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Get the envelope (bounding box) of geometries

Source: R/ddbs_extent_funs.R
ddbs_envelope.Rd

Returns the minimum axis-aligned rectangle that fully contains the geometry.

Usage

ddbs_envelope(
  x,
  by_feature = FALSE,
  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_feature

Logical. If TRUE, the geometric operation is applied separately to each geometry. If FALSE, the geometric operation is applied to the data as a whole.

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).

Details

ST_Envelope returns the minimum bounding rectangle (MBR) of a geometry as a polygon. For points and lines, this creates a rectangular polygon that encompasses the geometry. For polygons, it returns the smallest rectangle that contains the entire polygon.

When by_feature = FALSE, all geometries are combined and a single envelope is returned that encompasses the entire dataset.

Examples

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

# read data
argentina_ddbs <- ddbs_open_dataset(
  system.file("spatial/argentina.geojson", 
  package = "duckspatial")
)

# input as sf, and output as sf
env <- ddbs_envelope(x = argentina_ddbs, by_feature = TRUE)

# create a duckdb database in memory (with spatial extension)
conn <- ddbs_create_conn(dbdir = "memory")

# store in duckdb
ddbs_write_table(conn, argentina_ddbs, "argentina")

# envelope for each feature
env <- ddbs_envelope("argentina", conn, by_feature = TRUE)

# single envelope for entire dataset
env_all <- ddbs_envelope("argentina", conn, by_feature = FALSE)

# create a new table with envelopes
ddbs_envelope("argentina", conn, name = "argentina_bbox", by_feature = TRUE)
} # }