Greetings everyone,
I have a Python code that finds the access times of a satellite to a FOV extending from a ground based station into the space. Setting up a proper frame for this FOV, one can use GroundFieldOfViewDetector to calculate these access times.
However, using this method we have a FOV infinitely extending into the space. Say, I want to limit my FOV’s space projection to 1000 km. Is this possible with any method that Orekit already has?
Thank you for the valuable discussion!
Kind regards,
Baris
Hi @Echulion,
You can wrap your GroundFieldOfViewDetector into an EventEnablingPredicateFilter with a custom EnablingPredicate to filter out events occurring beyond the maximum allowable distance between the spacecraft and the FOV location.
Hello @pascal.parraud,
Thank you for your reply and advice. Although what you propose sounds quite easy, I have no notion about how to implement this. So this is the class you’ve told me about:
EventEnablingPredicateFilter(T rawDetector, EnablingPredicate<? super T> enabler)
If I understood you correctly, rawDetector is supposed to be my GroundFieldOfViewDetector . And then I should set up my EnablingPredicate. It is as follows:
eventIsEnabled(SpacecraftState state, S eventDetector, double g)
so this also requires an event detector right? Though there isn’t one that calculates allowable distance between s/c and FOV events. This is the point where I am confused. Should I use something like FunctionalDetector as my custom event detector?
Thank you in advance for any further explanation and your time!
Hi @Echulion,
The following Java code for a class extending the EnablingPredicate interface is a suggestion that should meet your needs, under the assumption that the FoV is located at the origin of the linked frame:
class DistanceFilter implements EnablingPredicate {
private final double maxDistance;
public DistanceFilter(final double maxDistance) {
this.maxDistance = maxDistance;
}
public boolean eventIsEnabled(SpacecraftState s, EventDetector d, double g) {
Vector3D p = s.getPosition(((GroundFieldOfViewDetector)d).getFrame());
return p.getNorm() < maxDistance;
}
}
Since it looks like you’re using the Python wrapper, which I’m unfortunately not very familiar with, I guess you’ll have to implement the Python class PythonEnablingPredicate in a similar way, taking care to cast, in the eventIsEnabled method, the raw EventDetector to a GroundFieldOfViewDetector, casting being safe in this case.
The calling code (in Java, sorry) would be something like that:
FieldOfView fov = ...
Frame fovFrame = ... // a TopocentricFrame ?
GroundFieldOfViewDetector fovDetector =
new GroundFieldOfViewDetector(fovFrame, fov);
double maxDistance = 1000000.0; // 1000 km
EnablingPredicate predicate = new DistanceFilter(maxDistance);
propagator.addEventDetector(new EventEnablingPredicateFilter(fovDetector, predicate));