build_astrometric_error_model

lsst.validate.drp.astromerrmodel.build_astrometric_error_model(matchedMultiVisitDataset, selection, medianRef=100, matchRef=500)

Serializable model of astrometry errors across multiple visits.

\[\mathrm{astromRms} = C \theta / \mathrm{SNR} + \sigma_\mathrm{sys}\]
Parameters:
matchedMultiVisitDataset : MatchedMultiVisitDataset

A dataset containing matched statistics for stars across multiple visits.

selection : np.array of bool

The selection of sources to use to build the model.

medianRef : float or astropy.unit.Quantity, optional

Median reference astrometric scatter (default: milliarcsecond).

matchRef : int, optional

Should match at least matchRef number of stars (dimensionless).
Returns:
blob : lsst.verify.Blob

Blob with datums:

  • C: Model scaling factor.
  • theta: Seeing (milliarcsecond).
  • sigmaSys: Systematic error floor (milliarcsecond).
  • astromRms: Astrometric scatter (RMS) for good stars (milliarcsecond).

Notes

The scatter and match defaults appropriate to SDSS are the defaults for medianRef and matchRef.

For SDSS, stars with mag < 19.5 should be completely well measured.