3D Particle Tracking Velocimetry software on Github ( http://3dptv.github.com )

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An introduction to 3D-PTV (a bit old ...)


On-line presentation about 3D-PTV


Our main goal is to promote the 3D-PTV experimental technology and open it for the worldwide use. We are convinced that this technique can make an impact in various applications, allowing for the researchers and industry to get a deeper insight into their flows. Most of the flows are highly complex and turbulent and only few of them can get a limited low-dimensional or analytical description that explains the different flow phenomena. Experimental research is inevitable in observing the flow and discovering new phenomena, in addition to assisting to explain the old ones.


The 3D Particle Tracking Velocimetry (PTV) offers a flexible technique for the determination of velocity fields in flows. It is based on the visualization of a flow with small, neutrally buoyant particles and a stereoscopic recording image sequences of the particles. In the past decade the successful research work performed by the Institute of Geodesy and Photogrammetry at ETH Zurich led to an operational and reliable measurement tool used in hydrodynamics and space applications. In cooperation with the Institute of Hydromechanics and Water Resources Management at ETH Zurich further progress has been achieved in the improvement of the existing hard- and software solutions. Regarding the hardware setup the acquisition system used at the ETH Zurich was upgraded from offline to online image digitization.


Data acquisition

The system used at the ETH Zurich was upgraded from offline to online image digitization. In the previous system, the image sequences were firstly recorded on analogue videotapes and digitized afterwards, while in the new system two frame grabbers (Matrox Genesis) are used to provide online digitization and storage. The length of the recorded digital image sequences is nowadays restricted by the storage device capabilities. The data rate for a 60 Hz full-frame camera with a resolution of 640 x 480 pixels is about 19 MB/sec, and hence in an experiment which lasts for 1 minute four cameras deliver a total amount of about 4.5 GB image data.

The Particle Tracking Velocimetry software performs the following tasks:

Data Processing

A crucial point is the handling of ambiguities occuring in different steps of the data processing chain:

Another important issue is an accurate calibration of the system (determination of camera exterior and interior orientations, lens distortion and further disturbances) and the exact geometric modelling ("multimedia geometry" - each beam from a particle to the sensor passes the three optical media water, glass, air with different refractive indices, which leads to a twice broken beam).


Real time image processing schemes


We organize the PTV benchmarking (open, free and user-friendly, we'll publish only what you want to be published) in order to make our algorithms validated versus each other and improve our particle tracking abilities worldwide. Write to Alex if you want to join with your own version of particle tracking software or with your data test case (e.g. that you find difficult to track or to improve).

See also