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

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

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

> locOrbFrm object is referenced to another object.
>
> My main function code is:

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

[snip]


>             propS.addEventDetector(new CWAxisYDetector(initialOrbit,
> lof, initialDate));

[snip]


>                 SpacecraftState targ = prop.propagate(extrapDate);
>                 SpacecraftState inter = propS.propagate(extrapDate);
>                 PVCoordinates relst = inter.getPVCoordinates(lof);

It seems the numerical propagator "prop" is called simultaneously from  
various places:

  - directly from your code to compute targ
  - somewhere from the other "propS" propagator through CWAxisYDetector
    which in turn uses lof, which is based on "prop"
  - somewhere in lof to compute relst

As this propagator is a numerical one, it stores the final state after  
each call, so it is probably not safe to have it driven by so many  
different callers which will use it back and forth in time, and  
sometimes with zero size steps.

In order to compute relative position in a two-propagators setup, I  
would suggest to not use LocalOrbitalFrame but instead to compute  
directly the canonical vectors along the following lines (it is only a  
rough guess, I did not check if the vectors I compute here are the  
good ones):

 PVCoordinates relInert = new PVCoordinates(inter.getPVCoordinates(),
                                            targ.getPVCoordinates());
 Vector3D q = inter.getPVCoordinates().getPosition().normalize();
 Vector3D w = inter.getPVCoordinates().getMomentum().normalize();
 Vector3D s  = Vector3D.crossProduct(w, q);
 PVCoordinates relst =
    new PVCoordinates(new  
Vector3D(Vector3D.dotProduct(relInert.getPosition(), q),
                                    
Vector3D.dotProduct(relInert.getPosition(), s),
                                    
Vector3D.dotProduct(relInert.getPosition(), w)),
                      new  
Vector3D(Vector3D.dotProduct(relInert.getPosition(), q),
                                    
Vector3D.dotProduct(relInert.getPosition(), s),
                                    
Vector3D.dotProduct(relInert.getPosition(), w)));


Luc


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