A method of navigational ray casting in a computing device includes: obtaining a distance map having a plurality of cells representing respective sub-regions of an environment containing obstacles; wherein each cell defines a minimum obstacle distance indicating a distance from the corresponding sub-region to a nearest one of the obstacles; selecting an origin cell from the plurality of cells, and setting the origin cell as a current cell; selecting a ray cast direction for a ray originating from the origin cell; retrieving the minimum obstacle distance defined by the current cell; selecting a test cell at the minimum obstacle distance from the current cell in the ray cast direction; determining whether the test cell indicates the presence of one of the obstacles; and when the determination is affirmative, determining a total distance between the origin cell and the test cell.