The ParticleTracer/ParticlePath/StreakLine filters which are subclasses of vtkParticleTracerBase have the following improvements:
 Multithreaded using vtkSMPTools. Multithreading is used when there is only one MPI process, and the number of particles is greater than 100.
 Now have InterpolatorType which can either use a cell locator (default) or a point locator for interpolation.
 Instead of the StaticMesh flag, it now has the MeshOverTime flag which has the following values:
 Different: The mesh is different over time.
 Static: The mesh is the same over time.

Linear Transformation: The mesh is different over time, but it is a linear transformation of the first
timestep's mesh.
 For cell locators, this flag internally makes use of the new vtkLinearTransformCellLocator. This way the locator is only built once in the first timestep.
 For point locators, this flag internally reuses the same cell links, but rebuilds the point locator since there is no vtkLinearTransformPointLocator yet.

Same Topology: The mesh is different over time, but it preserves the same topology (same number of
points/cells, same connectivity).
 For cell locators, this is equivalent to MeshOverTime == Different.
 For point locators, this flag internally reuses the same cell links.