radiusOfGyrationDT: Radius of Gyration

In topdowntimeratio: Top-Down Time Ratio Segmentation for Coordinate Trajectories

Radius of Gyration

Description

Calculates the time-weighted radius of Gyration provided a data.table containing latitude, longitude and a timestamp. This is the root-mean-square time-weighted average of all locations. Weighting by time is provided to adjust for unequal frequency of data collection.

Usage

radiusOfGyrationDT(lat_col, lon_col, timestamp, dist_measure = "geodesic")

Arguments

lat_col	Time-ordered vector of latitudes
lon_col	Time-ordered vector of longitudes
timestamp	Timestamps associated with the latitude/longitude pairs
dist_measure	Passed through to geodist::geodist_vec, One of "haversine" "vincenty", "geodesic", or "cheap" specifying desired method of geodesic distance calculation.

Details

Time-weighted RoG is defined as

sqrt(1/sum(w_j) * sum(w_j * dist(|mean_lon, mean_lat|, |lon_j, lat_j|)^2))

Where

mean_lon = sum(w_j * lon_j)/sum(w_j) and mean_lat = sum(w_j * lat_j)/sum(w_j)

And the weighting element w_j represents half the time interval during which a location was recorded

w_j = (t_j+1 - t_j-1)/2

Value

Time-weighted radius of gyration

Examples

# Inside a data.table
dt <- data.table::data.table(
  lat = c(1, 1, 1, 1, 1),
  lon = c(1, 1.5, 4, 1.5, 2),
  timestamp = c(100, 200, 300, 600, 900)
)
dt[, radiusOfGyrationDT(lat, lon, timestamp)]
# As vectors
radiusOfGyrationDT(
  c(1, 1, 1, 1, 1),
  c(1, 1.5, 4, 1.5, 2),
  c(100, 200, 300, 600, 900)
  )

topdowntimeratio documentation built on Sept. 22, 2022, 9:07 a.m.