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Detect and follow particles
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Most experiments study a model 2 dimensional (2D) granular system composed of circular discs as grains. While in cases of studying particle shape effect, discs are replaced by other shapes like ellipses, polygons and crosses \cite{}. With a digital camera, the first and one of the most important information that can be obtained is particle positions. Particle detection and tracking alone provide rich information such as particle configuration and flow field, and are necessary for further measurements like force-bearing contact detection and contact force calculation. In this session, a detailed description for detecting particle positions and orientations and tracking particles in high resolution images will be summarized below. In addition, in images with resolution not high enough to precisely detect particle positions, another method (PIV) will be introduced.
Most experiments study a model 2 dimensional (2D) granular system composed of circular discs as grains. While in cases of studying particle shape effect, discs are replaced by other shapes like ellipses, polygons and crosses. With a digital camera, the first and one of the most important information that can be obtained is particle positions. Particle detection and tracking alone provide rich information such as particle configuration and flow field, and are necessary for further measurements like force-bearing contact detection and contact force calculation. In this session, a detailed description for detecting particle positions and orientations and tracking particles in high resolution images will be summarized below. In addition, in images with resolution not high enough to precisely detect particle positions, another method (PIV) will be introduced.
## 1 Position detection and tracking
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### 2.1 Direct tracking
Erick track.
Once particle centers are detected, they can be tracked throughout the whole experiment. One efficient and accurate algorithm has been developed and implemented in Matlab by [John Crocker, David Grier and Eric Weeks](http://www.physics.emory.edu/faculty/weeks//idl/).
### 2.2 Measurement of the particle flow
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