astromErrModel¶
-
lsst.validate.drp.astromerrmodel.
astromErrModel
(snr, theta=1000, sigmaSys=10, C=1)¶ Calculate expected astrometric uncertainty based on SNR.
mas = C*theta/SNR + sigmaSys
Parameters: - snr :
numpy.ndarray
orastropy.unit.Quantity
S/N of photometric measurements (dimensionless).
- theta :
float
,numpy.ndarray
orastropy.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
andsigmaSys
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.- snr :