Skip to contents

Per-observation instantaneous speed for a Tracks

Source: R/track_metrics.R
instantaneous_speed.Rd

Instantaneous speed at each point, aligned to the `Tracks`'s rows (the per-observation sibling of [elapsed_seconds()]). Each point carries the speed of the step that ends at it; the first point of every trajectory is `NA`. Speeds come from [step_speed()] using the track's elapsed time from [elapsed_seconds()].

Usage

instantaneous_speed(ts, x_col = ts@cols$x, y_col = ts@cols$y)

Arguments

ts

A `Tracks`.

x_col, y_col

Names of the coordinate columns. Default to the `Tracks`'s recorded x/y columns.

Value

A numeric vector, one value per observation in `ts@data` order, `NA` at each trajectory's first point.

Details

Numeric (frame) time requires a frame rate ([set_frame_rate()]); POSIXct time is used directly. With the default coordinate columns the unit is radii per second.

See also

[step_speed()], [track_speed()], [elapsed_seconds()]

Examples

summary(instantaneous_speed(cpunctatus))
#>     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.      NAs 
#> 0.000000 0.000000 0.001030 0.001609 0.002505 0.333357      235