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Cells intersecting a polygon

Source: R/calc.R
cells_in_polygon.Rd

Returns cell_id + pct_covered (0-100) for the cells a polygon overlaps. pct_covered is the fraction of each cell inside the polygon, and it is not cosmetic — scores_for_cells() and species_for_cells() weight by it, so partially covered edge cells count proportionally.

Usage

cells_in_polygon(poly, src, res = 0.05)

Arguments

poly

an sf polygon (assumed or transformable to EPSG:4326)

src

a DBI connection (preferred), or a single-layer terra::SpatRaster of integer cell ids

res

grid resolution in degrees, SQL path only (default 0.05)

Value

a tibble with columns cell_id (integer) and pct_covered (0-100)

Details

Pass a DB connection. Then the grid is read from the database being queried and cannot disagree with it. Two paths, chosen automatically:

  • v8 (cell carries lon/lat) — a SQL bbox select on cell picks the candidates and sf computes exact coverage on just those. No raster is touched. For a 2x1.5-degree area this is ~0.02 s against ~35 s to read the whole cell-id raster, and it joins cell_model, which is already cell-oriented.

  • v7 (no lon/lat) — falls back to cell_id_raster(), the 0-360 regional raster that IS v7's grid.

Passing a terra::SpatRaster directly still works, but nothing can then verify it matches the database — see cell_id_raster() for how that failed silently on v8.