| ... | @@ -22,12 +22,19 @@ There are two choices to record a image for [position detection](https://git-xen |
... | @@ -22,12 +22,19 @@ There are two choices to record a image for [position detection](https://git-xen |
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* The second choice is to use another light source with different wavelength without the *Polarizer*, which is the polarizer between the light source and the sample. An example setup is shown in the left figure below (from [*J. E. Kollmer et al.*](#https://arxiv.org/abs/1807.01786)). An example image taken from this setup is shown in the middle figure below (from [*J. E. Kollmer et al*](https://arxiv.org/abs/1807.01786)). Only one image is enough for both position detection and the photoelastic fringes recording. The red channel of the middle image can be used for the position detection and the green channel of the middle image can be used for the photoelastic stress analysis. This method saves the number of images needed to record in one experiment, which is of great practical importance: typical DSLR camera encounters shutter problems after around 100,000 images taken.
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* The second choice is to use another light source with different wavelength without the *Polarizer*, which is the polarizer between the light source and the sample. An example setup is shown in the left figure below (from [*J. E. Kollmer et al.*](#https://arxiv.org/abs/1807.01786)). An example image taken from this setup is shown in the middle figure below (from [*J. E. Kollmer et al*](https://arxiv.org/abs/1807.01786)). Only one image is enough for both position detection and the photoelastic fringes recording. The red channel of the middle image can be used for the position detection and the green channel of the middle image can be used for the photoelastic stress analysis. This method saves the number of images needed to record in one experiment, which is of great practical importance: typical DSLR camera encounters shutter problems after around 100,000 images taken.
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## 3. Rotation tracking and light color
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## 3. Rotation tracking and light color
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The rotation of the discs can be tracked by drawing a ultra-violet(UV) sensitive bar on them. Tracking the rotation of the bars is equal to tracking the rotation of the particles. Those labels are only visible under UV light so they will not interference with the photoelastic fringes. The right figure below shows an image taken under UV light that shows all the UV bars on them. (from [*J. Ren et al.*](#https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.018302)) The UV bars are plotted using [*MAR-C0 Invisible Blue UV Pen from Risk Reactor*](#http://www.riskreactor.com/invisible-uv-pens/mar-c0-invisible-blue-uv-marking-pens/) (left figure). UV labels can also be used to help finding the center of non-spherical particles, where Hough transformation for particle boundary detection does not work.
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The rotation of the discs can be tracked by drawing a ultra-violet(UV) sensitive bar on them. Tracking the rotation of the bars is equal to tracking the rotation of the particles. Those labels are only visible under UV light so they will not interference with the photoelastic fringes. The right figure below shows an image taken under UV light that shows all the UV bars on them. (from [*J. Ren et al.*](#https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.018302)) The UV bars are plotted using [*MAR-C0 Invisible Blue UV Pen from Risk Reactor*](#http://www.riskreactor.com/invisible-uv-pens/mar-c0-invisible-blue-uv-marking-pens/) (left figure). UV labels can also be used to help finding the center of non-spherical particles, where Hough transformation for particle boundary detection does not work.
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