Get speed
get_speed.RdGets an individual's speed over time, using a specified time step to compute the speed
Arguments
- x_i
x coordinates of the individual (a vector whose length is the number of timesteps) or of a group centroid
- y_i
y coordinates of the individual (a vector whose length is the number of timesteps) or of the group centroid
- time_res
the number of seconds between timestamps (e.g. for data recorded at 1 Hz, the value would be 1, for data recorded every 30 sec, the value would be 30)
- t_window
the time window over which to compute speed (number of time steps into the future or past)
- forward
a boolean value (defaults to T) indicating whether to compute speeds forward in time (if T) or backward in time (if F)
Value
Returns speeds: a time series of the speed of individual (a vector of the same length as x_i and y_i)
Details
The speed is computed as speeds[t] = sqrt ( (x_i[t+t_window] - x_i[t] )^2 + ( y_i[t+t_window] - y_i[t] )^2 ) / (time_res * t_window)
Note that by default speeds[t] gives the instantaneous speed between time t and time t + t_window, i.e. the speeds are computed
based on the future not on the past. If forward is set to F, the speeds will be computed based on the past, as:
speeds[t] = sqrt ( (x_i[t] - x_i[t-t_window] )^2 + ( y_i[t] - y_i[t-t_window] )^2 ) / (time_res * t_window)