The wavelength solution calibration files can be created using arc frames and the Recipe Editor (from the GPI pipeline) with the Recipe Category : Calibration and the Recipe Template : Wavelength Solution 2D.
This is a more computationally intensive reduction and it may take some time to complete. It also requires a reference wavelength solution in the same band as the observed arc lamp data (zip file attached to this post). This zip file can also be accessed by downloading the Wavecals_reference.zip file available on the `Gemini Public Data webpage : http://www.gemini.edu/sciops/instruments/gpi/public-data. These files should be added to the calibrations directory.