  The Dubins path problem had enormous applications in path planning for
autonomous vehicles. In this paper, we consider a generalization of the Dubins
path planning problem, which is to find a shortest Dubins path that starts from
a given initial position and heading, and ends on a given target circle with
the heading in the tangential direction. This problem has direct applications
in Dubins neighborhood traveling salesman problem, obstacle avoidance Dubins
path planning problem etc. We characterize the length of the four CSC paths as
a function of angular position on the target circle, and derive the conditions
which to find the shortest Dubins path to the target circle.
