I have a problem where I am looking at a circular structure and I want to examine the spatial correlation pattern in the random effects portion of the model. I am looking at 8 sectors of a circular patch, and plan to use the corExp class. The sector number is the position variable, but for the calculation of the distance between two sectors I need to take into account the fact that the sectors are arranged in a circular pattern. I have read through some of the NLME documentation, it is not clear to me how I can specify the "distance function" appropriately. Any help/suggestions would be much appreciated. Michael Jerosch-Herold