.transform(groundPV.getPosition(), ellipsoid.getBodyFrame(), currentState.getDate());

        halfTrack.add(new Pair<GeodeticPoint, TimeStampedPVCoordinates>(gp, groundPV));

    }

}