/* Copyright 2002-2017 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.attitudes;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.orekit.bodies.Ellipsoid;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
/**
* This class handles body center pointing attitude provider.
* <p>
* This class represents the attitude provider where the satellite z axis is
* pointing to the body frame center.</p>
* <p>
* The object <code>BodyCenterPointing</code> is guaranteed to be immutable.
* </p>
* @see GroundPointing
* @author Véronique Pommier-Maurussane
*/
public class FieldBodyCenterPointing<T extends RealFieldElement<T>> extends FieldGroundPointing<T> {
/** Body ellipsoid. */
private final Ellipsoid ellipsoid;
/** Creates new instance.
* @param inertialFrame frame in which orbital velocities are computed
* @param shape Body shape
* @exception OrekitException if the frame specified is not a pseudo-inertial frame
* @since 7.1
*/
public FieldBodyCenterPointing(final Frame inertialFrame, final Ellipsoid shape)
throws OrekitException {
super(inertialFrame, shape.getFrame());
this.ellipsoid = shape;
}
/** {@inheritDoc} */
public TimeStampedFieldPVCoordinates<T> getTargetPV(final FieldPVCoordinatesProvider<T> pvProv,
final FieldAbsoluteDate<T> date, final Frame frame)
throws OrekitException {
// spacecraft coordinates in body frame
final TimeStampedFieldPVCoordinates<T> scInBodyFrame = pvProv.getPVCoordinates(date, getBodyFrame());
// central projection to ground (NOT the classical nadir point)
final T u = scInBodyFrame.getPosition().getX().divide(ellipsoid.getA());
final T v = scInBodyFrame.getPosition().getY().divide(ellipsoid.getB());
final T w = scInBodyFrame.getPosition().getZ().divide(ellipsoid.getC());
final T d2 = u.pow(2).add(v.pow(2)).add(w.pow(2));
final T d = d2.sqrt();
final T ratio = d.pow(-1);
final FieldVector3D<T> projectedP = new FieldVector3D<T>(ratio, scInBodyFrame.getPosition());
// velocity
final T uDot = scInBodyFrame.getVelocity().getX().divide(ellipsoid.getA());
final T vDot = scInBodyFrame.getVelocity().getY().divide(ellipsoid.getB());
final T wDot = scInBodyFrame.getVelocity().getZ().divide(ellipsoid.getC());
//we aren't using the linearCombination in the library
final T dDot = (u.multiply(uDot).add(v.multiply(vDot)).add(w.multiply(wDot))).divide(d);
final T ratioDot = dDot.multiply(-1).divide(d2);
final FieldVector3D<T> projectedV = new FieldVector3D<T>(ratio, scInBodyFrame.getVelocity(),
ratioDot, scInBodyFrame.getPosition());
// acceleration
final T uDotDot = scInBodyFrame.getAcceleration().getX().divide(ellipsoid.getA());
final T vDotDot = scInBodyFrame.getAcceleration().getY().divide(ellipsoid.getB());
final T wDotDot = scInBodyFrame.getAcceleration().getZ().divide(ellipsoid.getC());
final T dDotDot = u.multiply(uDotDot).add(v.multiply(vDotDot)).add(w.multiply( wDotDot)
.add(uDot.pow(2).add(vDot.pow(2)).add(wDot.pow(2)).subtract(dDot.pow(2))))
.divide(d);
final T ratioDotDot = (dDot.pow(2).multiply(2).subtract(d.multiply(dDotDot))).divide(d.multiply(d2));
final FieldVector3D<T> projectedA = new FieldVector3D<T>(ratio, scInBodyFrame.getAcceleration(),
ratioDot.multiply(2), scInBodyFrame.getVelocity(),
ratioDotDot, scInBodyFrame.getPosition());
final TimeStampedFieldPVCoordinates<T> projected =
new TimeStampedFieldPVCoordinates<T>(date, projectedP, projectedV, projectedA);
return getBodyFrame().getTransformTo(frame, date.toAbsoluteDate()).transformPVCoordinates(projected);
}
}