  This letter suggests an integrated approach for a drone (or multirotor) to
perform an autonomous videography task in a 3-D obstacle environment by
following a moving object. The proposed system includes 1) a target motion
prediction module which can be applied to dense environments and 2) a
hierarchical chasing planner based on a proposed metric for visibility. In the
prediction module, we minimize observation error given that the target object
itself does not collide with obstacles. The estimated future trajectory of
target is obtained by covariant optimization. The other module, chasing
planner, is in a bi-level structure composed of preplanner and smooth planner.
In the first phase, we leverage a graph-search method to preplan a chasing
corridor which incorporates safety and visibility of target during a time
window. In the subsequent phase, we generate a smooth and dynamically feasible
path within the corridor using quadratic programming (QP). We validate our
approach with multiple complex scenarios and actual experiments. The source
code can be found in https://github.com/icsl-Jeon/traj_gen_vis
