Java tutorial
/* Copyright 2002-2015 CS Systmes d'Information * Licensed to CS Systmes 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.apache.commons.math3.geometry.euclidean.threed.Rotation; import org.apache.commons.math3.geometry.euclidean.threed.Vector3D; import org.apache.commons.math3.util.FastMath; import org.junit.Assert; import org.junit.Test; import org.orekit.Utils; import org.orekit.bodies.OneAxisEllipsoid; import org.orekit.errors.OrekitException; import org.orekit.frames.FramesFactory; import org.orekit.orbits.CircularOrbit; import org.orekit.propagation.analytical.EcksteinHechlerPropagator; import org.orekit.time.AbsoluteDate; import org.orekit.utils.AngularCoordinates; import org.orekit.utils.Constants; import org.orekit.utils.IERSConventions; import org.orekit.utils.PVCoordinates; public class AttitudeTest { @Test public void testZeroRate() throws OrekitException { Attitude attitude = new Attitude(AbsoluteDate.J2000_EPOCH, FramesFactory.getEME2000(), new Rotation(0.48, 0.64, 0.36, 0.48, false), Vector3D.ZERO, Vector3D.ZERO); Assert.assertEquals(Vector3D.ZERO, attitude.getSpin()); double dt = 10.0; Attitude shifted = attitude.shiftedBy(dt); Assert.assertEquals(Vector3D.ZERO, shifted.getRotationAcceleration()); Assert.assertEquals(Vector3D.ZERO, shifted.getSpin()); Assert.assertEquals(0.0, Rotation.distance(attitude.getRotation(), shifted.getRotation()), 1.0e-15); } @Test public void testShift() throws OrekitException { double rate = 2 * FastMath.PI / (12 * 60); Attitude attitude = new Attitude(AbsoluteDate.J2000_EPOCH, FramesFactory.getEME2000(), Rotation.IDENTITY, new Vector3D(rate, Vector3D.PLUS_K), Vector3D.ZERO); Assert.assertEquals(rate, attitude.getSpin().getNorm(), 1.0e-10); double dt = 10.0; double alpha = rate * dt; Attitude shifted = attitude.shiftedBy(dt); Assert.assertEquals(rate, shifted.getSpin().getNorm(), 1.0e-10); Assert.assertEquals(alpha, Rotation.distance(attitude.getRotation(), shifted.getRotation()), 1.0e-10); Vector3D xSat = shifted.getRotation().applyInverseTo(Vector3D.PLUS_I); Assert.assertEquals(0.0, xSat.subtract(new Vector3D(FastMath.cos(alpha), FastMath.sin(alpha), 0)).getNorm(), 1.0e-10); Vector3D ySat = shifted.getRotation().applyInverseTo(Vector3D.PLUS_J); Assert.assertEquals(0.0, ySat.subtract(new Vector3D(-FastMath.sin(alpha), FastMath.cos(alpha), 0)).getNorm(), 1.0e-10); Vector3D zSat = shifted.getRotation().applyInverseTo(Vector3D.PLUS_K); Assert.assertEquals(0.0, zSat.subtract(Vector3D.PLUS_K).getNorm(), 1.0e-10); } @Test public void testSpin() throws OrekitException { double rate = 2 * FastMath.PI / (12 * 60); Attitude attitude = new Attitude(AbsoluteDate.J2000_EPOCH, FramesFactory.getEME2000(), new Rotation(0.48, 0.64, 0.36, 0.48, false), new Vector3D(rate, Vector3D.PLUS_K), Vector3D.ZERO); Assert.assertEquals(rate, attitude.getSpin().getNorm(), 1.0e-10); double dt = 10.0; Attitude shifted = attitude.shiftedBy(dt); Assert.assertEquals(rate, shifted.getSpin().getNorm(), 1.0e-10); Assert.assertEquals(rate * dt, Rotation.distance(attitude.getRotation(), shifted.getRotation()), 1.0e-10); Vector3D shiftedX = shifted.getRotation().applyInverseTo(Vector3D.PLUS_I); Vector3D shiftedY = shifted.getRotation().applyInverseTo(Vector3D.PLUS_J); Vector3D shiftedZ = shifted.getRotation().applyInverseTo(Vector3D.PLUS_K); Vector3D originalX = attitude.getRotation().applyInverseTo(Vector3D.PLUS_I); Vector3D originalY = attitude.getRotation().applyInverseTo(Vector3D.PLUS_J); Vector3D originalZ = attitude.getRotation().applyInverseTo(Vector3D.PLUS_K); Assert.assertEquals(FastMath.cos(rate * dt), Vector3D.dotProduct(shiftedX, originalX), 1.0e-10); Assert.assertEquals(FastMath.sin(rate * dt), Vector3D.dotProduct(shiftedX, originalY), 1.0e-10); Assert.assertEquals(0.0, Vector3D.dotProduct(shiftedX, originalZ), 1.0e-10); Assert.assertEquals(-FastMath.sin(rate * dt), Vector3D.dotProduct(shiftedY, originalX), 1.0e-10); Assert.assertEquals(FastMath.cos(rate * dt), Vector3D.dotProduct(shiftedY, originalY), 1.0e-10); Assert.assertEquals(0.0, Vector3D.dotProduct(shiftedY, originalZ), 1.0e-10); Assert.assertEquals(0.0, Vector3D.dotProduct(shiftedZ, originalX), 1.0e-10); Assert.assertEquals(0.0, Vector3D.dotProduct(shiftedZ, originalY), 1.0e-10); Assert.assertEquals(1.0, Vector3D.dotProduct(shiftedZ, originalZ), 1.0e-10); Vector3D forward = AngularCoordinates.estimateRate(attitude.getRotation(), shifted.getRotation(), dt); Assert.assertEquals(0.0, forward.subtract(attitude.getSpin()).getNorm(), 1.0e-10); Vector3D reversed = AngularCoordinates.estimateRate(shifted.getRotation(), attitude.getRotation(), dt); Assert.assertEquals(0.0, reversed.add(attitude.getSpin()).getNorm(), 1.0e-10); } @Test public void testInterpolation() throws OrekitException { Utils.setDataRoot("regular-data"); final double ehMu = 3.9860047e14; final double ae = 6.378137e6; final double c20 = -1.08263e-3; final double c30 = 2.54e-6; final double c40 = 1.62e-6; final double c50 = 2.3e-7; final double c60 = -5.5e-7; final AbsoluteDate date = AbsoluteDate.J2000_EPOCH.shiftedBy(584.); final Vector3D position = new Vector3D(3220103., 69623., 6449822.); final Vector3D velocity = new Vector3D(6414.7, -2006., -3180.); final CircularOrbit initialOrbit = new CircularOrbit(new PVCoordinates(position, velocity), FramesFactory.getEME2000(), date, ehMu); EcksteinHechlerPropagator propagator = new EcksteinHechlerPropagator(initialOrbit, ae, ehMu, c20, c30, c40, c50, c60); OneAxisEllipsoid earth = new OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS, Constants.WGS84_EARTH_FLATTENING, FramesFactory.getITRF(IERSConventions.IERS_2010, true)); propagator.setAttitudeProvider(new BodyCenterPointing(initialOrbit.getFrame(), earth)); final Attitude initialAttitude = propagator.propagate(initialOrbit.getDate()).getAttitude(); // set up a 5 points sample List<Attitude> sample = new ArrayList<Attitude>(); for (double dt = 0; dt < 251.0; dt += 60.0) { sample.add(propagator.propagate(date.shiftedBy(dt)).getAttitude()); } // well inside the sample, interpolation should be better than quadratic shift double maxShiftAngleError = 0; double maxInterpolationAngleError = 0; double maxShiftRateError = 0; double maxInterpolationRateError = 0; for (double dt = 0; dt < 240.0; dt += 1.0) { AbsoluteDate t = initialOrbit.getDate().shiftedBy(dt); Attitude propagated = propagator.propagate(t).getAttitude(); double shiftAngleError = Rotation.distance(propagated.getRotation(), initialAttitude.shiftedBy(dt).getRotation()); double interpolationAngleError = Rotation.distance(propagated.getRotation(), initialAttitude.interpolate(t, sample).getRotation()); double shiftRateError = Vector3D.distance(propagated.getSpin(), initialAttitude.shiftedBy(dt).getSpin()); double interpolationRateError = Vector3D.distance(propagated.getSpin(), initialAttitude.interpolate(t, sample).getSpin()); maxShiftAngleError = FastMath.max(maxShiftAngleError, shiftAngleError); maxInterpolationAngleError = FastMath.max(maxInterpolationAngleError, interpolationAngleError); maxShiftRateError = FastMath.max(maxShiftRateError, shiftRateError); maxInterpolationRateError = FastMath.max(maxInterpolationRateError, interpolationRateError); } Assert.assertTrue(maxShiftAngleError > 4.0e-6); Assert.assertTrue(maxInterpolationAngleError < 1.5e-13); Assert.assertTrue(maxShiftRateError > 6.0e-8); Assert.assertTrue(maxInterpolationRateError < 2.5e-14); // past sample end, interpolation error should increase, but still be far better than quadratic shift maxShiftAngleError = 0; maxInterpolationAngleError = 0; maxShiftRateError = 0; maxInterpolationRateError = 0; for (double dt = 250.0; dt < 300.0; dt += 1.0) { AbsoluteDate t = initialOrbit.getDate().shiftedBy(dt); Attitude propagated = propagator.propagate(t).getAttitude(); double shiftAngleError = Rotation.distance(propagated.getRotation(), initialAttitude.shiftedBy(dt).getRotation()); double interpolationAngleError = Rotation.distance(propagated.getRotation(), initialAttitude.interpolate(t, sample).getRotation()); double shiftRateError = Vector3D.distance(propagated.getSpin(), initialAttitude.shiftedBy(dt).getSpin()); double interpolationRateError = Vector3D.distance(propagated.getSpin(), initialAttitude.interpolate(t, sample).getSpin()); maxShiftAngleError = FastMath.max(maxShiftAngleError, shiftAngleError); maxInterpolationAngleError = FastMath.max(maxInterpolationAngleError, interpolationAngleError); maxShiftRateError = FastMath.max(maxShiftRateError, shiftRateError); maxInterpolationRateError = FastMath.max(maxInterpolationRateError, interpolationRateError); } Assert.assertTrue(maxShiftAngleError > 9.0e-6); Assert.assertTrue(maxInterpolationAngleError < 6.0e-11); Assert.assertTrue(maxShiftRateError > 9.0e-8); Assert.assertTrue(maxInterpolationRateError < 4.0e-12); } }