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 org.apache.commons.math3.geometry.euclidean.threed.CardanEulerSingularityException; import org.apache.commons.math3.geometry.euclidean.threed.Rotation; import org.apache.commons.math3.geometry.euclidean.threed.RotationOrder; import org.apache.commons.math3.geometry.euclidean.threed.Vector3D; import org.apache.commons.math3.util.FastMath; import org.junit.After; import org.junit.Assert; import org.junit.Before; import org.junit.Test; import org.orekit.Utils; import org.orekit.bodies.GeodeticPoint; import org.orekit.bodies.OneAxisEllipsoid; import org.orekit.errors.OrekitException; import org.orekit.frames.Frame; import org.orekit.frames.FramesFactory; import org.orekit.frames.LOFType; import org.orekit.orbits.CircularOrbit; import org.orekit.orbits.KeplerianOrbit; import org.orekit.orbits.Orbit; import org.orekit.orbits.PositionAngle; import org.orekit.propagation.Propagator; import org.orekit.propagation.SpacecraftState; import org.orekit.propagation.analytical.KeplerianPropagator; import org.orekit.time.AbsoluteDate; import org.orekit.time.DateComponents; import org.orekit.time.TimeComponents; import org.orekit.time.TimeScalesFactory; import org.orekit.utils.AngularCoordinates; import org.orekit.utils.IERSConventions; import org.orekit.utils.PVCoordinates; public class LofOffsetTest { // Computation date private AbsoluteDate date; // Body mu private double mu; // Reference frame = ITRF 2005C private Frame itrf; // Earth shape OneAxisEllipsoid earthSpheric; // Satellite position CircularOrbit orbit; PVCoordinates pvSatEME2000; /** Test is the lof offset is the one expected */ @Test public void testZero() throws OrekitException, CardanEulerSingularityException { // Satellite position // Lof aligned attitude provider final LofOffset lofAlignedLaw = new LofOffset(orbit.getFrame(), LOFType.VVLH); final Rotation lofOffsetRot = lofAlignedLaw.getAttitude(orbit, date, orbit.getFrame()).getRotation(); // Check that final Vector3D momentumEME2000 = pvSatEME2000.getMomentum(); final Vector3D momentumLof = lofOffsetRot.applyTo(momentumEME2000); final double cosinus = FastMath.cos(Vector3D.dotProduct(momentumLof, Vector3D.PLUS_K)); Assert.assertEquals(1., cosinus, Utils.epsilonAngle); } /** Test if the lof offset is the one expected */ @Test public void testOffset() throws OrekitException, CardanEulerSingularityException { // Satellite position final CircularOrbit circ = new CircularOrbit(7178000.0, 0.5e-4, -0.5e-4, FastMath.toRadians(0.), FastMath.toRadians(270.), FastMath.toRadians(5.300), PositionAngle.MEAN, FramesFactory.getEME2000(), date, mu); // Create target pointing attitude provider // ************************************ // Elliptic earth shape final OneAxisEllipsoid earthShape = new OneAxisEllipsoid(6378136.460, 1 / 298.257222101, itrf); final GeodeticPoint geoTargetITRF2005 = new GeodeticPoint(FastMath.toRadians(43.36), FastMath.toRadians(1.26), 600.); // Attitude law definition from geodetic point target final TargetPointing targetLaw = new TargetPointing(circ.getFrame(), geoTargetITRF2005, earthShape); final Rotation targetRot = targetLaw.getAttitude(circ, date, circ.getFrame()).getRotation(); // Create lof aligned attitude provider // ******************************* final LofOffset lofAlignedLaw = new LofOffset(orbit.getFrame(), LOFType.VVLH); final Rotation lofAlignedRot = lofAlignedLaw.getAttitude(circ, date, circ.getFrame()).getRotation(); // Get rotation from LOF to target pointing attitude Rotation rollPitchYaw = targetRot.applyTo(lofAlignedRot.revert()).revert(); final double[] angles = rollPitchYaw.getAngles(RotationOrder.ZYX); final double yaw = angles[0]; final double pitch = angles[1]; final double roll = angles[2]; // Create lof offset attitude provider with computed roll, pitch, yaw // ************************************************************** final LofOffset lofOffsetLaw = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.ZYX, yaw, pitch, roll); final