sentences:  This approach requires that the 3D data is organized by a projection to a two-dimensional grid and assumes that the data is spatially smooth across neighboring grid cells with the exception of object boundaries.These assumptions are valid when dealing with 3D sensor data in applications such as surveying, robotics and stereo vision but may not hold for unorganized data in general.In practice this technique has an average search time of "O"("1") or "O"("K") for the "k"-nearest neighbor problem when applied to real world stereo vision data.