English: Illustration of Dijkstra's algorithm. The graph is created by uniform square discretization of a 2-dimensional planar region, placing a node in each discretized cell, and connecting each node with its 8 neighbors using bidirectional edges. Cost of edges are same as their Euclidean lengths. The gray shape represents an obstacle. The filled circles in red & green represent expanded nodes (nodes in closed set). The color indicate the distance (in the graph) of a node from the start node (red: lower, green: higher). The empty nodes with blue boundary are the ones in open set. The nodes of the graph are generated on the fly, and nodes falling inside the obstacle are discarded as inaccessible. Note that Dijkstra's is a special case of the A* search algorithm when the heuristic is identically 0. Note how the nodes are expanded almost uniformly in all directions. The number of nodes expanded is significantly higher when compared with the same search problem solved using A* search algorithm. Created using YGSBPL graph-search library and OpenCV.