Rotation lofOffsetRot = lofOffsetLaw.getAttitude(circ, date, circ.getFrame()).getRotation(); // Compose rotations : target pointing attitudes final double angleCompo = targetRot.applyInverseTo(lofOffsetRot).getAngle(); Assert.assertEquals(0., angleCompo, Utils.epsilonAngle); } /** Test is the target pointed is the one expected */ @Test public void testTarget() throws OrekitException, CardanEulerSingularityException { // Create target point and target pointing law towards that point final GeodeticPoint targetDef = new GeodeticPoint(FastMath.toRadians(5.), FastMath.toRadians(-40.), 0.); final TargetPointing targetLaw = new TargetPointing(orbit.getFrame(), targetDef, earthSpheric); // Get roll, pitch, yaw angles corresponding to this pointing law final LofOffset lofAlignedLaw = new LofOffset(orbit.getFrame(), LOFType.VVLH); final Rotation lofAlignedRot = lofAlignedLaw.getAttitude(orbit, date, orbit.getFrame()).getRotation(); final Attitude targetAttitude = targetLaw.getAttitude(orbit, date, orbit.getFrame()); final Rotation rollPitchYaw = targetAttitude.getRotation().applyTo(lofAlignedRot.revert()).revert(); final double[] angles = rollPitchYaw.getAngles(RotationOrder.ZYX); final double yaw = angles[0]; final double pitch = angles[1]; final double roll = angles[2]; // Create a lof offset law from those values final LofOffset lofOffsetLaw = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.ZYX, yaw, pitch, roll); final LofOffsetPointing lofOffsetPtLaw = new LofOffsetPointing(orbit.getFrame(), earthSpheric, lofOffsetLaw, Vector3D.PLUS_K); // Check target pointed by this law : shall be the same as defined final Vector3D pTargetRes = lofOffsetPtLaw.getTargetPV(orbit, date, earthSpheric.getBodyFrame()) .getPosition(); final GeodeticPoint targetRes = earthSpheric.transform(pTargetRes, earthSpheric.getBodyFrame(), date); Assert.assertEquals(targetDef.getLongitude(), targetRes.getLongitude(), Utils.epsilonAngle); Assert.assertEquals(targetDef.getLongitude(), targetRes.getLongitude(), Utils.epsilonAngle); } @Test public void testSpin() throws OrekitException { final AttitudeProvider law = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.XYX, 0.1, 0.2, 0.3); AbsoluteDate date = new AbsoluteDate(new DateComponents(1970, 01, 01), new TimeComponents(3, 25, 45.6789), TimeScalesFactory.getUTC()); KeplerianOrbit orbit = new KeplerianOrbit(7178000.0, 1.e-4, FastMath.toRadians(50.), FastMath.toRadians(10.), FastMath.toRadians(20.), FastMath.toRadians(30.), PositionAngle.MEAN, FramesFactory.getEME2000(), date, 3.986004415e14); Propagator propagator = new KeplerianPropagator(orbit, law); double h = 0.01; SpacecraftState sMinus = propagator.propagate(date.shiftedBy(-h)); SpacecraftState s0 = propagator.propagate(date); SpacecraftState sPlus = propagator.propagate(date.shiftedBy(h)); // check spin is consistent with attitude evolution double errorAngleMinus = Rotation.distance(sMinus.shiftedBy(h).getAttitude().getRotation(), s0.getAttitude().getRotation()); double evolutionAngleMinus = Rotation.distance(sMinus.getAttitude().getRotation(), s0.getAttitude().getRotation()); Assert.assertEquals(0.0, errorAngleMinus, 1.0e-6 * evolutionAngleMinus); double errorAnglePlus = Rotation.distance(s0.getAttitude().getRotation(), sPlus.shiftedBy(-h).getAttitude().getRotation()); double evolutionAnglePlus = Rotation.distance(s0.getAttitude().getRotation(), sPlus.getAttitude().getRotation()); Assert.assertEquals(0.0, errorAnglePlus, 1.0e-6 * evolutionAnglePlus); Vector3D spin0 = s0.getAttitude().getSpin(); Vector3D reference = AngularCoordinates.estimateRate(sMinus.getAttitude().getRotation(), sPlus.getAttitude().getRotation(), 2 * h); Assert.assertEquals(0.0, spin0.subtract(reference).getNorm(), 1.0e-10); } @Test public void testAnglesSign() throws OrekitException { AbsoluteDate date = new AbsoluteDate(new DateComponents(1970, 01, 01), new TimeComponents(3, 25, 45.6789), TimeScalesFactory.getUTC()); KeplerianOrbit orbit = new KeplerianOrbit(7178000.0, 