Re: [Orekit Users] Issue with EventState/Propagator/Elevation Detector - HELP!!

["Ward, Evan" <Evan.Ward@nrl.navy.mil>]

Hi Jim,

Welcome to Orekit. 

On Mon, 2017-05-01 at 18:36 +0200, schatzman-james@n-ask.com wrote:

> The ElevationDetector mechanism discussed in the tutorial
>
> https://www.orekit.org/static/tutorial/propagation.html
>
> works fine for me, except for one thing. When I add multiple
> ElevationDetectors (wth different station locations and different
> EventHandlers) to the (Keplerian) propagator, the callbacks to eventOccurred
> in the EventHandler get mixed up. What I mean is that
>
> 1) Generally, the EventHandler associated with a given station location is
> called. GOOD
>
> 2) Sometimes, the EventHandler associated with the wrong station is called.
> For example, I set a threshold elevation of +10 degrees and most often the
> EventHandlers are called when the elevation is just about exactly +10, but
> sometimes an EventHandler is called when the elevation is -60 degrees to -30
> degrees. E.g., Station A is at +10 but the EventHandler for Station B is
> called. BAD

That is certainly a problem. Can you provide a short program that demonstrates the error, or better yet a failing JUnit test case? This will help us to understand exactly what is happening. What version of Orekit and Hipparchus are you using?

> Tracing through the call stack...
>
> Propagator.acceptStep  calls
>
> EventState.doEvent  calls
>
> AbstractDetector.eventOccurred  calls
>
> EventHandler.eventOccurred
>
> but it is the wrong detector (and wrong EventHandler).
>
> The EventState is a bit complicated and I don't really understand how this is
> supposed to work. What I want to be able to do is to propagate the orbit ONCE,
> flagging elevation events for ALL GROUND STATIONS. But obviously the code
> needs to know which stations trigger which events, and that it currently
> getting mixed up.

Your use case is certainly supported and one that users have had success with. If there is a problem with the code then it is certainly a bug that we would like to fix. 

Best Regards,

Evan

> Any suggestions?
>
> Thanks!
>
> Jim