11.1.2 Geometry

With the exception of block-centered grids, which have no explicit geometry, the geometry of a grid is based upon the geometry of points. Points may be specified explicitly, e.g., by three (X,Y,Z) coordinates, or implicitly using parametric spline representations. The geometry of any grid is based upon a lowest order description but with additive optional extensions. The latter is a deliberate design to facilitate grid transfers.