A method includes obtaining an occupancy grid. The method includes generating a reference, such as a ray, on the occupancy grid. The ray originates from a location of a vehicle and extends in a direction that corresponds to a driving direction of the vehicle. The method includes identifying markers along the ray. The markers include transition markers, which indicate a first type of transition or a second type of transition. The first type of transition is from an unoccupied zone to an occupied zone. The second type of transition is from the occupied zone to the unoccupied zone. The method includes generating a representation of drivable space in real-time based on computations involving sections that are associated with the first type of transition and the second type of transition. The method includes providing guidance to the vehicle based on the representation of drivable space.