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Re: [Orekit Users] My EventDetector class can't correct detecting event?

beowulf zhang <beowulf.zhang@gmail.com> a écrit :

what I finded in my app is that the EventDetector.threshold is
sensitive, if the value is improper set, and the result is error.

Yes, this is a sensitive parameter. Also take care not to mix the threshold and the maxCheck parameters.

Threshold is a convergence parameter, it corresponds to the final accuracy at which you want your event to be located in time. It is often between 1.0e-3 (i.e one millisecond) for physical meaningful value and 1.0e-10 if you want reproducible results for regression tests, despite the physical meaning is dubious at this low level. Using a value about 1.0e-13 or even below would be really hasardous as the representation of dates is limited by double precision.

MaxCheck is only used has to avoid sampling the event g function too much in a bracketing phase before starting to find a root. So the meaning of this value is essentially to avoid missing two close successive roots, as we may not see the function becomes negative between them, if we don't sample between them. As an example, if your g function represents an eclipse, setting this value to 60 seconds would mean you may miss eclipses shorter than 60 s. So this value is often set to a rather high value (of the order of magnitude of minutes or even hours for some very low frequency events).


2011/6/4, beowulf zhang <beowulf.zhang@gmail.com>:
I see, Thank You!

2011/6/4, MAISONOBE Luc <luc.maisonobe@c-s.fr>:
beowulf zhang <beowulf.zhang@gmail.com> a écrit :

I finded that the integrator called the class CombinedEventsManager
and EventState of the common-math, not those in the orekit5. why?

The NumericalPropagator in Orekit delegates everything to Apache
Commons Math, including events and step handling. It only add wrappers
to convert between the low level double arrays Apache Commons Math
uses and the higher level SpacecraftState and AbsoluteDate Orekit uses.

The EventState class from Orekit is used by the non-numerical (i.e.
analytical) propagtors, since they do not rely on any service provided
by Apache Commons Math. The CombinedEventsDetectorsManager class is
obsolete and is not used anymore, we should remove it.


2011/5/31, beowulf zhang <beowulf.zhang@gmail.com>:
I find recursive in debug, stack is:

double, double[], double, double[]) line: 172
NumericalPropagator.propagate(AbsoluteDate) line: 419
NumericalPropagator.getPVCoordinates(AbsoluteDate, Frame) line: 462
LocalOrbitalFrame.updateFrame(AbsoluteDate) line: 81
EME2000Frame(Frame).getTransformTo(Frame, AbsoluteDate) line: 201
EquinoctialOrbit(Orbit).getPVCoordinates(Frame) line: 240
SpacecraftState.getPVCoordinates(Frame) line: 361
CWAxisYDetector.g(SpacecraftState) line: 37
AdaptedEventDetector.g(double, double[]) line: 74
EventState.reinitializeBegin(double, double[]) line: 152
CombinedEventsManager.evaluateStep(StepInterpolator) line: 142
double, double[], double, double[]) line: 172
NumericalPropagator.propagate(AbsoluteDate) line: 419
SlaveMode.main(String[]) line: 138

Maybe this is a debug!

2011/5/31, beowulf zhang <beowulf.zhang@gmail.com>:
locOrbFrm object is referenced to another object.

My main function code is:

            // configure Orekit

            // Initial orbit parameters
            double a = 7396159; // semi major axis in meters
            double e = 0.001; // eccentricity
            double i = Math.toRadians(7); // inclination
            double omega = Math.toRadians(180); // perigee argument
            double raan = Math.toRadians(261); // right ascension of
ascending node
            double lM = 0; // mean anomaly

            // Inertial frame
            Frame inertialFrame = FramesFactory.getEME2000();

            // Initial date in UTC time scale
            TimeScale utc = TimeScalesFactory.getUTC();
            AbsoluteDate initialDate = new AbsoluteDate(2004, 01, 01,
23, 30, 00.000, utc);

            // gravitation coefficient
            double mu =  3.986004415e+14;

            // Orbit construction as Keplerian
            Orbit initialOrbit = new KeplerianOrbit(a, e, i, omega,

initialDate, mu);

