Vector Field Histogram
Encyclopedia
In robotics
, Vector Field Histogram (VFH) is a real time motion planning
algorithm proposed by Johann Borenstein
and Yoram Koren in 1991. The VFH utilizes a statistical representation of the robot's environment through the so called histogram grid, and therefore place great emphasis on dealing with uncertainty from sensor and modeling errors. Unlike other obstacle avoidance algorithms, VFH takes into account the dynamics
and shape of the robot, and returns steering commands specific to the platform. While considered a local path planner, i.e., not designed for global path optimality, the VFH has been shown to produce near optimal paths.
The original VFH algorithm was based on previous work on Virtual Force Field, a local path planning algorithm. After its creation in 1991, VFH was updated in 1998 by Iwan Ulrich and Johann Borenstein
, and renamed VFH+ (unofficially "Enhanced VFH"). The approach was updated again in 2000 by Ulrich and Borenstein, and was renamed VFH*. VFH is currently one of the most popular local planners used in mobile robotics, competing with the later developed dynamic window approach
. Many robotic development tools and simulation environments contain built-in support for the VFH, such as in the Player Project
.
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:
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.
functions. While simple in practice, it has been shown in experimental results that this look-ahead verification can successfully deal with problematic situations that the original VFH and VFH+ cannot handle (the resulting trajectory is fast and smooth, with no significant slow down in presence of obstacles).
Robotics
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots...
, Vector Field Histogram (VFH) is a real time motion planning
Motion planning
Motion planning is a term used in robotics for the process of detailing a task into discrete motions....
algorithm proposed by Johann Borenstein
Johann Borenstein
Johann Borenstein is an Israeli roboticist and Professor at the University of Michigan. Borenstein is well known for his work in autonomous obstacle avoidance, and is credited with the development of the Vector Field Histogram....
and Yoram Koren in 1991. The VFH utilizes a statistical representation of the robot's environment through the so called histogram grid, and therefore place great emphasis on dealing with uncertainty from sensor and modeling errors. Unlike other obstacle avoidance algorithms, VFH takes into account the dynamics
Dynamics (mechanics)
In the field of physics, the study of the causes of motion and changes in motion is dynamics. In other words the study of forces and why objects are in motion. Dynamics includes the study of the effect of torques on motion...
and shape of the robot, and returns steering commands specific to the platform. While considered a local path planner, i.e., not designed for global path optimality, the VFH has been shown to produce near optimal paths.
The original VFH algorithm was based on previous work on Virtual Force Field, a local path planning algorithm. After its creation in 1991, VFH was updated in 1998 by Iwan Ulrich and Johann Borenstein
Johann Borenstein
Johann Borenstein is an Israeli roboticist and Professor at the University of Michigan. Borenstein is well known for his work in autonomous obstacle avoidance, and is credited with the development of the Vector Field Histogram....
, and renamed VFH+ (unofficially "Enhanced VFH"). The approach was updated again in 2000 by Ulrich and Borenstein, and was renamed VFH*. VFH is currently one of the most popular local planners used in mobile robotics, competing with the later developed dynamic window approach
Dynamic window approach
In robotics, the dynamic window approach is a real-time collision avoidance strategy developed by Dieter Fox, Wolfram Burgard, and Sebastian Thrun in 1997. Unlike other avoidance methods, the dynamic window approach is derived directly from the dynamics of the robot, and is especially designed to...
. Many robotic development tools and simulation environments contain built-in support for the VFH, such as in the Player Project
Player Project
The Player Project is a project to create free software for research into robotics and sensor systems . Its components include the Player network server and Stage and Gazebo robot platform simulators...
.
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 sonarSonarSonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
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 hysteresisHysteresisHysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
increases the smoothness of the planned trajectory. - Robot body size: robots of different sizes are taken into account, eliminating the need to manually adjust parameters via low-pass filterLow-pass filterA low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
s. - 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.
VFH*
The VFH* improves upon the original VFH algorithms by explicitly dealing with the shortcomings of a local planning algorithm, in that global optimality is not ensured. In VFH*, the algorithm verifies the steering command produced by using the A* search algorithm to minimize the cost and heuristicHeuristic
Heuristic refers to experience-based techniques for problem solving, learning, and discovery. Heuristic methods are used to speed up the process of finding a satisfactory solution, where an exhaustive search is impractical...
functions. While simple in practice, it has been shown in experimental results that this look-ahead verification can successfully deal with problematic situations that the original VFH and VFH+ cannot handle (the resulting trajectory is fast and smooth, with no significant slow down in presence of obstacles).