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Aggregate the intersection of geometries

Source: R/ddbs_union.R
ddbs_intersection_agg.Rd

Computes the geometric intersection of a set of geometries — the area common to all of them — using DuckDB's ST_Intersection_Agg() aggregate. This is the intersection counterpart to ddbs_union_agg().

Usage

ddbs_intersection_agg(
  x,
  by = NULL,
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

Arguments

x

Input spatial data. Can be:

  • A duckspatial_df object (lazy spatial data frame via dbplyr)

  • An sf object

  • A tbl_lazy from dbplyr

  • A character string naming a table/view in conn

Data is returned from this object.

by

Character vector of one or more column names to group by. The intersection is computed within each group. When NULL (default), all geometries are intersected into a single geometry.

conn

A connection object to a DuckDB database. If NULL, the function runs on a temporary DuckDB database.

name

A character string of length one specifying the name of the table, or a character string of length two specifying the schema and table names. If NULL (the default), the function returns the result as an sf object

mode

Character. Controls the return type. Options:

  • "duckspatial" (default): Lazy spatial data frame backed by dbplyr/DuckDB

  • "sf": Eagerly collected sf object (uses memory)

Can be set globally via ddbs_options(mode = "...") or per-function via this argument. Per-function overrides global setting.

overwrite

Boolean. whether to overwrite the existing table if it exists. Defaults to FALSE. This argument is ignored when name is NULL.

quiet

A logical value. If TRUE, suppresses any informational messages. Defaults to FALSE.

Value

Depends on the mode argument (or global preference set by ddbs_options):

  • duckspatial (default): A duckspatial_df (lazy spatial data frame) backed by dbplyr/DuckDB.

  • sf: An eagerly collected object in R memory, that will return the same data type as the sf equivalent (e.g. sf or units vector).

When name is provided, the result is also written as a table or view in DuckDB and the function returns TRUE (invisibly).

Examples

if (FALSE) { # \dontrun{
## load package
library(duckspatial)

## create a connection and three overlapping polygons
conn <- ddbs_create_conn()
polys <- sf::st_as_sf(
  data.frame(grp = c("a", "a", "a")),
  geometry = sf::st_sfc(
    sf::st_polygon(list(matrix(c(0,0, 3,0, 3,3, 0,3, 0,0), ncol = 2, byrow = TRUE))),
    sf::st_polygon(list(matrix(c(1,1, 4,1, 4,4, 1,4, 1,1), ncol = 2, byrow = TRUE))),
    sf::st_polygon(list(matrix(c(2,2, 5,2, 5,5, 2,5, 2,2), ncol = 2, byrow = TRUE))),
    sf::st_polygon(list(matrix(c(3,3, 6,3, 6,6, 3,6, 3,3), ncol = 2, byrow = TRUE)))
  ),
  crs = 4326
)

## intersect all geometries into their common area
polys_inters <- ddbs_intersection_agg(polys, mode = "sf")

## intersect within groups
polys_inters_grp <- ddbs_intersection_agg(polys, by = "grp", mode = "sf")

## plot them
plot(polys["grp"], key.pos = NULL, reset = FALSE)
plot(polys_inters_grp["grp"], pal = c("red", "blue"), add = TRUE)
plot(sf::st_geometry(polys_inters), col = "black", pch = 19, cex = 2, add = TRUE)
} # }