BodyCenterPointing.java
- /* Copyright 2002-2020 CS GROUP
- * Licensed to CS GROUP (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.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.hipparchus.util.FastMath;
- import org.hipparchus.util.MathArrays;
- import org.orekit.bodies.Ellipsoid;
- import org.orekit.frames.Frame;
- import org.orekit.time.AbsoluteDate;
- import org.orekit.time.FieldAbsoluteDate;
- import org.orekit.utils.FieldPVCoordinatesProvider;
- import org.orekit.utils.PVCoordinatesProvider;
- import org.orekit.utils.TimeStampedFieldPVCoordinates;
- import org.orekit.utils.TimeStampedPVCoordinates;
- /**
- * 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 BodyCenterPointing extends GroundPointing {
- /** Body ellipsoid. */
- private final Ellipsoid ellipsoid;
- /** Creates new instance.
- * @param inertialFrame frame in which orbital velocities are computed
- * @param shape Body shape
- * @since 7.1
- */
- public BodyCenterPointing(final Frame inertialFrame, final Ellipsoid shape) {
- super(inertialFrame, shape.getFrame());
- this.ellipsoid = shape;
- }
- /** {@inheritDoc} */
- @Override
- public TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
- final AbsoluteDate date, final Frame frame) {
- // spacecraft coordinates in body frame
- final TimeStampedPVCoordinates scInBodyFrame = pvProv.getPVCoordinates(date, getBodyFrame());
- // central projection to ground (NOT the classical nadir point)
- final double u = scInBodyFrame.getPosition().getX() / ellipsoid.getA();
- final double v = scInBodyFrame.getPosition().getY() / ellipsoid.getB();
- final double w = scInBodyFrame.getPosition().getZ() / ellipsoid.getC();
- final double d2 = u * u + v * v + w * w;
- final double d = FastMath.sqrt(d2);
- final double ratio = 1.0 / d;
- final Vector3D projectedP = new Vector3D(ratio, scInBodyFrame.getPosition());
- // velocity
- final double uDot = scInBodyFrame.getVelocity().getX() / ellipsoid.getA();
- final double vDot = scInBodyFrame.getVelocity().getY() / ellipsoid.getB();
- final double wDot = scInBodyFrame.getVelocity().getZ() / ellipsoid.getC();
- final double dDot = MathArrays.linearCombination(u, uDot, v, vDot, w, wDot) / d;
- final double ratioDot = -dDot / d2;
- final Vector3D projectedV = new Vector3D(ratio, scInBodyFrame.getVelocity(),
- ratioDot, scInBodyFrame.getPosition());
- // acceleration
- final double uDotDot = scInBodyFrame.getAcceleration().getX() / ellipsoid.getA();
- final double vDotDot = scInBodyFrame.getAcceleration().getY() / ellipsoid.getB();
- final double wDotDot = scInBodyFrame.getAcceleration().getZ() / ellipsoid.getC();
- final double dDotDot = (MathArrays.linearCombination(u, uDotDot, v, vDotDot, w, wDotDot) +
- uDot * uDot + vDot * vDot + wDot * wDot - dDot * dDot) / d;
- final double ratioDotDot = (2 * dDot * dDot - d * dDotDot) / (d * d2);
- final Vector3D projectedA = new Vector3D(ratio, scInBodyFrame.getAcceleration(),
- 2 * ratioDot, scInBodyFrame.getVelocity(),
- ratioDotDot, scInBodyFrame.getPosition());
- final TimeStampedPVCoordinates projected =
- new TimeStampedPVCoordinates(date, projectedP, projectedV, projectedA);
- return getBodyFrame().getTransformTo(frame, date).transformPVCoordinates(projected);
- }
- /** {@inheritDoc} */
- public <T extends RealFieldElement<T>> TimeStampedFieldPVCoordinates<T> getTargetPV(final FieldPVCoordinatesProvider<T> pvProv,
- final FieldAbsoluteDate<T> date, final Frame frame) {
- // 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.reciprocal();
- final FieldVector3D<T> projectedP = new FieldVector3D<>(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<>(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<>(ratio, scInBodyFrame.getAcceleration(),
- ratioDot.multiply(2), scInBodyFrame.getVelocity(),
- ratioDotDot, scInBodyFrame.getPosition());
- final TimeStampedFieldPVCoordinates<T> projected =
- new TimeStampedFieldPVCoordinates<>(date, projectedP, projectedV, projectedA);
- return getBodyFrame().getTransformTo(frame, date.toAbsoluteDate()).transformPVCoordinates(projected);
- }
- }