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Extract the start or end point of a linestring geometry

Source: R/ddbs_ops_unary.R
ddbs_endpoint_startpoint.Rd

Returns the first or last point of a LINESTRING geometry. These functions only work with LINESTRING geometries (not MULTILINESTRING or other geometry types).

Usage

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

ddbs_endpoint(
  x,
  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.

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).

Details

These functions wrap DuckDB Spatial's ST_StartPoint and ST_EndPoint. Input geometries must be of type LINESTRING (MULTILINESTRING is not supported). For each input feature, the first or last coordinate of the LINESTRING is returned as a POINT geometry.

Examples

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

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

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

## store in duckdb
ddbs_write_vector(conn, rivers_ddbs, "rivers")

## extract start points
ddbs_startpoint(conn = conn, "rivers")

## extract end points
ddbs_endpoint(conn = conn, "rivers")

## without using a connection
ddbs_startpoint(rivers_ddbs)
ddbs_endpoint(rivers_ddbs)
} # }