Fig. 1. Overall measurement chart. (a) Overall scheme diagram ; (b) schematic diagram of refractive endoscope device imaging

Fig. 2. Schematic diagram of measurement principle. (a) Axial expansion diagram of real barrel; At depth (b) h₁; (c) h₂ of barrel, with the 6th rifling as tracking target, take image in circular domain with a radius of r

Fig. 3. Flow chart of twist rate measurement of barrel based on panoramic imaging

Fig. 4. Process of panoramic image enhancement algorithm based on polar coordinates

Fig. 5. Schematic diagram of polar coordinate template matching

Fig. 6. Functional diagram of sector window

Fig. 7. Process of generating simulation data

Fig. 8. Localization result images of tracking and positioning algorithm. (a) Localization results of tracking and positioning algorithm for simulation data 1; (b) localization results of tracking and positioning algorithm for simulation data 2

Fig. 9. Actual measurement scenario of barrel twist angle

Fig. 10. Partial result images of measurement experimental algorithm

Fig. 11. Experimental diagram of barrel twist rate measurement. (a) Actual measurement experimental results of barrel twist rate; (b) absolute error interval chart of actual measurement experimental results of barrel twist rate