The shape of the dispersed image in the cross-dispersion direction is parameterized as a function of dispersion angle . The parameterization is a superposition of Gaussian and a Lorentzians.

This parameterization is independent of the source position in the FOV
along the dispersion direction. In the cross-dispersion direction,
the location of the dispersed image is shifted according to

where is the component of the off-axis angle in the cross-dispersion direction, and is the distance between RGA and RFC.

The parameterizations are evaluated at each bin in by integration over the entire width of the bin.

The functions have the following forms. The Gaussian function
is parameterized by

and the Lorentzian is parameterized by

Michael Smith 2011-09-20