The velocity components (`vx`, `vy`) at each point, aligned to the `Tracks`'s
rows. Each point carries the velocity of the step that ends at it (step
displacement divided by its elapsed time); the first point of every trajectory
is `NA`. The magnitude is [instantaneous_speed()] and the direction is
`atan2(vy, vx)`.
Usage
velocity_vector(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 columns `vx` and `vy`, one row 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 a distance calibration ([set_distance_scale()]) the
components are in physical units per second; otherwise coordinate units per
second.
See also
[instantaneous_speed()], [angular_velocity()], [set_distance_scale()]
