Transcript Poster

Cooperative Multi-Robot Systems
Vision-based 3-D Mapping using Information Theory
Rui Rocha, M.Sc., Jorge Dias, Ph.D., Adriano Carvalho, Ph.D.
• Aim
– Take advantage from intelligent cooperation between mobile robots, so as to
build fast and accurate 3-D maps of unknown environments, through efficient
information sharing based on information utility.
• A multi-robot system may be more efficient, reliable and robust than a single robot
solution.
• The space and time distribution of multiple robots allow them to accomplish the mapping
mission in less time.
• If there is an overlap in individual robots capabilities (redundancy), the failure of any
particular robot does not compromise the overall mission accomplishment.
• It robots with different, complementary and specialized skills are used, they may
overcome their individual limitations (e.g. different sensors, locomotion, etc.) and
increase the system’s robustness.
• Background
– Some authors have already addressed the problem, though there are important
limitations that we intend to overcome:
• Most approaches are restricted to 2-D indoor, flat maps and use a single robot;
• There are some probabilistic approaches (e.g. occupancy grids), but do not minimize
inter-robot communication when fusing the maps from different robots;
• Very few authors used entropy to formulate the expected information gain of control
actions – focused on coordination or not viable in real-time.
• Studies about multi-robot communication focus mainly on the communication structure
rather than on the communication contents.
• They are tailored in indoor and flat environments; our approach is aimed at using a team
of cooperating mobile robots to build 3-D coverage maps of environments not
necessarily flat.
– There is no a principled mechanism to assess information utility, which might be
used to support efficient multi-robot communication.
• Using efficiently communication resources is crucial to scale up MRS for teams of many
robots.
• Research issues
– Grid-based probabilistic maps [3]
• The occupancy of each cell – voxel – is modeled through a continuous random variable,
ranging from empty cell to fully occupied voxel.
• Compact representation: only two parameters are stored for each voxel.
• Explicit representation of uncertainty through the entropy concept.
z
• Straightforward update of the voxel’s coverage belief through a Bayes Filter.
y
– Entropy gradient-based exploration [3]
x
{W}
tk=1938 s
H(C | Mk)=70059 bits
tk=763 s
H(C | Mk)=91179 bits
• Reformulation of frontier-based exploration: frontier voxels have maximum entropy
gradient.
t
((( )))
Communication
– Distributed architecture model [1]
Measurements
Memory
• Each robot is capable of building a 3-D map, though it is altruistically committed to share
useful measurements with its teammates, who also may provide it with useful data.
– Entropy-based measure of information utility
tk=9289 s
H(C | Mk)=28691 bits
Map Update
U
[1]
3-D Map
• Used to support efficient information sharing.
• Sensory data is as useful as it contributes to improve the robot’s map.
– Coordinated exploration based on the minimization of mutual information
Survey
Controller
(.,.)
[2]
• Each robot avoids to sense regions that are already being sensed by other robots.
Sensor
Localization
• Minimize robots’ interference: partial occlusions and not reachable exploration
viewpoints.
Robot’s platform
• Selected publications
[1] R. Rocha, J. Dias and A. Carvalho. Cooperative multi-robot systems: a study of vision-based 3-D mapping
using information theory. In Proc. of Int. Conf. on Robotics and Automation (ICRA’2005), Barcelona, Spain,
pages 386-391, Apr. 2005.
[2] R. Rocha, J. Dias and A. Carvalho. Entropy gradient-based exploration with cooperative robots in 3-D
mapping missions. In Proc. of ICRA’2005 Workshop on Cooperative Robotics, IEEE Int. Conf. on Robotics
and Automation, Barcelona, Spain, Apr. 2005.
[3] R. Rocha, J. Dias, and A. Carvalho. Exploring Information Theory for Vision-Based Volumetric Mapping. In
Proc. of IEEE/RSJ Int. Conf. on Intelligent Robots and Systems (IROS’2005), Edmonton, Canada, pages
2409-2414, 2-6 Aug. 2005.
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Contact Person:
Rui Rocha
Email: [email protected]
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Mobile Robotics Laboratory
Institute of Systems and Robotics
ISR – Coimbra
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Sep. 2005