Effect of imaging distance on image texture of sand in PIV analysis

Michael G. Dutton, A. Neil, W.A. Take

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Laboratory Testing

ABSTRACT: This paper presents the results of an investigation into the impact of distance between the camera and the target on the image texture and the measurement accuracy of a particle image velocimetry (PIV) analysis for two types of sand. To obtain an optimal result from the PIV technique the results indicate that a certain level of image texture, quantified by the mean intensity gradient (MIG), is required. It was found that on a global scale, the optimal texture occurred at a similar working distance for the two sands, owing to the similarity in the grain size; however, the MIG was larger for the synthetic olivine due to its colour variation. Results show that decreasing texture of individual subsets was more likely to lead to errors in the analysis. Furthermore, subsets with adequate MIG values can still produce significant errors in one direction versus the other suggesting the need for a better texture descriptor. It is shown that correct placement of the camera will help to reduce the likelihood of measurement errors.

RÉSUMÉ: Cet article présente les résultats enquête précision de sable basé sur la vélocimétrie Pour obtenir un résultat idéal en utilisant la technique PIV les résultats la doit être à un certain niveau. Il a été constaté que sur une échelle mondiale, la texture idéale a été produite avec une distance similaire pour les deux types de sable grâces aux similarités olivine synthétique à cause des variations de ses couleurs. réduisant la texture des sous-ensembles individuels est plus susceptible aux erreurs. En outre, les sous-ensembles avec des valeurs de MIG adéquates peuvent comme même produire des erreurs significatives dans un sens par rapport à suggérant une nécessité pour un meilleur descripteur de texture. probabilité des erreurs de mesures.

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