Detecting elevation inside range

Orekit usage
1

Hi,
I’m trying to combine two elevation detectors to detect events when the elevation of a spacecraft falls into a certain range [low, high]. E1 is an ElevationDetector with const elevation high, and E2 is an ElevationDetector with const elevation low.
Tried to combine them using andCombine([E2, notCombine(E1)]). Should this work?

BTW, I’m pleased with all the help you have provided in these formus.

2

Hello @5tardust,

This should Indeed do the trick ! Just be careful with the “maxCheck” setting as your combined detector could miss the event if the range is small.

We are happy to help :+1:

Cheers,
Vincent

3

Hi there,

Note that combining detectors is not performant in the sense that elevation will be computed twice (might not be a problem for your application). You could create your own detector with g like that:
g = (el - el_min) * (el - el_max)
You can check out in ElevationDetector how the elevation is obtained from the state.

Cheers,
Romain.

2 Likes
4

Sorry about the delay in my response.

detectors = [ElevationDetector(frame).
                 withConstantElevation(radians(15)),
                 BooleanDetector.notCombine(
                 ElevationDetector(frame).
                 withConstantElevation(radians(40)))]
ba = BooleanDetector.andCombine(detectors).withHandler(gs)

This did not work, the second elevation detector had no effect. However,

ba = Elevation2Detector(frame, (15, 40))

… did, with Elevation2Detector being a custom detector with g() function:

def g(self, state: SpacecraftState):
        el = self._frame.getElevation(state.getPosition(), state.getFrame(),
                                      state.getDate())
        return (el - self._el_minmax[0]) * (self._el_minmax[1] - el)
5

Update. It seems that my custom detector causes orekit to enter a live-lock. Added some debugging since my program sometimes seemed to hang. I discovered that orekit enters an endless loop of calling the g() function above with various states.

Any inkling about the reason for this?

Thanks.

6

Hi,

Whare are the settings you pass to the detector ?
I mean threshold, etc.

Cheers,
Romain.

7 
        super().__init__(float(time_step),
                         PythonAbstractDetector.DEFAULT_THRESHOLD,
                         PythonAbstractDetector.DEFAULT_MAX_ITER,
                         handler)

Time step is 10

One twist is that this detector runs in an chain like this:

BooleanDetector.andCombine([Elevation2Detector(...)]).withHandler(ehandler)

This happend regardless if andCombine list only contains the Elevation2Detector or additional detectors.

Is there a potential problem in that I reuse the propagator with different detectors? I.e. using clearEventsDetectors() then addEventDetector()?

Regards,
Nils

8

It seems that I was wrong in assuming a live lock. Please ignore my last two comments.
Regards

1 Like