PTV

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Particle Tracking Velocimetry Software

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Free download, documentation and user group at openPTV

Introduction

The three-dimensional particle tracking velocimetry (3D-PTV) is a nonintrusive measurement technique which allows for the determination of velocity and velocity derivatives in turbulent flows. It is based on the visualization of a flow seeded with small neutrally buoyant particles (flow tracers) 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 (IGP) in cooperation with the Institute of Environmental Engineering (before 01.01.06 Institute of Hydromechanics and Water Resources Management, IHW) at ETH Zurich led to an operational and reliable measurement tool used in experimental fluid mechanics.  Recently further progress has been achieved in the improvement of the existing hard- and software solutions.

Tasks

The Particle Tracking Velocimetry software performs the following tasks:

  • Calibration of the multi-camera 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).
  • Image preprocessing: perform highpass filtering due to non-uniformities in the background illumination.
  • Detect particles in the images by a modified thresholding operator, localize particles with subpixel accuracy by a centroid operator.
  • Establish stereoscopic correspondences.
  • Determine 3-D particle coordinates.
  • Storage of all relevant object and image space information.
  • Perform tracking in 2-D image and 3-D object space.

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

  • Particles may overlap in the images. For that reason a modified thresholding/centroid operator was developed searching for local maxima in the images and dividing particle images at local minima under certain conditions.
  • Due to the fact that particle images cannot be distinguished by features like size, shape or color, the only criterion for the establishment of stereoscopic correspondences is the epipolar line. Ambiguities occur when multiple candidates are found in a search area defined by the epipolar line. These ambiguities can only be solved if a third (or even a fourth) camera is being used.
  • Ambiguities may also occur in the tracking procedure. Criteria like local correlation and smoothness of the velocity field are employed to solve these criteria.

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DISCLAIMER OF WARRANTY:
Since the Software is provided free of charge, the Software is provided on an AS IS basis, without warranty of any kind, including without limitation the warranties of merchantability, fitness for a particular purpose and non-infringement. The entire risk as to the quality and performance of the Software is borne by you. Should the Software prove defective, you assume the entire cost of any service and repair.

LIMITATION OF LIABILITY: UNDER NO CIRCUMSTANCES AND UNDER NO LEGAL THEORY, TORT, CONTRACT, OR OTHERWISE, SHALL THE AUTHORS BE LIABLE TO YOU OR ANY OTHER PERSON FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OF ANY CHARACTER INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF GOODWILL, WORK STOPPAGE, COMPUTER FAILURE OR MALFUNCTION, OR ANY AND ALL OTHER COMMERCIAL DAMAGES OR LOSSES.

 
 
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Tue Feb 28 05:08:12 CET 2017
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