ddbs_line_interpolate: Interpolates a point or points along a line geometry

In duckspatial: R Interface to 'DuckDB' Database with Spatial Extension

Interpolates a point or points along a line geometry

Description

Returns either a single point at a specified position along a line, or multiple equally-spaced points along a line, depending on the value of intervals. When intervals = FALSE, this wraps ST_LineInterpolatePoint; when intervals = TRUE, it wraps ST_LineInterpolatePoints.

Usage

ddbs_line_interpolate(
  x,
  fraction = 0.5,
  intervals = 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.
fraction	a numeric value between 0 and 1. When intervals = FALSE, specifies the position along the line to interpolate, where 0 is the start and 1 is the end. When intervals = TRUE, specifies the spacing between interpolated points as a proportion of the total line length. Defaults to 0.5.
intervals	a logical value. If FALSE (default), returns a single POINT at the position given by fraction. If TRUE, returns a MULTIPOINT of equally-spaced points along the line at intervals defined by fraction.
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

## Not run: 
## load package
library(duckspatial)

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

## return the midpoint of a line (default)
ddbs_line_interpolate(rivers_ddbs)

## return the point 25% along the line
ddbs_line_interpolate(rivers_ddbs, fraction = 0.25)

## return equally-spaced points every 10% of the line length
ddbs_line_interpolate(rivers_ddbs, fraction = 0.1, intervals = TRUE)

## return equally-spaced points every 50% of the line length (i.e. midpoint and end)
ddbs_line_interpolate(rivers_ddbs, fraction = 0.5, intervals = TRUE)

## End(Not run)

duckspatial documentation built on June 22, 2026, 9:08 a.m.