Skip to contents

Smooth streamed line and polygon geometry

Source: R/spatial.R
spatial_smooth.Rd

Rounds the corners of every line and polygon in a streamed layer by Chaikin corner-cutting, one batch at a time. Each iteration replaces every vertex with two points a quarter and three-quarters of the way along its adjacent edges, so sharp angles become a sequence of short chamfers that read as a smooth curve; more iterations give a smoother result with more vertices. Open lines keep their endpoints (keep_ends); polygon rings are cut cyclically and shrink slightly, as Chaikin smoothing does. Point geometry passes through unchanged.

Usage

spatial_smooth(
  x,
  iterations = 2L,
  keep_ends = TRUE,
  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.

iterations

Number of corner-cutting passes (a positive integer). Each pass roughly doubles the vertex count. Default 2.

keep_ends

If TRUE (default), pin the first and last vertex of an open line so it is not shortened at its tips. Ignored for closed rings.

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

Details

The smoothing is computed directly on the coordinates (no GEOS call), so it is dependency-light; sf is used only to decode and rebuild each batch. 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.

See also

spatial_map() for per-feature transforms such as densifying with ~ sf::st_segmentize(.x, dfMaxLength) or sampling points along a line with ~ sf::st_line_sample(.x, n), collect_sf() to materialize as sf.

Examples

zig <- sf::st_linestring(rbind(c(0, 0), c(1, 1), c(2, 0), c(3, 1), c(4, 0)))
f <- tempfile(fileext = ".vtr")
write_vtr(data.frame(
  id = 1L, geometry = sf::st_as_binary(sf::st_sfc(zig), hex = TRUE)
), f)

# Smooth the zig-zag with three corner-cutting passes.
tbl(f) |> spatial_smooth(iterations = 3) |> collect_sf()
unlink(f)