A number of navigation functions are performed on terrain navigation space. One function is to define a dynamic dangerous zone based on flight altitude by locating and aggregating a set of nodes of terrain height over a minimum flight altitude. Algorithms such as collision check, mountainous area boundary and region growing techniques are developed as basic operations for this terrain model. In addition, a visibility graph approach for dynamic route selection may be adapted to reduce the real-time computational requirements. This approach reduces the size of the search space by establishing a partial visibility graph of terrain and avoids details of the terrain, which do not influence the choice of flight path, independent of the size of the navigation space. By exploiting the multiple and variable resolution properties of Oct-tree terrain models, a series of CFIT warning functions using terrain data as reference are implemented efficiently with existing on-board terrain data resources.
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