SLAM Summer School 2006Dr. Stefan Williams1 CAS Marine Systems Stefan Williams, Oscar Pizarro, Ian...
-
date post
19-Dec-2015 -
Category
Documents
-
view
214 -
download
0
Transcript of SLAM Summer School 2006Dr. Stefan Williams1 CAS Marine Systems Stefan Williams, Oscar Pizarro, Ian...
Dr. Stefan Williams1 SLAM Summer School 2006
CAS Marine SystemsStefan Williams, Oscar Pizarro, Ian
Mahon, Paul Rigby, Matthew Johnson-Roberson
ARC Centre of Excellence for Autonomous Systems
School of Aerospace, Mechanical and Mechatronic Engineering
The University of Sydney
Dr. Stefan Williams2 SLAM Summer School 2006
Overview
• Unmanned Underwater Vehicles
• Reef Monitoring
• Navigation Sensors
• Terrain Aided Navigation
• SLAM
• Classifications
• Future Challenges
• Conclusions
Dr. Stefan Williams3 SLAM Summer School 2006
Unmanned Underwater Vehicles (UUVs)
• Constraints• No GPS• Low cost IMU• Unstructured
Terrain
• Research Challenges• Sensing and
Perception• Localisation and
Mapping• Control
Odyssey AUV (Image courtesy of MIT)
ROV Tiburon (Image courtesy of MBARI)
Phoenician wreck mosaick (Image courtesy of WHOI)
Dr. Stefan Williams4 SLAM Summer School 2006
Reef Monitoring
• This project is developing algorithms and methods for modelling marine environments
• Long term goals are to provide a set of tools to support research into the ecologically sustainable use and protection of tropical coral reefs and other marine habitats
Dr. Stefan Williams5 SLAM Summer School 2006
Reef Monitoring
• Recently returned from deployment at Capricorn Bunker Reef Group in the Southern GBR
• Deployed AUV at numerous locations to evaluate performance of system and collect data sets
• 21 data sets collected undertaking a variety of mission profiles
One Tree Island
Fitzroy Reef
Dr. Stefan Williams6 SLAM Summer School 2006
Biodiversity Assessment
• AIMS are currently conducting biodiversity assessment in collaboration with the Western Australian Museum off the North West Cape
• Techniques include dredge sleds, drop cameras and towed video sleds
• Particular focus on sponge habitats beyond diver depths
• Assessment for designation of Marine Sanctuaries
Dr. Stefan Williams7 SLAM Summer School 2006
Surveys off Ningaloo Reef
• Invited by AIMS to undertake surveys off the coast near Ningaloo Reef
• Surveys of back reef and sponge beds in up to 80m depth targeting areas based on Mandu Roughness Values shown
Ningaloo Reef
Dr. Stefan Williams8 SLAM Summer School 2006
The AUV platform
• Fully autonomous operation, no tether
• Control of vehicle performed using on-board computer
• Sensors include • Sonar (imaging and
fwd obstacle avoidance)
• Vision (stereo)• DVL• Compass• Pressure
• Mission Time ~4 hours (up to 8 hours with current housing)
Dr. Stefan Williams9 SLAM Summer School 2006
Vehicle Specifications
Vehicle Specifications
Depth rating 700m
Size 2.0 m(L) x 1.5 m(H) x 1.5 m(W)
Mass 200kg
Maximum Speed 1.2 m/s
Batteries 800 Wh Li-ion pack
Propulsion 3x150 W brushless DC thrusters
Navigation
Attitude/Heading Tilt (±0.5o), Compass (±2 o)
Depth Paroscientific pressure sensor, (0.01 %)
Velocity RDI Navigator ADCP (1-2mm/s)
Altitude RDI Navigator
USBL TrackLink 1500 HA (0.2m range, 0.25 o)
Optical Sensing
Camera Proslica 12bit 1360x1024 CCD
Lighting 2 x 200 Ws strobe
Separation ~1 m between camera and light
Acoustic Sensing
Imaging sonar Tritech Seaking
Obstacle Avoidance lmagenex 852 Echo Sounder
Other Sensors
CT Seabird 37SBI
Dr. Stefan Williams10 SLAM Summer School 2006
AUV Navigation
• A common navigation sensor used in most commercial AUV’s and many ROV’s is the Doppler Velocity Log (DVL)
• A DVL transmits 3 or 4 sonar beams downward from the AUV to measure the speed along and across the AUV track
• The AUV controller integrates heading, attitude and velocity into a dead-reckoned position estimate
Dr. Stefan Williams11 SLAM Summer School 2006
AUV Navigation
• Both GPS and acoustic positioning systems can be used to assist in determining AUV position. There are several methods for this including:
• Long Baseline Systems (LBL)
• Short baseline systems (SBL)
• Ultra short baseline system (USBL)
Dr. Stefan Williams12 SLAM Summer School 2006
AUV Navigation
• The ultrashort baseline system (USBL) requires only one transducer to be installed.
