astromErrModel¶

lsst.validate.drp.matchreduce.astromErrModel(snr, theta=1000, sigmaSys=10, C=1, **kwargs)[source]¶

Calculate expected astrometric uncertainty based on SNR.

mas = C*theta/SNR + sigmaSys

Parameters:

snr : list or numpy.array

S/N of photometric measurements

theta : float or numpy.array, optional

Seeing

sigmaSys : float

Systematic error floor

C : float

Scaling factor

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.

Returns:

np.array

Expected astrometric uncertainty. Units will be those of theta + sigmaSys.