/**
* 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);
}
/** {@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);
}
/**
* Creates new instance.
*
* @param shape Body shape
* @param attLaw Attitude law
* @param satPointingVector satellite vector defining the pointing direction
* @deprecated as of 7.1, replaced with {@link #LofOffsetPointing(Frame, BodyShape,
* AttitudeProvider, Vector3D)}
*/
@Deprecated
public LofOffsetPointing(
final BodyShape shape, final AttitudeProvider attLaw, final Vector3D satPointingVector) {
super(shape.getBodyFrame());
this.shape = shape;
this.attitudeLaw = attLaw;
this.satPointingVector = 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;
}
