/* 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 java.util.ArrayList;
import java.util.List;
import org.hipparchus.geometry.euclidean.threed.Line;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.Frame;
import org.orekit.frames.Transform;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.CartesianDerivativesFilter;
import org.orekit.utils.Constants;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedPVCoordinates;
/**
* This class provides a default attitude provider.
* <p>
* The attitude pointing law is defined by an attitude provider and
* the satellite axis vector chosen for pointing.
* <p>
* @author Véronique Pommier-Maurussane
*/
public class LofOffsetPointing extends GroundPointing {
/** Serializable UID. */
private static final long serialVersionUID = 20150529L;
/** Rotation from local orbital frame. */
private final AttitudeProvider attitudeLaw;
/** Body shape. */
private final BodyShape shape;
/** Chosen satellite axis for pointing, given in satellite frame. */
private final Vector3D satPointingVector;
/** Creates new instance.
* @param inertialFrame frame in which orbital velocities are computed
* @param shape Body shape
* @param attLaw Attitude law
* @param satPointingVector satellite vector defining the pointing direction
* @exception OrekitException if the frame specified is not a pseudo-inertial frame
* @since 7.1
*/
public LofOffsetPointing(final Frame inertialFrame, final BodyShape shape,
final AttitudeProvider attLaw, final Vector3D satPointingVector)
throws OrekitException {
super(inertialFrame, shape.getBodyFrame());
this.shape = shape;
this.attitudeLaw = attLaw;
this.satPointingVector = satPointingVector;
}
/** {@inheritDoc} */
@Override
public Attitude getAttitude(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame)
throws OrekitException {
return attitudeLaw.getAttitude(pvProv, date, frame);
}
/** {@inheritDoc} */
protected TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame)
throws OrekitException {
// transform from specified reference frame to spacecraft frame
final Transform refToSc =
new Transform(date,
new Transform(date, pvProv.getPVCoordinates(date, frame).negate()),
new Transform(date, attitudeLaw.getAttitude(pvProv, date, frame).getOrientation()));
// transform from specified reference frame to body frame
final Transform refToBody = frame.getTransformTo(shape.getBodyFrame(), date);
// sample intersection points in current date neighborhood
final Transform scToBody = new Transform(date, refToSc.getInverse(), refToBody);
final double h = 0.1;
final List<TimeStampedPVCoordinates> sample = new ArrayList<TimeStampedPVCoordinates>();
sample.add(losIntersectionWithBody(scToBody.shiftedBy(-h)));
sample.add(losIntersectionWithBody(scToBody));
sample.add(losIntersectionWithBody(scToBody.shiftedBy(+h)));
// use interpolation to compute properly the time-derivatives
final TimeStampedPVCoordinates targetBody =
TimeStampedPVCoordinates.interpolate(date, CartesianDerivativesFilter.USE_P, sample);
// convert back to caller specified frame
return refToBody.getInverse().transformPVCoordinates(targetBody);
}
/** Compute line of sight intersection with body.
* @param scToBody transform from spacecraft frame to body frame
* @return intersection point in body frame (only the position is set!)
* @exception OrekitException if line of sight does not intersect body
*/
private TimeStampedPVCoordinates losIntersectionWithBody(final Transform scToBody)
throws OrekitException {
// compute satellite pointing axis and position/velocity in body frame
final Vector3D pointingBodyFrame = scToBody.transformVector(satPointingVector);
final Vector3D pBodyFrame = scToBody.transformPosition(Vector3D.ZERO);
// Line from satellite following pointing direction
// we use arbitrarily the Earth radius as a scaling factor, it could be anything else
final Line pointingLine = new Line(pBodyFrame,
pBodyFrame.add(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
pointingBodyFrame),
1.0e-10);
// Intersection with body shape
final GeodeticPoint gpIntersection =
shape.getIntersectionPoint(pointingLine, pBodyFrame, shape.getBodyFrame(), scToBody.getDate());
final Vector3D pIntersection =
(gpIntersection == null) ? null : shape.transform(gpIntersection);
// Check there is an intersection and it is not in the reverse pointing direction
if ((pIntersection == null) ||
(Vector3D.dotProduct(pIntersection.subtract(pBodyFrame), pointingBodyFrame) < 0)) {
throw new OrekitException(OrekitMessages.ATTITUDE_POINTING_LAW_DOES_NOT_POINT_TO_GROUND);
}
return new TimeStampedPVCoordinates(scToBody.getDate(),
pIntersection, Vector3D.ZERO, Vector3D.ZERO);
}
}