Correlated Random Vector Generator covariance matrix

[eliemaz]

Hello.

To generate measurements, I use an AngularRaDecBuilder with a noise source represented by a CorrelatedRandomVectorGenerator. If I define a diagonal covariance matrix as an argument, then I expect to have independent but individually noisy measurements. However, what do these diagonal coefficients of my matrix represent? Do they represent an error in my 3D position or directly an error in my observable quantities (RA and Dec in my case)?

What should be the unit of sigma in that case?

GaussGenerator = GaussianRandomGenerator(JDKRandomGenerator())
diag = DiagonalMatrix([sigma**2 for _ in range(len(list_dates))])
crvg = CorrelatedRandomVectorGenerator(diag, 1.0e-10, GaussGenerator)
ra_dec_builder = AngularRaDecBuilder(crvg, self.groundstation, self.inertialframe, [1.0, 1.0], [1.0, 1.0], self.dummysatellite)

Best regards.

[MaximeJ]

Hi @eliemaz,

@eliemaz

However, what do these diagonal coefficients of my matrix represent? Do they represent an error in my 3D position or directly an error in my observable quantities (RA and Dec in my case)?

“directly an error in my observable quantities” → this is the covariance matrix of the measurements, if purely diagonal it will apply a Gaussian error with STD \sigma_{RA} on the right-ascension and \sigma_{DEC} on the declination.

@eliemaz

What should be the unit of sigma in that case?

Radians, as a general rule all units used by Orekit are in SI.

Best regards,
Maxime