Grids and cell indices

DiscreteGlobalGrids separates a grid's geometry from the values stored on it. These concepts also apply to regional grids and grids without a hierarchy.

Grids and systems

A grid is a finite collection of cells. An H3 grid at level 12 is a grid; so is a selected region of that level. Geometry, point queries and neighbourhood operations act on grids.

A system defines related grids at several levels, including their parent and child relationships. levelgrid(sys, level) selects one complete level. A grid can also supply its geometry directly, as an ocean-model grid might.

The grid interface documents both abstractions. Writing a grid system implements a complete example, and the architecture guide describes the generic algorithms.

Cell ids and array positions

A cell id identifies a cell independently of the array that stores its value. A local index identifies a position in one collection. Selecting a region changes local positions while preserving cell ids.

A Cells dimension connects those identities to array values. Use it to select data by point or region, while ordinary integer indexing selects positions in the current array.

Choose a container

A PartialGrid provides grid operations on a subset. A CellVector provides ordered cell identities. A CellLookup attaches those identities to a Cells dimension. A MultiOrderCellSet can store cells at different levels. Use the conversion table to move between these forms without changing the association between cells and values.