Figure 2.

The sketch map of the pose graph. (a) is the initial pose graph obtained by VO where the blue edges are the transformations between two nearby keyframes. (b) is obtained after the closing loop detection and the red edges connect the frames satisfying the loop constraints. (c) denotes the relationship between two cameras, where black vertices are the poses of one camera and brown vertices belong to another camera, the green edge means the extrinsic parameters which can be initially set to the identity matrix.