Once the geometrical transformation has been defined and all processing dependent on the original geometrical pattern of the image has been completed, it is a simple matter to apply the geometrical transformation to straighten the spectral orders and align slit images with image lines.
The current geometrical transformations are applied to images in a dataset using the redxspec task by setting the transform flag. The current transformations are the transformations defined by the fit files located in the directory pointed to by the IRAF environment variable database$. Each order of the object, sky, and comparison images, if present, are transformed separately and subsetted into separate files, with separate wavelength calibrations stored in their headers. The separate file names are formed by appending .o##, .a##, .b##, .s##, or .c## (depending on whether the observation type header entry is abba, soos, osso, or comparison) to the base spectrum name, where ## is the number of the spectral order.