| A new technique for processing ultrasonic arc maps is proposed
and compared to six existing techniques for map-building purposes.
These techniques are simple point marking along the line-of-sight,
voting and thresholding, morphological processing, Bayesian update
scheme for occupancy grids, arc-transversal median algorithm,
and triangulation-based fusion. The directional maximum technique,
newly proposed in this paper, employs directional processing to extract
the map of the environment from ultrasonic arc maps. It aims
at overcoming the intrinsic angular uncertainty of ultrasonic sensors
in map building, as well as eliminating noise and cross-talk related
misreadings. The compared techniques are implemented with a wallfollowing
motion-planning scheme for ground coverage. The comparison
is based on experimental data and three complementary error
criteria: mean absolute error, correct detection rate for full and empty
regions, and computational cost in terms of CPU time. The directional
maximum technique offers a very good compromise between mean
absolute error and correct detection rate, with a processing time less
than one-tenth of a second. Compared to the existing techniques, the
directional maximum method is also superior in range accuracy and
in eliminating artifacts, resulting in the best overall performance. The
results indicate several trade-offs in the choice of ultrasonic arc-map
processing techniques. |
