Geometry Decomposition.

gibble

The goal of gibble is to provide a straightforward map of path-based data structures. Paths are connected linear sequences of coordinates, otherwise known as lines. Structured spatial data includes objects composed of paths, which are islands, holes within island, lines, and points. Polygons require an extra grouping level subobject to ensure holes are nested within their island, but this is ignored for other types.

The map is simply a record of the path, its size (number of vertices and geometric dimension), its groupings (which object and subobject), and its type (something like “polygon”, “line”, “point”). Internally a bare functionality works with matrices and all numeric values, but gibble then turns this set of values into a data frame where entities can be labelled arbitrarily.

Sequential linear structures are not optimal for many operations when working with spatial data, and in particular they cannot describe surfaces in 3D geometry because they are inherently, topologically, one-dimensional. Gibble provides a simple bridge between path and primitive types, which do generalize to any topological dimension. Gibble considers a point to be a degenerate path, so that the path concept is consistent for any simple features-analogue.

The original impetus for gibble was to illustrate how basic topological editing might be provided via the mapedit package, and is used to consolidate the geometry decomposition tools in silicate.

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