Summary: For the LSF and PSF calibration in the Gaia IDT/IDU we need LSF/PSF models that are both accurate and have as few free parameters as possible. General-purpose functions such as splines are not the best choice since they tend to require more parameters than strictly necessary, and have a tendency to become unstable when fitted to noisy or inhomogeneous data. Using Principal Component Analysis (PCA)...

Bibtex entry for this abstract:

author = {L.~Lindegren},
title={{M}inimum-dimension {L}{S}{F} modelling},
institution={Lund Observatory},
type={Technical note}