Thin points dataset based on geographic and temporal distance

This function thins a dataset so that only observations that have a distance from each other greater than "dist_min" in space and "interval_min" in time are retained.

Usage

thin_by_dist_time(
  data,
  dist_min,
  interval_min,
  coords = NULL,
  time_col = "time",
  lubridate_fun = c,
  dist_method = c("great_circle", "euclidean")
)

Arguments

data

An sf::sf data frame, or a data frame with coordinate variables. These can be defined in coords, unless they have standard names (see details below).

dist_min

Minimum distance between points (in units appropriate for the projection, or meters for lonlat data).

interval_min

Minimum time interval between points, in days.

coords

A vector of length two giving the names of the "x" and "y" coordinates, as found in data. If left to NULL, the function will try to guess the columns based on standard names c("x", "y"), c("X","Y"), c("longitude", "latitude"), or c("lon", "lat")

time_col

The name of the column with time; if time is not a lubridate object, use lubridate_fun to provide a function that can be used to convert appropriately

lubridate_fun

function to convert the time column into a lubridate object

dist_method

method to compute distance, either "euclidean" or "great_circle". Defaults to "great_circle", which is more accurate but takes slightly longer.

Value

An object of class sf::sf or data.frame, the same as "data".

Details

Geographic distances are measured in the appropriate units for the projection used. In case of raw latitude and longitude (e.g. as provided in a data.frame), the crs is set to WGS84, and units are set to meters. Time interval are estimated in days. Note that for very long time period, the simple conversion x years = 365 * x days might lead to slightly shorter intervals than expected, as it ignores leap years. The function y2d() provides a closer approximation.

This function an algorithm analogous to spThin, with the exception that neighbours are defined in terms of both space and time.