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Snap a streamed layer's coordinates to a fixed grid

Source: R/spatial.R
spatial_snap_grid.Rd

Rounds every coordinate of a streamed layer to a regular grid of spacing size (in CRS units) and repairs the result, one batch at a time. This is the fixed-precision snap-rounding the overlay noder (spatial_overlay()) applies internally, exposed as a standalone verb: it merges near-coincident vertices and removes the slivers that floating-point coordinates leave between shared boundaries, so a layer can be cleaned (or pre-noded to a common precision) without running a full overlay. Snapping is done in C straight off the hex-WKB column; one cleaned geometry comes back per input feature, so attributes ride through untouched.

Usage

spatial_snap_grid(
  x,
  size,
  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.

size

Grid spacing in CRS units (a positive number). Coordinates are rounded to the nearest multiple; a larger size snaps more aggressively.

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 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. The sf package is an optional dependency (Suggests).

See also

spatial_snap() to snap toward another layer instead of a grid, spatial_overlay() whose noding uses the same snap-rounding, collect_sf().

Examples

p <- sf::st_polygon(list(rbind(c(0.04, 0.03), c(1.02, 0.01),
                               c(0.98, 1.03), c(0.01, 0.97), c(0.04, 0.03))))
f <- tempfile(fileext = ".vtr")
write_vtr(data.frame(
  id = 1L, geometry = sf::st_as_binary(sf::st_sfc(p), hex = TRUE)
), f)

# Snap the jittered corners back onto a 0.1 grid.
tbl(f) |> spatial_snap_grid(0.1) |> collect_sf()
unlink(f)