GENIE Gridspec Diagrams Boundary

Boundary contact regions occur where two grid tiles meet, but do not overlap. The boundary type below is suitable for grid tiles with logically-rectangular discretisations; it consists of an anchor point (a point common to both grid tiles), an "alignment" flag (used to indicate whether the anchor point is shared in index space by both tiles), and an orientation, which can be used to indicate how vector fields are transformed as they cross the boundary - for instance, whether latitudes on the first grid tile map to latitudes or longitudes on the second grid tile.