Multiple staggers in GRIDSPEC

[Oehmke]

Currently the ​CF GRIDSPEC convention only represents the grid information for a single stagger location. In this ticket we propose an addition to the convention to allow it to express multiple staggers at once. This change will allow users who have data fields on different staggers (e.g. wind velocity components) to only have one mosaic to describe the grid for both data fields. This has the benefit of reducing the amount of redundant information and also producing a clearer representation of the structure of the data. There are two proposed methods to allow the multiple staggers.

The first method is to increase the resolution of a GRIDSPEC tile to allow it hold the information for all staggers at once. This "supergrid" method was proposed in the original GRIDSPEC document. For an in-depth description of our implementation of this method see here: ​http://earthsystemcog.org/projects/esmf/gridspec_stagger_supergrid.

The second method is allow a GRIDSPEC tile file to contain multiple versions of each tile each with a possibly different size. Each of these tile versions would contain the information for a separate stagger. For an in-depth description of this method see here: ​http://earthsystemcog.org/projects/esmf/cf_stagger

In addition to the usual refinement of a proposal by community comment, part of the aim of this ticket is to narrow these two proposals down to one, any comments in this regard are also welcome.