posest is a package for estimating camera pose from motion.
pe::PoseEstimator is the abstract class that declares the methods used for estimating a pose from frames. There are two classes that inherit from it depending on whether you have a monocular or stereo system: pe::PoseEstimator2d for monocular frames and pe::PoseEstimator3d for stereo frames.
The frames passed into these classes must have image features and descriptors already filled in. You may want to refer to the documentation for frame_common.