Hello Scott,
For my elliptic solver, I need to know not only if a given grid boundary is an outer boundary or not, I need to know if it's an inter-processor boundary or a mesh refinement boundary. cctk_bbox does not provide the latter distinction. Is there something analogous provided by Carpet?
GenericFD's GenericFD_GetBoundaryInfo routine (in Kranc, see https://github.com/ianhinder/Kranc/blob/6bed8e74aac5bd1e76f2e7a4d8efcf166a60...) will do this for you. I believe there was discussion at one point to move this functionality into the flesh but cannot find the thread right now.
Yours, Roland