I don’t see preprocessed_xyt.csv in the repo. Not sure where it’s coming from, but I guess you ran their R code and exported it as a csv? If you upload it somewhere I’ll use your exact code as a starting point and see if I can be more helpful (I’m having trouble installing the required R packages to run their data script). I already see a typo in your gk function (should have 0.5 / np.pi).