Displacement vectors that adjust for the spatial shifting of the orders with respect to a fiducial image are generated during the raw image screening process and applied to science images during the GEOM stage. These vectors include a global shift of each image and, if needed, differential order shifts. A detailed discussion of the order registration process can be found in Chapter 4.9.
Note that unlike the low-dispersion counterpart, no starting wavelength normalization correction is applied to high-dispersion data. As a result, a resampling of individual spectra to a common wavelength scale is in general required to coadd properly multiple high-dispersion images of a given source.