sample_fixations

Sample fixation coordinates at arbitrary time points.

Usage

sample_fixations(x, time, ...)

# S3 method for class 'fixation_group'
sample_fixations(x, time, fast = TRUE, ...)

Arguments

x

the fixation group

time

the continuous time points to sample

...

Additional arguments passed to methods.

fast

Logical. If TRUE (default), uses a vectorized lookup; if FALSE, evaluates each time point in turn. Both paths first order the fixations by onset (keeping the input order among tied onsets) and drop fixations with a missing onset, so they return the same coordinates for any input order; of tied onsets, the last one is used.

Value

A data frame of class sampled_fixation_group with one row per time point and columns x, y (NA before the first onset), onset (the time point) and duration (1).

Details

Each time point takes the coordinates of the most recent fixation whose onset is at or before it. Fixation durations are not used: gaze during a saccade is attributed to the preceding fixation, and the last fixation is held for all later time points. Time points before the first onset give NA.

Examples

fg <- fixation_group(x = c(100, 200, 300), y = c(100, 150, 200),
                     onset = c(0, 200, 400), duration = c(200, 200, 200))
sample_fixations(fg, time = c(-50, 0, 250, 500))
#> Fixation group: 4 fixations
#>   x range: [100, 300]
#>   y range: [100, 200]
#>   duration range: [1, 1]
#>   onset range: [-50, 500]