Absolute scale estimation for underwater monocular visual odometry based on 2-D imaging sonar

In this paper, the scale ambiguity in underwater monocular visual odometr y is solved with 2-D sonar measure-ments obtained from three viewpoints. Each measurement value is formulated as geometrical constraint and the recovered scale can be expressed in closed-form. Different from the existin g method which assumes the features being on the same plane in order to meet the pre-condition of quasi-homography transformation, ou r method allow s the observation points to be distributed spatially (not limited to a plane), thus extending the proposed method to more general application environments. An error contribution criterion of sonar measurement is proposed to weight the constraints, which f urther reduces the influence of noisy input. Experiments are performed in both simulated and real environments. For nonplanar case, the proposed method gives improved accuracy after employing constraint weighting. As for planar case, ou r method achieves comparable accuracy to the existing method, while the time consumption is much lower.

Automated summary

This paper solves the scale ambiguity in underwater monocular visual odometry by using 2D sonar measurements from three viewpoints. The proposed method allows spatial distribution of observation points, extending its applicability to more general environments. A constraint weighting approach is introduced to reduce the influence of noisy input. Experimental results demonstrate the improved accuracy and lower time consumption of the proposed method.