Read the Natural Earth glaciated-areas ice layer

Reads ne_10m_glaciated_areas, the ice source for build_polycell_support(). A few features are invalid under the spherical s2 engine and GEOS-level sf::st_make_valid() does not repair them, so sf::st_area() aborts with "Loop 0 is not valid". Those features are repaired under the planar engine, and any that remain invalid are measured with terra::expanse(), which does not go through s2, and reported rather than silently dropped.

The layer is a coarse present-day snapshot, so ice area does not vary historically. That is acceptable only while ice is a reporting category rather than a driver.

Usage

read_glaciated_areas(dir = NULL)

Arguments

dir

Directory holding the shapefile. Defaults to Sys.getenv("WHEP_NATURALEARTH_DIR"), under which the layer is expected at ne_10m_glaciated_areas/ne_10m_glaciated_areas.shp.

Value

An sf table of glaciated polygons in WGS84, carrying a s2_repaired logical column. The "unrepaired" attribute is a tibble of the features that stayed s2-invalid, with their terra::expanse() area.

Examples

# Requires WHEP_NATURALEARTH_DIR to be set; not run without it.
if (nzchar(Sys.getenv("WHEP_NATURALEARTH_DIR"))) {
  read_glaciated_areas()
}