1.e-8, FastMath.toRadians(50.), FastMath.toRadians(10.), FastMath.toRadians(20.), FastMath.toRadians(0.), PositionAngle.MEAN, FramesFactory.getEME2000(), date, 3.986004415e14); double alpha = 0.1; double cos = FastMath.cos(alpha); double sin = FastMath.sin(alpha); // Roll Attitude attitude = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.XYZ, alpha, 0.0, 0.0) .getAttitude(orbit, date, orbit.getFrame()); checkSatVector(orbit, attitude, Vector3D.PLUS_I, 1.0, 0.0, 0.0, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_J, 0.0, cos, sin, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_K, 0.0, -sin, cos, 1.0e-8); // Pitch attitude = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.XYZ, 0.0, alpha, 0.0) .getAttitude(orbit, date, orbit.getFrame()); checkSatVector(orbit, attitude, Vector3D.PLUS_I, cos, 0.0, -sin, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_J, 0.0, 1.0, 0.0, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_K, sin, 0.0, cos, 1.0e-8); // Yaw attitude = new LofOffset(orbit.getFrame(), LOFType.VVLH, RotationOrder.XYZ, 0.0, 0.0, alpha) .getAttitude(orbit, date, orbit.getFrame()); checkSatVector(orbit, attitude, Vector3D.PLUS_I, cos, sin, 0.0, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_J, -sin, cos, 0.0, 1.0e-8); checkSatVector(orbit, attitude, Vector3D.PLUS_K, 0.0, 0.0, 1.0, 1.0e-8); } @Test public void testRetrieveAngles() throws OrekitException, CardanEulerSingularityException { AbsoluteDate date = new AbsoluteDate(new DateComponents(1970, 01, 01), new TimeComponents(3, 25, 45.6789), TimeScalesFactory.getUTC()); KeplerianOrbit orbit = new KeplerianOrbit(7178000.0, 1.e-4, FastMath.toRadians(50.), FastMath.toRadians(10.), FastMath.toRadians(20.), FastMath.toRadians(30.), PositionAngle.MEAN, FramesFactory.getEME2000(), date, 3.986004415e14); RotationOrder order = RotationOrder.ZXY; double alpha1 = 0.123; double alpha2 = 0.456; double alpha3 = 0.789; LofOffset law = new LofOffset(orbit.getFrame(), LOFType.VVLH, order, alpha1, alpha2, alpha3); Rotation offsetAtt = law.getAttitude(orbit, date, orbit.getFrame()).getRotation(); Rotation alignedAtt = new LofOffset(orbit.getFrame(), LOFType.VVLH) .getAttitude(orbit, date, orbit.getFrame()).getRotation(); Rotation offsetProper = offsetAtt.applyTo(alignedAtt.revert()); double[] angles = offsetProper.revert().getAngles(order); Assert.assertEquals(alpha1, angles[0], 1.0e-11); Assert.assertEquals(alpha2, angles[1], 1.0e-11); Assert.assertEquals(alpha3, angles[2], 1.0e-11); } private void checkSatVector(Orbit o, Attitude a, Vector3D satVector, double expectedX, double expectedY, double expectedZ, double threshold) { Vector3D zLof = o.getPVCoordinates().getPosition().normalize().negate(); Vector3D yLof = o.getPVCoordinates().getMomentum().normalize().negate(); Vector3D xLof = Vector3D.crossProduct(yLof, zLof); Assert.assertTrue(Vector3D.dotProduct(xLof, o.getPVCoordinates().getVelocity()) > 0); Vector3D v = a.getRotation().applyInverseTo(satVector); Assert.assertEquals(expectedX, Vector3D.dotProduct(v, xLof), 1.0e-8); Assert.assertEquals(expectedY, Vector3D.dotProduct(v, yLof), 1.0e-8); Assert.assertEquals(expectedZ, Vector3D.dotProduct(v, zLof), 1.0e-8); } @Before public void setUp() { try { Utils.setDataRoot("regular-data"); // Computation date date = new AbsoluteDate(new DateComponents(2008, 04, 07), TimeComponents.H00, TimeScalesFactory.getUTC()); // Body mu mu = 3.9860047e14; // Reference frame = ITRF 2005 itrf = FramesFactory.getITRF(IERSConventions.IERS_2010, true); // Elliptic earth shape earthSpheric = new OneAxisEllipsoid(6378136.460, 0., itrf); // Satellite position orbit = new CircularOrbit(7178000.0, 0.5e-8, -0.5e-8, FastMath.toRadians(50.), FastMath.toRadians(150.), FastMath.toRadians(5.300), PositionAngle.MEAN, FramesFactory.getEME2000(), date, mu); pvSatEME2000 = orbit.getPVCoordinates(); } catch (OrekitException oe) { Assert.fail(oe.getMessage()); } } @After public void tearDown() { date = null; itrf = null; earthSpheric = null; } }