astromErrModel

lsst.validate.drp.astromerrmodel.astromErrModel(snr, theta=1000, sigmaSys=10, C=1, **kwargs)

Calculate expected astrometric uncertainty based on SNR.

mas = C*theta/SNR + sigmaSys

Parameters:

snr : numpy.ndarray or astropy.unit.Quantity

S/N of photometric measurements (dimensionless).

theta : float, numpy.ndarray or astropy.unit.Quantity, optional

Seeing (default: milliarcsec).

sigmaSys : astropy.unit.Quantity

Systematic error floor (default: milliarcsec).

C : float

Scaling factor (dimensionless)

Returns:

sigma : astropy.unit.Quantity

Expected astrometric uncertainty with the same dimensions as snr. Units will be those of theta and sigmaSys.

Notes

theta and sigmaSys must be given in the same units. Typically choices might be any of arcsec, milli-arcsec, or radians. The default values are reasonable astronominal values in milliarcsec. But the only thing that matters is that they’re the same.