This visual element renders a set of continuous lines to visualize the trajectories of motion of particles. Normally, the element is automatically created by the program when you apply the Generate trajectory lines modifier.
The option Wrap trajectory lines folds trajectory lines leaving the periodic simulation cell back into the cell. Note that this option will yield correct results only if the simulation cell size is not changing with time.
The option Show up to current time only restricts rendering of trajectories lines to those parts that have been traversed by particles at the current animation time. Thus, the trajectory lines will get gradually drawn while playing the animation, just as in the examples seen here and on this page.
ovito.vis.TrajectoryVis (Python API)