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There are two different methods used in DAWN to calibrate powder diffraction images, Ellipse Parameter Calibration and Point Parameter Calibration. Here is a quick introduction to the calibration routine and the differences between the two methods.
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Finding points of interest (POI)
The first step in the calibration process is to find the location of points of interest marking where the diffraction rings from the standard are in the image. DAWN takes a line profile across the ring, at many points around the ring and the peak fits the profile to find the maximum. The position of the maximum, transformed back into the image co-ordinates is a point of interest. The difference between the Ellipse Parameter Calibration and Point Parameter Calibration is what is done with these POIs to calibrate the experiment.
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