Prepare a land mask for the grid's coastline — cc_grid_land

Turns detailed land polygons (OpenStreetMap's, for the bundled cc_grid_land) into the mask cc_grid_build() clips cells with: islets smaller than islet_min_km2 are dropped (a rock is not a hole in a cell), the coastline is pulled back shrink_m so that a position at the water's edge (a ship at its berth, a nearshore position rounded to the minute) still falls in a cell, and the result is simplified to simplify_m so the cells stay light enough to draw in a browser. A position less than shrink_m - simplify_m inland is therefore inside the grid.

Usage

cc_grid_land_prep(
  land,
  near = NULL,
  near_m = 10000,
  islet_min_km2 = 1,
  shrink_m = 300,
  simplify_m = 100,
  crs_m = 3310
)

Arguments

land: land polygons (sf or sfc, any CRS)
near: optional sf/sfc: keep only land within near_m of it (e.g. the previous grid)
near_m: distance for near, in metres (default 10 km)
islet_min_km2: drop land polygons smaller than this (default 1 km2)
shrink_m: pull the coastline back by this many metres (default 300)
simplify_m: Douglas-Peucker tolerance, in metres (default 100)
crs_m: projected CRS, in metres (default 3310)

Value

sfc of polygons in EPSG:4326