Fig. 1. Characteristic circular target

Fig. 2. Camera imaging principle

Fig. 3. perspective projection principle

Fig. 4. Schematic projection of a circular target

Fig. 5. Variation of a₁ and a₂ lengths under perspective distortion

Fig. 6. The variation of absolute error accuracy of ellipse method

Fig. 7. Absolute error variation of different algorithms（r=15 mm）

Fig. 8. Experimental platform of spatial plane pose measurement

Fig. 9. Imaging region of camera at different object distances

Fig. 10. Experiments of absolute error based on different algorithms（r=15 mm）