SimpleExponentialAtmosphere.java

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package org.orekit.models.earth.atmosphere;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.FieldGeodeticPoint;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;


/** Simple exponential atmospheric model.
 * <p>This model represents a simple atmosphere with an exponential
 * density and rigidly bound to the underlying rotating body.</p>
 * @author Fabien Maussion
 * @author Luc Maisonobe
 */
public class SimpleExponentialAtmosphere implements Atmosphere {

    /** Serializable UID.*/
    private static final long serialVersionUID = 2772347498196369601L;

    /** Earth shape model. */
    private BodyShape    shape;

    /** Reference density. */
    private double       rho0;

    /** Reference altitude. */
    private double       h0;

    /** Reference altitude scale. */
    private double       hscale;

    /** Create an exponential atmosphere.
     * @param shape body shape model
     * @param rho0 Density at the altitude h0
     * @param h0 Altitude of reference (m)
     * @param hscale Scale factor
     */
    public SimpleExponentialAtmosphere(final BodyShape shape, final double rho0,
                                       final double h0, final double hscale) {
        this.shape  = shape;
        this.rho0   = rho0;
        this.h0     = h0;
        this.hscale = hscale;
    }

    /** {@inheritDoc} */
    public Frame getFrame() {
        return shape.getBodyFrame();
    }

    /** {@inheritDoc} */
    public double getDensity(final AbsoluteDate date, final Vector3D position, final Frame frame) {
        final GeodeticPoint gp = shape.transform(position, frame, date);
        return rho0 * FastMath.exp((h0 - gp.getAltitude()) / hscale);
    }

    @Override
    public <T extends CalculusFieldElement<T>> T
        getDensity(final FieldAbsoluteDate<T> date, final FieldVector3D<T> position,
                   final Frame frame) {
        final FieldGeodeticPoint<T> gp = shape.transform(position, frame, date);
        return gp.getAltitude().subtract(h0).divide(-hscale).exp().multiply(rho0);
    }

}