This application takes a FLAIR frame stored in an NDF with the
dispersion along the y axis, and extracts the individual spectra
using an optimal extraction. It stores the spectra in an output
two-dimensional NDF, configured such that the dispersion is along
x axis, and wavelength increases with pixel index, and each
spectrum occupies one line.
This assumes stability (x positions of the fibres do not move),
and vertical orientation of the fibres. These are satisfied by
FLAIR (Parker, private communication).