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Compute the concave hull of geometries

Source: R/ddbs_ops_unary.R
ddbs_concave_hull.Rd

Returns the concave hull that tightly encloses the geometry, capturing its overall shape more closely than a convex hull.

Usage

ddbs_concave_hull(
  x,
  ratio = 0.5,
  allow_holes = TRUE,
  conn = NULL,
  name = NULL,
  crs = NULL,
  crs_column = "crs_duckspatial",
  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.

ratio

Numeric. The ratio parameter dictates the level of concavity; 1 returns the convex hull, while 0 indicates to return the most concave hull possible. Defaults to 0.5.

allow_holes

Boolean. If TRUE (the default), it allows the output to contain holes.

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

crs

Deprecated The coordinates reference system of the data. Specify if the data doesn't have a crs_column, and you know the CRS.

crs_column

Deprecated a character string of length one specifying the column storing the CRS (created automatically by ddbs_write_vector). Set to NULL if absent.

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)
library(sf)

# create points data
n <- 5
points_ddbs <- data.frame(
  id = 1,
  x = runif(n, min = -180, max = 180),
  y = runif(n, min = -90, max = 90)
) |>
  ddbs_as_spatial(coords = c("x", "y"), crs = 4326) |>
  ddbs_combine()

# option 1: passing ddbs or sf objects
output1 <- duckspatial::ddbs_concave_hull(points_ddbs, mode = "sf")

plot(output1)


# option 2: passing the name of a table in a duckdb db

# creates a duckdb
conn <- duckspatial::ddbs_create_conn()

# write sf to duckdb
ddbs_write_vector(conn, points_ddbs, "points_tbl")

# spatial join
output2 <- duckspatial::ddbs_concave_hull(
 conn = conn,
 x = "points_tbl",
 mode = "sf"
)

plot(output2)

} # }