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Create and cache grid polygons over a boundary

Source: R/stable-ids-cache.R
create_grid_polygons_cached.Rd

Builds a grid via create_grid_polygons() and memoizes the result so repeated calls with the same inputs return instantly.

Usage

create_grid_polygons_cached(
  boundary,
  target_cells = NULL,
  type = c("square", "hex"),
  ...,
  cache_env = .gmt_cache,
  max_entries = 50L
)

Arguments

boundary

An sf or sfc polygonal object.

target_cells

Approximate desired number of cells. Default NULL, as in create_grid_polygons(), so the grid can be sized by cellsize or n passed through ... instead.

type

Grid type: "square" (the default) or "hex", matching create_grid_polygons().

...

Additional arguments forwarded to create_grid_polygons().

cache_env

Environment for memoized grids. Default .gmt_cache.

max_entries

Maximum number of grids the cache holds. Default 50. Once full, adding a grid evicts the one added earliest, so a loop over many boundaries holds at most this many grids (about 2 MB per 2,500-cell grid) rather than every grid it ever built for the life of the session. clear_grid_cache empties it outright.

Value

An sf data frame with a stable poly_id column. The rows are re-ordered and re-numbered by ensure_stable_poly_id, which create_grid_polygons does not do: the same cell therefore carries a different poly_id depending on which of the two builders produced it. Use one builder throughout an analysis; joining a summary keyed on IDs from one onto geometries from the other draws the values on the wrong polygons.

See also

Other tessellation: build_tessellation(), create_grid_polygons(), create_voronoi_polygons(), ensure_stable_poly_id(), get_voronoi_seeds(), plot_tessellation_map(), voronoi_seeds_kmeans(), voronoi_seeds_random()

Other package options and caches: clear_fitted_cache(), clear_grid_cache(), spatialkit_quiet()

Examples

library(sf)
bnd <- st_sf(geometry = st_sfc(st_polygon(list(rbind(
  c(0, 0), c(100, 0), c(100, 100), c(0, 100), c(0, 0)
))), crs = 32632))
g <- create_grid_polygons_cached(bnd, target_cells = 16, type = "hex")
nrow(g)
#> [1] 27
# The IDs come from ensure_stable_poly_id(), so they follow the geometry:
# the same request with the boundary's vertices in another order gives the
# same ID to the same cell.
bnd2 <- st_sf(geometry = st_sfc(st_polygon(list(rbind(
  c(100, 100), c(0, 100), c(0, 0), c(100, 0), c(100, 100)
))), crs = 32632))
g2 <- create_grid_polygons_cached(bnd2, target_cells = 16, type = "hex")
same_cell <- match(st_as_text(st_geometry(g2)), st_as_text(st_geometry(g)))
all(g2$poly_id == g$poly_id[same_cell])
#> [1] TRUE