Multi-Layered Navigation Meshes

Virtual characters often need to plan visually convincing paths through a complicated environment. For example, a traveler may need to walk from an airport entrance to a staircase, descend the staircase, walk to a shuttle, ride the shuttle to a destination, ride an elevator back to the ground floor, and finally move on the ground floor again to reach the desired airplane. Most previous research only supports path planning in a single plane because the underlying data structures are two-dimensional. The goal of this paper is to permit visually convincing paths to be efficiently computed in a multi-layered environment such as an airport or a multistorey building. We describe an algorithm to create a navigation mesh, and our implementation demonstrates the feasibility of the approach. A multi-layered environment is represented by a set of two-dimensional layers and a set of connections. Each layer is a collection of two-dimensional polygons that all lie in a single plane, and each connection provides a means of moving between layers. We first compute the traditional medial axis of each twodimensional layer in the environment. The connections are then used to iteratively merge this collection of medial axes into a single data structure. By adding a linear number of line segments that connect the medial axis to the nearest obstacles, we obtain a navigation mesh that mathematically describes the walkable areas in a multi-layered environment. This mesh can easily be input into existing planners to generate visually convincing paths for thousands of characters in real-time.