GENIE Gridspec Diagrams UnstructuredCell

Unstructured cells provide detailed structural information about cells. Unstructured cells are particularly useful for high-resolution grids that must cover detailed topography -- for instance numerically generated "unstructured triangular" discretisations. Vertices are specified using an appropriate point type, the only available one of which is currently a geo-referenced type consisting of geographic longitude and latitude coordinates.

Since vertices are likely to be shared between cells, it may be more appropriate to associate vertices with a tile instead of a cell, and reference the vertices from cells instead (a similar thing is done for edges). This will avoid storing duplicate vertex data.