# Pathfinding. “PathEngine is a sophisticated middleware tool- kit for the implementation of intelligent agent movement, built around an advanced implementation.

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Pathfinding

“PathEngine is a sophisticated middleware tool- kit for the implementation of intelligent agent movement, built around an advanced implementation of points-of-visibility pathfinding on 3D ground surfaces.” ~www.pathengine.com/overview

SDK Licensing options

Cheaper Options Breadth-First Search Dijkstra’s Algorithm Best-First Search A* Search

Breadth-First Search Examines all paths of cost 1, then 2, and so on until it finds the goal. Guaranteed to find the shortest path Very slow

Dijkstra’s Algorithm Selects closest unprocessed node from the start, and updates its value, and that of its neighbors. Nodes are valued by the distance from the start.

Best-First Search Similar to Dijkstra’s Algorithm, but uses a heuristic to determine the value of node. Main disadvantage is that is does not account well for terrain that is slower.

A* Search Very similar to a Breadth-First Search. Orders nodes to search not just by distance from start node, but also by a “heuristic” or a estimate cost remaining to the end point.

A* Search The cost of a node is defined as f(n) = g(n) + h(n) where g(n) is the distance traveled from the start h(n) is the heuristic, the estimated distance to the end node

A* Heuristic The heuristic is an estimate for the remaining cost to the end point This estimate should be a close as possible to the actual cost, but never higher. For a grid of squares, the heuristic is usually the number of squares in between the current node and the end node. (note this is different from the Euclidean distance)

A* Search Examples

A* Considerations You must define how diagonal squares work with map grids. If movement is continuous, consider multiplying the cost of diagonal movement by √ 2 Defining an upper bound cutoff can prevent the search from taking too long.

References Path Engine http://www.pathengine.com/index.php Smart Moves: Intelligent Path-Finding http://www.gamasutra.com/features/19990212/sm_01.htm Ogre Articles and Resources http://www.ogre3d.org/wiki/index.php?title=ArticlesAndSources&redirect=no Pathfinding using A*-algorithm http://www.cs.helsinki.fi/u/apipulkk/astar/index.html

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