Skip to contents

Coerce an sf object to clusterTrack data format

Source: R/ctdf.R
as_ctdf.sf.Rd

Converts an sf object with POINT geometries and a timestamp column to a ctdf. The source CRS is taken from x; a missing CRS is an error.

Usage

# S3 method for class 'sf'
as_ctdf(x, time = "time", t_srs = "+proj=eqearth", ...)

Arguments

x

An sf object with POINT geometries and a source CRS.

time

Name of the POSIXt time column. Will be renamed to "timestamp" internally.

t_srs

Target spatial reference passed to sf::st_transform(). Default is "+proj=eqearth".

...

Currently unused

Value

An object of class ctdf (inherits from data.table and data.frame), with an sfc_POINT geometry column named location.

Details

Rows are sorted by timestamp, geometry is transformed to t_srs, and clusterTrack columns are initialized. Existing reserved columns are overwritten with a warning.

The converted object is checked for duplicate locations with the same timestamp and temporal gaps exceeding getOption("clusterTrack.max_gap", 24) hours. Duplicate warnings identify row positions in the returned, timestamp-sorted ctdf.

ctdf columns

In addition to columns retained from the input, a ctdf contains the following standardized columns:

  • timestamp: Observation time. Rows are ordered by this column when the ctdf is created.

  • location: Point geometry in the target coordinate reference system.

  • .id: Sequential row identifier assigned after ordering by timestamp. It is used internally to track locations through the clustering workflow and does not refer to the row number in the original input.

  • cluster: Final cluster assignment. It is initialized to NA. cluster_track() assigns positive integers to clustered locations and 0 to unassigned locations. aggregate_ctdf() may subsequently merge and renumber clusters.

  • lof: Local Outlier Factor score for each location. It is initialized to NA and populated by ctdf_lof() for locations with cluster > 0. Unassigned locations retain NA.

See also

as_ctdf(), as_ctdf.data.frame()

Examples

data(mini_ruff)
points <- sf::st_as_sf(
  mini_ruff,
  coords = c("longitude", "latitude"),
  crs = 4326
)
x <- as_ctdf(points)