• This makes the ultrashort baseline system more portable
Dr. Stefan Williams13 SLAM Summer School 2006
DVL and USBL Performance
• Data from a recent mission illustrates the overlapping grid patterns used for dense habitat modelling
Dr. Stefan Williams14 SLAM Summer School 2006
DVL and USBL Performance
• Calibration of DVL and compass results in significantly improved error characteristics (on the order of 2% of distance travelled)
• Also working on methods for automatic calibration of vehicle and tracking sensors
Dr. Stefan Williams15 SLAM Summer School 2006
Terrain Aided Navigation
• Terrain elevation maps available for some deployment areas
• Observations of altitude can be used to bound likely position of the vehicle
Dr. Stefan Williams16 SLAM Summer School 2006
Laser Airborne Depth Sounder (LADS)
• Can be deployed in suitable conditions where water depth is 2-50m
• The infra-red component reflects from the surface
• The green component penetrates the water and reflects from the sea floor
• Depth determined from difference between the two beams
Dr. Stefan Williams17 SLAM Summer School 2006
Laser Airborne Depth Sounder (LADS)
• LADS very suitable suited for reef environments
• We have data sets available for GBR
• Can be as accurate as +/-5m horizontally +/- 0.5m depth
Dr. Stefan Williams18 SLAM Summer School 2006
Sydney Harbour Demonstrations
• Sydney Harbour presents an ideal environment in which to validate these algorithms
• Detailed bathymetric maps of the harbour are available
Dr. Stefan Williams19 SLAM Summer School 2006
Sydney Harbour Bathymetry
• Sydney Harbour Bathymetry from DSTO Shallow Water Survey
• Bathymetric data collected using multi beam echo sounder
• Resolution of 1m over extent of inner harbour
Darling Harbour
Harbour Tunnel
Dr. Stefan Williams20 SLAM Summer School 2006
Ship transect
• Ship data from DSTO, including GPS position and depth soundings taken at 5s intervals, during transect of the Harbour
• Particle based localisation and tracking of ship using depth soundings has been demonstrated using logged data
Dr. Stefan Williams23 SLAM Summer School 2006
The SLAM Problem
EstimatedLandmark
TrueLandmark
True Vehicle Path
EstimatedVehicle Path
CorrelatedLandmark Errors
Simultaneous Localisation and Map Building (SLAM)
Start at an unknown location with no a priori knowledge of landmark locations
From relative observations of landmarks, compute estimate of vehicle location and estimate of landmark locations
While continuing in motion, build complete map of landmarks and use these to provide continuous estimates of vehicle location
Dr. Stefan Williams24 SLAM Summer School 2006
The Estimation Process
Recursive three stage update procedure using Extended Kalman Filter (EKF)
PredictionPrediction
– Use vehicle model to Use vehicle model to predict vehicle positionpredict vehicle position
ObservationObservation
–Take feature observation(s)Take feature observation(s)
UpdateUpdate
–Validated observations Validated observations used to generate optimal used to generate optimal estimateestimate
–Initialise new targetInitialise new target
F0
0xv
Vehicle Path
0x2
0x3
0x1
0x4
F0
0xv
0x2
0x3
0x1
0x4
Vehicle Path
F0
0xv
0x2
0x3
0x1
0x4
Z1
Z2
Z3
Z4
Vehicle Path
F0
0xv
0x2
0x3
0x1
0x4
0x6
0x5
Vehicle Path
Dr. Stefan Williams25 SLAM Summer School 2006
SLAM
1. Initialize vehicle at origin
