Vector Field Histogram
In robotics, Vector Field Histogram (VFH) is a real time obstacle avoidance algorithm proposed by Johann Borenstein and Yoram Koren in 1991.[1] The method was updated in 1998 by Iwan Ulrich and Johann Borenstein, and renamed VFH+.[2] The approach was updated again in 2000 by Ulrich and Borenstein, and was renamed VFH*.[3]
VFH
The Vector Field Histogram was developed with the aim to be computationally efficient, robust, and insensitive to misreadings. In practice, the VFH algorithm has proven to be fast and reliable, especially when traversing densely populated obstacle courses.
At the center of the VFH algorithm is the use of statistical representation of obstacles, through histogram grids (see also occupancy grid). Such representation is well suited for inaccurate sensor data, and gives the potential for the fusion of multiple sensor readings.
The VFH algorithm contains three major components:
- Cartesian histogram grid: a two-dimensional Cartesian histogram grid is constructed with the robot's range sensors, such as a sonar or a laser rangefinder. The grid is continuously updated in real time.
- Polar histogram: a one-dimensional polar histogram is constructed by reducing the Cartesian histogram around the momentary location of the robot.
- Candidate valley: consecutive sectors with a polar obstacle density below threshold, known as candidate valleys, is selected based on the proximity to the target direction.
Once the direction of the center of the selected candidate direction is determined, orientation of the robot is steered to match. The speed of the robot is reduced when approaching the obstacles head-on.
VFH+
The VFH algorithm was improved in 1998 and renamed the VFH+. Improvements include:
- Threshold hysteresis: a hysteresis increases the smoothness of the planned trajectory.
- Robot body size: robots of different sizes are taken into account, eliminating the the need to manually adjust parameters via low-pass filters.
- Obstacle look-ahead: sectors that are blocked by obstacles are masked in VFH+, so that the steer angle is not directed into an obstacle.
- Cost function: a cost function was added to better characterize the performance of the algorithm, and also gives the possibility of switching between behaviors by changing the cost function or its parameters.
References
- ^ Borenstein, J. (1991). "The vector field histogram-fast obstacle avoidance for mobilerobots". Robotics and Automation, IEEE Transactions on. 7 (3): 278–288. Retrieved 2008-06-30.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Ulrich, I. (1998). "VFH+: reliable obstacle avoidance for fast mobile robots". Robotics and Automation, 1998. Proceedings. 1998 IEEE International Conference on. Vol. 2.
{{cite conference}}: Cite has empty unknown parameter:|conferenceurl=(help); Unknown parameter|booktitle=ignored (|book-title=suggested) (help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Ulrich, I. (2000). "VFH: local obstacle avoidance with look-aheadverification". Robotics and Automation, 2000. Proceedings. ICRA'00. IEEE International Conference on. Vol. 3.
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