Split a streamed layer by a resident blade, or return its crossing points

Streams a large layer x through the engine and cuts each batch's geometry against a small resident blade layer (the QGIS "split with lines"), one batch at a time. With extract = "pieces" (the default) every feature is divided where the blade crosses it – a polygon into the faces the blade carves out, a line into the arcs between crossings – and each piece is emitted as its own row with the source attributes copied; a feature the blade does not cross passes through as a single piece. With extract = "points" the verb instead returns, per feature, the points where it meets the blade (the "line intersections" tool), dropping features that do not cross.

Usage

spatial_split(
  x,
  blade,
  extract = c("pieces", "points"),
  geom = "geometry",
  crs = NA,
  out_geom = NULL,
  flush_rows = NULL
)

Arguments

x

A vectra_node (from tbl(), tbl_tiff(), any verb chain, ...). It is consumed by the stream.

blade

An sf or sfc object whose geometry cuts the stream (typically lines, but any geometry whose boundary can node x).

extract

"pieces" (default) to emit the split pieces, or "points" to emit the intersection points of each feature with the blade.

geom

Name of the input geometry column holding hex-WKB or WKT strings. Default "geometry". Ignored when coords is given.

crs

Coordinate reference system of the input geometry, in any form sf::st_crs() accepts (EPSG integer, WKT, proj string). Defaults to the CRS the upstream node carries, or unknown.

out_geom

Name of the output geometry column. Defaults to geom (or "geometry" when coords is used).

flush_rows

Transformed rows buffered before a spill flush. Larger values mean fewer, bigger temporary files. Defaults to getOption("vectra.spatial_flush", 5e5).

Value

A vectra_node: with extract = "pieces", one row per piece carrying x's attributes; with extract = "points", one row per crossing feature carrying its intersection points. Backed by temporary .vtr spills (removed when the node is garbage-collected) and carrying the input CRS.

Details

The split is built from sf/GEOS noding and polygonization, so it expects projected or unprojected planar data; geographic coordinates are best projected first. The blade is dissolved to one geometry once and held resident while the left stream flows past. Geometry travels through the engine as hex-encoded WKB in a string column and the CRS is carried on the returned node; when blade carries no CRS it inherits the stream's. The sf package is an optional dependency (Suggests).

See also

spatial_clip() to cut against a mask without dividing into pieces, spatial_overlay() to node two polygon layers into a partition, collect_sf() to materialize as sf.

Examples

sq <- sf::st_polygon(list(rbind(c(0, 0), c(4, 0), c(4, 4), c(0, 4), c(0, 0))))
blade <- sf::st_sfc(sf::st_linestring(rbind(c(2, -1), c(2, 5))))
f <- tempfile(fileext = ".vtr")
write_vtr(data.frame(
  id = 1L, geometry = sf::st_as_binary(sf::st_sfc(sq), hex = TRUE)
), f)

# Split the square into two halves along the blade.
tbl(f) |> spatial_split(blade) |> collect_sf()
unlink(f)