Simulations of observations

[MaximeJ]

Hi @jlipinski,

@jlipinski

Now I can’t really figure out how to define DoubleDihedralFieldOfView. Lets say I have a camera with X degrees width and Y degrees height with its center pointing at 180 degrees AZ and 45 degrees EL. Can’t really figure out how to transform this coordinates and numbers in horizontal reference system to Vector3D.

TopocentricFrame are defined with:

• X axis in the local horizontal plane (normal to zenith direction) and following the local parallel towards East;
• Y axis in the horizontal plane (normal to zenith direction) and following the local meridian towards North;
• Z axis towards Zenith direction.

By convention azimuth is counted clockwise from the North direction, so positive towards the East (see TopocentricFrame#getAzimuth).

Given the arguments of the constructor of DoubleDihedralFieldOfView:

• center vector, in your case (AZ, EL) = (180°, 45°) should give you : center = [0, -\sqrt(2)/2, \sqrt(2)/2]
• axis1 and axis2: depends on how your sensor is rotated around the direction of the FOV center.
  If you want one of the side to be parallel to the local horizontal, you can choose axis1 = [1, 0, 0]
  Axis2 will be perpendicular to the 2 previous vector: axis2 = [0, \sqrt(2)/2, \sqrt(2)/2]
• halfAperture1, halfAperture2: half aperture (in radians) of your FOV along each axis
• margin can be set to 0.

@jlipinski

Additionally, is this method detects only visible satellites, i.e. not in Earth umbra or do I need to implement another method to detect if satellite is in umbra.

You have to add another detector for this.

@jlipinski

Moreover is there a simple way to detect only after civil dusk and before civil dawn, like check if in location of detector Sun is more than 6 degrees below the horizon?

The GroundAtNightDetector with CIVIL_DAWN_DUSK_ELEVATION (you can ignore atmospheric refraction to begin with).
The g detection function is positive when the ground is at night:

CelestialBody sun = CelestialBodyFactory.getSun();
GroundAtNightDetector nightDetector = new GroundAtNightDetector(stationFrame, sun, GroundAtNightDetector.CIVIL_DAWN_DUSK_ELEVATION, null);

Then you want to combine both detectors, using a BooleanDetector.
The andCombine g function is positive if and only if the g functions of all detectors are positive.
However the GoundFieldOfView detector g function is negative when the object is in the FOV, you’ll need to negate that.
In the end, you will have:

BooleanDetector fovAtNightDetector = BooleanDetector.andCombine(BooleanDetector.notCombine(fovGroundDetector), nightDetector);

There is probably a more elegant way to do this using an EventEnablingPredicateFilter but I’m not sure how to do it right now, I’ll think about it when I have more time.

Hope this helps,
Maxime