Related to this, I'd also like to query the group for thoughts the best approach to a specific kind of analysis I have in mind with this. I'd like to know what the azimuthally averaged radiation flux is at some fixed distance r from the star plotted as a function of polar angle. My plan is to create a radiation flux derived quantity (which is why I need a derivative), then create a flux dot rhat quantity and then extract to a fixed interpolated grid and then proceed with the extracting, averaging, plotting. Does that sound like the correct approach or is there some yt functionality that I don't yet know about that might be more elegant? - ie) some way to extract the field on a spherical count our and return that as a list of values and positions.