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Locate geometries at specific M values

Source: R/ddbs_dimensions_ops.R
ddbs_locate.Rd

Return the geometries at a specific M values or range of M values.

Usage

ddbs_locate_along(
  x,
  measure,
  offset = 0,
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

ddbs_locate_between(
  x,
  start_measure,
  end_measure,
  offset = 0,
  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.

measure

A numeric value specifying the M value at which to locate a point along the geometry. Used only by ddbs_locate_along.

offset

A numeric value specifying a lateral offset to apply perpendicular to the line direction at the located point(s). Default is 0 (no offset).

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.

start_measure

A numeric value specifying the lower bound of the M range.

end_measure

A numeric value specifying the upper bound of the M range.

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

  • ddbs_locate_along(): returns a point or multi-point, containing the point(s) at the geometry with the given measure

  • ddbs_locate_between(): returns a geometry or geometry collection created by filtering and interpolating vertices within a range of "M" values

Examples

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

## read data (must contain M-enabled linestring geometries)
rivers_ddbs <- ddbs_open_dataset(
  system.file("spatial/rivers.geojson",
  package = "duckspatial")
)

## Calculate the length of the rivers
rivers_agg_ddbs <- rivers_ddbs |> 
  ddbs_union_agg("RIVER_NAME") |> 
  ddbs_length()

## Add M dimension to the rivers
rivers_m_ddbs <- rivers_agg_ddbs |> 
  ddbs_force_3d("length", dim = "M")

## Locate rivers with M between 10000 and 20000
ddbs_locate_between(rivers_m_ddbs, 10000, 20000)

} # }