Snap a streamed layer toward a resident reference layer

Streams a large layer x through the engine and snaps each batch's vertices toward a small resident reference layer y when they lie within tolerance (in CRS units), one batch at a time (the QGIS "snap geometries to layer"). Vertices and edges of x closer than tolerance to y are pulled onto y, which closes the small gaps and overshoots between two layers that should share a boundary. The reference layer stays resident while the billion-row left stream flows past; the snap itself is sf's sf::st_snap().

Usage

spatial_snap(
  x,
  y,
  tolerance,
  geom = "geometry",
  coords = NULL,
  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.

y

An sf or sfc object: the resident reference layer to snap toward.

tolerance

Snapping distance in CRS units (a positive number). Vertices and edges of x within this distance of y are moved onto y.

geom

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

coords

Optional length-2 character vector naming the x and y coordinate columns to assemble point geometry from (e.g. c("x", "y")), for inputs such as tiff_extract_points() output. The coordinate columns are retained.

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 of the snapped geometry with x's attributes, backed by temporary .vtr spills (removed when the node is garbage-collected) and carrying the input CRS.

Details

Geometry travels through the engine as hex-encoded WKB in a string column and the CRS is carried on the returned node; use collect_sf() to materialize. When y carries no CRS it inherits the stream's. The sf package is an optional dependency (Suggests).

See also

spatial_snap_grid() to snap to a grid instead of a layer, spatial_clip() for the resident-mask streaming pattern, collect_sf().

Examples

ref <- sf::st_sfc(sf::st_linestring(rbind(c(0, 0), c(10, 0))))
line <- sf::st_linestring(rbind(c(0, 0.2), c(5, 0.1), c(10, 0.2)))
f <- tempfile(fileext = ".vtr")
write_vtr(data.frame(
  id = 1L, geometry = sf::st_as_binary(sf::st_sfc(line), hex = TRUE)
), f)

# Pull the near-zero vertices down onto the reference line.
tbl(f) |> spatial_snap(ref, tolerance = 0.5) |> collect_sf()
unlink(f)