Finally, scale space analysis method is used to refine each point in the coarse centerline in its cross-section plane. Thus, an accurate centerline is obtained.
The image subtracting method and the point to arc projection extremum algorithm can derive the pointer and scale marks quickly, and separate the long and short graduation line.
The principle, method, experiment facilities and result of the realization of the International Temperature Scale of 1990(ITS\|90) above silver freezing point at NIM are described.