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Accelerometer-based User Interfaces for the Control of a Physically Simulated Character Takaaki Shiratori Jessica K. Hodgins Carnegie Mellon University
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Physical Simulation in Games Controllable interface for physically simulated character Jurassic Park: Trespasser, 1998 2 Simulation for everything. - Very limited. Little Big Planet, 2008 1 Simulation ONLY for passive objects. - Effective! 1 http://www.littlebigplanet.com/ 2 http://www.mobygames.com/game/trespasser-jurassic-park
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Half speed Physically Simulated Character Natural-looking motion. Natural responses to environment/disturbance.
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Natural-looking motion. Natural responses to environment/disturbance. Hard to control due to delayed response (anticipation). Physically Simulated Character Walk Jump – Our Hypothesis – Performing similar actions might make the delay seem intuitive. 0 1.0 2.0 3.0 0 1 2 3 4 5 Speed [m/s] Time [sec] Walk Jump Anticipation
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Our Approach Performance interface: User Imitates character’s motion with Wiimotes. – Wrist interface – Arm interface – Leg interface Test our hypothesis about delay with user study. Leg interface
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Accelerometer IR sensor $40 / unit 30 million copies Wiimote TM 1 http://www.gizmag.com/go/6773/ 2 http://www.cs.cmu.edu/~johnny/projects/wii/ 12
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Related Work Interface for controlling a character – Physically simulated character in 2D. Virtual navigation – Control “view point”. Wii games – Either dynamic or static measurement. [Johnson et al. 1999] [van de Panne and Lee 2003][Slyper and Hodgins 2008] [Chai and Hodgins 2005] [Templeman et al. 1999] [Razzaque et al. 2002] [Nintendo 2006][Nintendo 2007][Ubisoft 2007]
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Overview 2-3 Wiimotes Physically simulated motion Mapping Controller selection Parameter change Acceleration Analysis Amp., Mean, Inclination Moving or not, Freq., Phase Motion controller (walk, run, jump, step) Physical Simulation
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Overview 2-3 Wiimotes Physically simulated motion Mapping Controller selection Parameter change Acceleration Analysis Amp., Mean, Inclination Moving or not, Freq., Phase Motion controller (walk, run, jump, step) Physical Simulation
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Focus on periodicity of character’s motion. User Input Walking RunningJumping Basic command: swing Wiimotes In-phase Out-of-phase
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Acceleration Analysis Features Yes No Raw acceleration Frequency Amplitude Inclination Phase diff. L R Mean Kalman filter Moving? Variance
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Frequency Auto-correlation function a : acceleration data T : current time t p : window size
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Acceleration Analysis Features Yes No Raw acceleration Frequency Amplitude Inclination Phase diff. L R Mean Kalman filter Moving?
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Phase Difference Cross-correlation function a : acceleration data a : mean acceleration T : current time t p : window size
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Acceleration Analysis Features Yes No Raw acceleration Frequency Amplitude Inclination Phase diff. L R Mean Kalman filter Moving?
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Inclination Estimation If Wiimote is not moving, If Wiimote is moving, Wiimote’s local coordinate. x y z g t acc. x t mean
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Overview 2-3 Wiimotes Physically simulated motion Mapping Controller selection Parameter change Acceleration Analysis Amp., Mean, Inclination Moving or not, Freq., Phase Motion controller (walk, run, jump, step) Physical Simulation
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Hopper Model Hip: Ball joint (3 DoFs) Knee: Slider joint (1 DoF) Simulation Rendering
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Basic Motions Stepping in place (Stopping) RunningWalkingJumping
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Consists of 3 contact states with Proportional- Derivative (PD) controller. Support foot passes under hip. Rear leg leaves ground. Swing leg contacts ground. FallRise Double Support Walking Controller [Raibert and Hodgins, 1991] Stepping-in-place controller: target velocity = 0
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Consists of 4 contact states with PD controller. Running Controller [Raibert and Hodgins, 1991] Jumping controller: both legs in phase.
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Based on the robustness of motion. Gait Transition Jumping Stepping in place WalkingRunning WalkingRunning Slow Fast
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Overview 2-3 Wiimotes Physically simulated motion Mapping Controller selection Parameter change Acceleration Analysis Amp., Mean, Inclination Moving or not, Freq., Phase Motion controller (walk, run, jump, step) Physical Simulation
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Mapping Wiimotes to Physical Simulation Wiimotes not moving. Wiimotes out of phase. Wiimotes in phase. Height: Wiimote amplitude Jumping Stepping in place WalkingRunning WalkingRunning Slow Fast Wii frequency
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Wrist Interface Imitate character’s leg motions with user’s wrists.
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Wrist Interface Imitate character’s leg motions with user’s wrists. Walking (Slow swing) Running (Fast swing) JumpingTurning
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Arm Interface Imitate arm motion of human’s biped motion. (though the character doesn’t have upper body)
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Arm Interface Imitate arm motion of human’s biped motion. (though the character doesn’t have upper body) WalkingRunningJumpingTurning
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Leg Interface Imitate character’s leg motion with user’s legs.
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Leg Interface Imitate character’s leg motion with user’s legs. Walking (Slow step) Running (Fast step) JumpingTurning
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Typical usage. Joystick Interface RightLeft Forward Run Walk Turn in place Step in place LocomotionJumping
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User Study 15 subjects. Tasks – Straight track completion. – Test track completion. Questionnaire – Fun, ease of use, stress, familiarity, immersion, how much they liked it? – Free-form questions. Courses:
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Task 1.Motion transition at line. 2.Keep straight walking/running until line. Straight Track Completion Average failure count Straight walking: All of our interfaces < Joystick
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Failure for Straight Walking Approximate motions RightLeft Forward Run Walk Turn in place Step in place Precise manipulation Wrist ArmLeg Joystick Straight walk
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Test Track Completion Simulation failureJump failureCurve failure + Time to completion Time to failure
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Result of Test Track Completion Average countTime [sec] Curve failure: Leg interface < joystick Our interfaces are easier to control than joystick.
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Result of Questionnaire “Fun”“Ease of use”“Stress” “Familiarity”“Immersion” “Like” Score
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Free-form questions: Most subjects did not complain about the delay. A few subjects complained about the delay of all interfaces (including joystick). Questionnaire Rating score: “Immersion”: Wrist, Leg > Joystick “Like”: Wrist, Leg > Joystick
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Insights from User Study Delay factors: – Acceleration analysis: 100 – 500 ms (Not included in joystick interface) – Physical simulation (anticipation): 200 – 500 ms Task completion: Easy to control: our interfaces > joystick. Questionnaire: “Immersive” and “Like”: our interfaces > joystick. Immersive performance interface might help with the delay issue.
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Competitive Game
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Conclusion Summary Performance interfaces for controlling a physically simulated character. User study mainly focusing on delay issues. – Performance interface might be able to help with delay issue. Future Work Reduce delay. – Improve acceleration analysis. Further user study. – Delay issue: Compare with data-driven control. – Other scenarios (e.g. fighting game, FPS).
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