Observation data must be converted to MIDAS data structures before processing and the spectra must be oriented so that the dispersion direction is along the rows of the images, with the wavelength increasing from left to right. The command INTAPE/FITS can be used to read FITS files from a magnetic tape or from disk. The commands ROTATE/CLOCK, ROTATE/COUNTER_CLOCK and FLIP/IMAGE enable to perform any rotation by a multiple of 90 degrees and image flipping without interpolating the pixel values. The command REBIN/ROTATE can be used for any rotation but in the general case will interpolate the pixel values.