Dear masters,How is the data in aorta_centerline and spline_centerline calculated in the ImageCPRMpper example?

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Dear masters, in the ImageCPRMpper example, there are two JSON files, aorta and split, with two arrays, position and orientation, inside. What is the relationship between the two and how is it calculated?
This is an example address：

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I found a way to collect point coordinates using vtkPaintWidget