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Locate a point along a linestring

Source: R/ddbs_ops_unary_line.R
ddbs_line_locate_point.Rd

Returns a value between 0 and 1 representing the position of the closest point on the line to the reference point, as a fraction of the line's total length. 0 corresponds to the start of the line and 1 to the end.

Usage

ddbs_line_locate_point(
  x,
  y,
  new_column = "line_fraction",
  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.

y

The reference point. One of:

  • An sf object with exactly 1 point feature.

  • A duckspatial_df with exactly 1 point feature.

  • A character string naming a DuckDB table that contains exactly 1 point feature (requires conn).

new_column

Name of the new column to create on the input data. Ignored with mode = "sf".

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)

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

## define a single reference point (sf with 1 row)
ref_pt <- sf::st_sf(
  geometry = sf::st_sfc(sf::st_point(c(-8, 43)), crs = 4326)
)

## locate the fraction along each river closest to the reference point
ddbs_line_locate_point(rivers_ddbs, y = ref_pt)
} # }