            // Simple extrapolation with Keplerian motion
            //KeplerianPropagator kepler = new
            double stepSize = 9;  // the step is ten seconds
            FirstOrderIntegrator integrator = new
            NumericalPropagator prop = new
            SpacecraftState initialState = new

            // Set the propagator to slave mode (could be omitted as
it is the default mode)

            // 生成目标当地轨道系
            LocalOrbitalFrame lof = new
LocalOrbitalFrame(inertialFrame, LOFType.QSW, prop, "LOF");

            // 根据相对状态构造追踪星
            PVCoordinates relSt = new PVCoordinates(new
            										new Vector3D(0.0,1.0,0.0));
            PVCoordinates initPV = lof.getTransformTo(inertialFrame,

            // Simple extrapolation with Keplerian motion
            //KeplerianPropagator kepler = new
            FirstOrderIntegrator integratorS = new
            NumericalPropagator propS = new
            SpacecraftState initialStateS = new SpacecraftState(new
            		inertialFrame, initialDate, mu));

            // Set the propagator to slave mode (could be omitted as
it is the default mode)
            propS.addEventDetector(new CWAxisYDetector(initialOrbit,
lof, initialDate));

            // Overall duration in seconds for extrapolation
            double duration = initialOrbit.getKeplerianPeriod() * 2.0;

            PrintWriter relFile = null;
            try {
				relFile = new PrintWriter("relst.txt");
			} catch (FileNotFoundException e1) {

            // Stop date
            final AbsoluteDate finalDate =  new
AbsoluteDate(initialDate, duration, utc);

            // Extrapolation loop
            boolean first = true;
            AbsoluteDate extrapDate = initialDate;
            while (extrapDate.compareTo(finalDate) <= 0)  {

                SpacecraftState targ = prop.propagate(extrapDate);
                SpacecraftState inter = propS.propagate(extrapDate);
                PVCoordinates relst = inter.getPVCoordinates(lof);
                double tm = extrapDate.durationFrom(initialDate);
                relFile.printf("%f %f %f %f\n",
                		tm, relst.getPosition().getX(),
relst.getPosition().getY(), relst.getPosition().getZ());

                extrapDate = new AbsoluteDate(extrapDate, stepSize,

            System.out.println("The End");

2011/5/31, MAISONOBE Luc <luc.maisonobe@c-s.fr>:
beowulf zhang <beowulf.zhang@gmail.com> a écrit :

I write a class CWAxisYDetector derived from AbstractDetector, the

public class CWAxisYDetector extends AbstractDetector {

	private LocalOrbitalFrame locOrbFrm;

	private AbsoluteDate initDate;

	protected CWAxisYDetector(Orbit targOrb, LocalOrbitalFrame lof,
AbsoluteDate iDate) {
		super(targOrb.getKeplerianPeriod() / 3, 1.0e-13 *
		this.locOrbFrm = lof;
		this.initDate = iDate;

	public int eventOccurred(SpacecraftState s, boolean increasing)
			throws OrekitException {
		return CONTINUE;

	public double g(SpacecraftState s) throws OrekitException {
		return s.getPVCoordinates(locOrbFrm).getPosition().getX();

If the local orbital frame here is linked to the same spacecraft
orbit is propagated, then
s.getPVCoordinates(locOrbFrm).getPosition().getX() should always be 0
(as well as Y and Z since the spacecraft defines the origin of this
So the function is essentially an observation of numerical errors in
interpolation polynomials, it is not a function that clearly crosses
the zero axis at one precise time.

Are you sure about the frame ? Shouldn't it be related to another
spacecraft (for relative motion observation for example) ?



but this class can't correct detecting event, and in some integrate
step getinig error information:

Exception in thread "main"
org.apache.commons.math.MathRuntimeException$4: function values at
endpoints do not have different signs.  Endpoints: [0.539, 0.539],
Values: [0, 0]
	at fr.cs.examples.propagation.SlaveMode.main(SlaveMode.java:136)


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