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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,
  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), no table is written and the result is returned as a duckspatial_df or sf object, depending on mode

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")) |>
  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)

} # }