OpenPTV: Open source particle tracking velocimetry. Three dimensional particle tracking velocimetry (3D-PTV) is one of the velocimetry methods, i.e a technique to measure velocity of particles. 3D-PTV is the three-dimensional method, measuring velocity and velocity gradients along particle trajectories, i.e. in Lagrangian framework, in three dimensions and in time. This is among the few techniques that can measure objects motion in the fluid flow of whatever complexity, three-dimensionality and unsteadiness. It is possible to obtain full field of velocity, velocity derivatives along with the Lagrangian acceleration and its spatial derivatives of higher moments. Read more on Wikipedia. The OpenPTV contains of: Core library written in C, called liboptv, Python/Cython bindings, shipped together with the liboptv