Skip to contents

Per-trajectory net velocity for a Tracks

Source: R/track_metrics.R
track_velocity.Rd

The net (average) velocity vector of each trajectory: its straight-line displacement divided by its elapsed duration. The magnitude is the net speed and `atan2(vy, vx)` the overall direction of travel (so a path returning to its start has zero net velocity). Distance-calibrated when a scale is set.

Usage

track_velocity(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 `data.frame` with one row per trajectory: the id column and numeric `vx`, `vy` (`NA` for tracks with fewer than two points or zero duration).

Details

Numeric (frame) time requires a frame rate ([set_frame_rate()]); POSIXct time is used directly.

See also

[velocity_vector()], [track_speed()], [track_turning()], [set_distance_scale()]

Examples

tv <- track_velocity(cpunctatus)
head(tv)
#>         trial_id            vx            vy
#> 10_1_1    10_1_1  0.0016297844  0.0018342959
#> 10_10_1  10_10_1  0.0000116351 -0.0005803454
#> 10_11_1  10_11_1  0.0004857098  0.0031564992
#> 10_12_1  10_12_1 -0.0027444592  0.0033678666
#> 10_13_1  10_13_1  0.0000000000 -0.0025758280
#> 10_14_1  10_14_1 -0.0030766624  0.0052025950
# net direction of travel of each track
head(atan2(tv$vy, tv$vx))
#> [1]  0.8443675 -1.5507504  1.4181177  2.2545541 -1.5707963  2.1048466