2. Take sonar observation of Range Bearing
3. Initialize estimate of features and project into visual frame
4. Identify visual feature within sonar footprint
5. Track visual features using KLT and provide elevation azimuth observations to filter
Dr. Stefan Williams26 SLAM Summer School 2006
Fusing Vision and Sonar
• Using the sonar returns to initialise visual features
• Features are then tracked from frame to frame using KLT
• Observations provided to SLAM algorithm to build terrain model and estimate vehicle motion
• KLT features are not stable over long term
Dr. Stefan Williams27 SLAM Summer School 2006
Terrain Model
• Sonar returns outside of visual frames are used to generate a coarse surface map
• Visual frames are projected onto surface
• Correspondence at seams suggests that algorithm is performing well
• Resulting terrain model
Dr. Stefan Williams29 SLAM Summer School 2006
Stereo Imaging
• High resolution stereo pairs allow local surface to be reconstructed
• Alternatively, features in images can be identified and position relative to vehicle computed
• Developing techniques for integration into SLAM framework
Dr. Stefan Williams35 SLAM Summer School 2006
Terrain Classification
• Techniques for automatic terrain classification
• Combined with terrain models provide a mechanism for estimating cover
• Preliminary work looked at the use of Gray Scale Histograms and mean RGB colour
Dr. Stefan Williams36 SLAM Summer School 2006
Terrain Classification
• Selection of a richer description of texture is required
• Gabor filter is used a varying scales and orientation to identify patches of coral, sand and other terrain in images
• Investigating combination of visual and sonar data for classification
Dr. Stefan Williams38 SLAM Summer School 2006
• Autonomous Systems Roles:• Wide-Area
Surveillance• Situational
Awareness• Air/Land/Sea
Operations • Tactical Strike• Mine Hunting• Littoral Zone Support
and Sensor Payload Delivery
• Research Challenges:• Multi-Sensor Data
Fusion• Multiple Platform
Control• Autonomous
Operations• Systems of Systems
Future Challenges: Defence Applications
Dr. Stefan Williams39 SLAM Summer School 2006
Future Challenges: Integrated Ocean Observatories
• Autonomous Systems Roles:• Wide-Area Surveillance• Situational Awareness• Air/Land/Sea Operations
• Research Challenges:• Multi-Sensor Data
Fusion• Modelling Ocean
Processes• Multiple Platform
Control• Autonomous Operations• Systems of Systems
Dr. Stefan Williams40 SLAM Summer School 2006
• Autonomous Systems Roles:• Exploration• Mapping• Extraction
• Research Challenges:• Multi-Sensor
Data Fusion• Adaptive
Sensing
Future Challenges: Resource Exploration
Dr. Stefan Williams41 SLAM Summer School 2006
Conclusions
• Terrain aided navigation is feasible• Extension to unstructured terrain
map building on Autonomous Underwater Vehicle (AUV)
• Deployment in various fielded situations
• Applications• Ecological Monitoring• Mineral Exploration• Mine Hunting• Littoral Zone Support and Sensor
Payload Delivery
Dr. Stefan Williams42 SLAM Summer School 2006
Acknowledgements
• This work is supported in part by the Australian Research Council (ARC) and the New South Wales Government
• Additional funding has been received from our industry partners, including• BAe Systems ATC• Sonartech Atlas• The Great Barrier Reef Research
Foundation• The Commonwealth of Australia• DSTO