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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), 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)

## 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)
} # }