Visual odometry with Pose-graph optimization

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Hello,

I am performing visual odometry with viso2 on a webcam and want to do pose-graph optimization. I can visualise the poses and draw a trajectory with jsk_rviz_plugins. I am publishing a /base_link -> /camera tf needed for viso2. I am also performing depth estimation via deep learning in another node.

Now I want to create keyframes and do pose-graph optimization on them. I know about g2o, Ceres solver, open_karto, cartographer and openslam_vertigo, but I am unsure how to use them or where to even start with them. I found other packages that require laser data be published, but I am trying to implement monocular vSLAM w/o other sensors.

Any direction, advice or reference code would be appreciated