Java tutorial
/* Copyright 2002-2010 CS Communication & Systmes * Licensed to CS Communication & Systmes (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.frames; import org.apache.commons.math.geometry.Rotation; import org.apache.commons.math.geometry.Vector3D; import org.orekit.errors.OrekitException; import org.orekit.time.AbsoluteDate; import org.orekit.utils.Constants; /** Mean Equator, Mean Equinox Frame. * <p>This frame handles precession effects according to the IAU-76 model (Lieske).</p> * <p>Its parent frame is the GCRF frame.<p> * <p>It is sometimes called Mean of Date (MoD) frame.<p> * @author Pascal Parraud * @version $Revision$ $Date$ */ class MEMEFrame extends Frame { /** Serializable UID. */ private static final long serialVersionUID = -4939175733381713275L; /** Radians per arcsecond. */ private static final double RADIANS_PER_ARC_SECOND = Math.PI / (180.0 * 3600.0); /** 1st coefficient for ZETA precession angle. */ private static final double ZETA_1 = 2306.2181 * RADIANS_PER_ARC_SECOND; /** 2nd coefficient for ZETA precession angle. */ private static final double ZETA_2 = 0.30188 * RADIANS_PER_ARC_SECOND; /** 3rd coefficient for ZETA precession angle. */ private static final double ZETA_3 = 0.017998 * RADIANS_PER_ARC_SECOND; /** 1st coefficient for THETA precession angle. */ private static final double THETA_1 = 2004.3109 * RADIANS_PER_ARC_SECOND; /** 2nd coefficient for THETA precession angle. */ private static final double THETA_2 = -0.42665 * RADIANS_PER_ARC_SECOND; /** 3rd coefficient for THETA precession angle. */ private static final double THETA_3 = -0.041833 * RADIANS_PER_ARC_SECOND; /** 1st coefficient for Z precession angle. */ private static final double Z_1 = 2306.2181 * RADIANS_PER_ARC_SECOND; /** 2nd coefficient for Z precession angle. */ private static final double Z_2 = 1.09468 * RADIANS_PER_ARC_SECOND; /** 3rd coefficient for Z precession angle. */ private static final double Z_3 = 0.018203 * RADIANS_PER_ARC_SECOND; /** Cached date to avoid useless computation. */ private AbsoluteDate cachedDate; /** Simple constructor, applying EOP corrections (here, EME2000/GCRF bias compensation). * @param date the date. * @param name name of the frame * @exception OrekitException if EOP parameters cannot be read */ protected MEMEFrame(final AbsoluteDate date, final String name) throws OrekitException { this(true, date, name); } /** Simple constructor. * @param applyEOPCorr if true, EOP correction is applied (here, EME2000/GCRF bias compensation) * @param date the date. * @param name name of the frame * @exception OrekitException if EOP parameters are desired but cannot be read */ protected MEMEFrame(final boolean applyEOPCorr, final AbsoluteDate date, final String name) throws OrekitException { super(applyEOPCorr ? FramesFactory.getGCRF() : FramesFactory.getEME2000(), null, name, true); // everything is in place, we can now synchronize the frame updateFrame(date); } /** Update the frame to the given date. * <p>The update considers the precession effects.</p> * @param date new value of the date */ protected void updateFrame(final AbsoluteDate date) { if ((cachedDate == null) || !cachedDate.equals(date)) { // offset from J2000 epoch in julian centuries final double tts = date.durationFrom(AbsoluteDate.J2000_EPOCH); final double ttc = tts / Constants.JULIAN_CENTURY; // compute the zeta precession angle final double zeta = ((ZETA_3 * ttc + ZETA_2) * ttc + ZETA_1) * ttc; // compute the theta precession angle final double theta = ((THETA_3 * ttc + THETA_2) * ttc + THETA_1) * ttc; // compute the z precession angle final double z = ((Z_3 * ttc + Z_2) * ttc + Z_1) * ttc; // elementary rotations for precession final Rotation r1 = new Rotation(Vector3D.PLUS_K, z); final Rotation r2 = new Rotation(Vector3D.PLUS_J, -theta); final Rotation r3 = new Rotation(Vector3D.PLUS_K, zeta); // complete precession final Rotation precession = r1.applyTo(r2.applyTo(r3)); // set up the transform from parent GCRF setTransform(new Transform(precession)); cachedDate = date; } } }