extract_burn: Extract values from a controlledburn result at point...

In controlledburn: Sparse Geometry Rasterization with Exact Coverage Fractions

Extract values from a controlledburn result at point locations

Description

Queries the sparse tables directly; no dense matrix is created. For points at cell centres this reproduces materialize_chunk() exactly: extract_burn(x, xy, fun) == materialize_chunk(x, fun)[cbind(row, col)]

Usage

extract_burn(x, xy, fun = c("id", "sum"))

Arguments

x	A controlledburn object returned by burn().
xy	A two-column matrix or data.frame of x, y coordinates in the CRS of the burn.
fun	character, "id" (last geometry written wins, NA background) or "sum" (accumulated coverage/length/count, 0 background). Same semantics as materialize_chunk().

Details

Interior runs are matched by row equality plus column interval containment; edges, lines, and points by exact (row, col) match. Cost is O(points + hits), independent of grid dimension.

Value

A numeric vector of length nrow(xy). Points outside the grid extent are NA for both funs.

Examples

if (requireNamespace("geos", quietly = TRUE)) {
  library(geos)
  poly <- as_geos_geometry("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))")
  r <- burn(poly, extent = c(0, 10, 0, 10), dimension = c(10L, 10L))
  # value at three cell centres (fun = "id": geometry id, else NA)
  extract_burn(r, cbind(c(1.5, 5.5, 8.5), c(1.5, 5.5, 8.5)), fun = "id")
}

controlledburn documentation built on Oct. 28, 2026, 5:12 p.m.