Functions for detecting eye fixations in raw eye-tracking data. The detection is done using a velocity-based algorithm for saccade detection proposed by Ralf Engbert and Reinhold Kliegl in 2003. The algorithm labels segments as saccades when the velocity of the eye movement exceeds a certain threshold. Anything between two saccades is considered a fixation. Thus the algorithm is not appropriate for data containing episodes of smooth pursuit eye movements.