Fig. 1. Misaligned tower-shaped artefact

Fig. 2. Tower-shaped artefact proposed by Ibaraki^［22］

Fig. 3. Schematic diagram of measurement points distribution and fitting line of artefact on-machine measurement

Fig. 4. On-machine measurement strategy

Fig. 5. WCS at different angles of C-axis

Fig. 6. PGDE identification principle

Fig. 7. On-machine measurement at different angles of C-axis

Fig. 8. Identification results of 6 PDGE of C-axis

Fig. 9. Identification method based on ball-bar

Fig. 10. Comparison of test results between proposed method and ball-bar identification