Transcript Reality of virtual world

Springhead:An open source physics simulator
Advanced Topic in Intelligence Sciences
Physics simulation and character
motion generation for virtual reality

Precision & Intelligence Lab
 Shoichi Hasegawa
 http://springhead.info/~hase/
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Springhead:An open source physics simulator [email protected]
Virtual reality
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Measure input and motion of human
 Simulate virtual world
 Present stimulates to the five senses.

The stimulates imitate the real world.
Interface
Senses
Motion
Presentation
Input
Measurements
Computer
Simulation
Virtual world
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Springhead:An open source physics simulator [email protected]
What is Reality ?
Real
world → physical world
Sensation of real world
→ A world sensed by a human
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Brain in a vat. The world of “Matrix” cinema.
Human
senses the world via “five senses”
and the brain recognizes the world.
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Reality exists in human mind
Visual/Auditory/Olfactory/Gustatory
Computer
Haptic
Somatic sensations
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Springhead:An open source physics simulator [email protected]
How can we create a good virtual reality
Interface
senses
Computer
presentation
Simulation
motion
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input
measurement
Virtual world
Humans perceive the world via their senses
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Stimulus which satisfy human senses are enough.
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This fact decreases difficulty of virtual reality.
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Springhead:An open source physics simulator [email protected]
Window of senses
A
ray of light is a physical phenomena.
Human
perceives visible rays only.
We do not have to reproduce infrared or ultra violet rays
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Springhead:An open source physics simulator [email protected]
Window of senses
Human
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vision
Color and light
Three primary colors
Absorption spectrum of visual substances
on cone cells（S,M,L）and rod cells（R）of human eyes.
（Center of foveas have cone cells only. Retinas for peripheral
vision have rod cells only.）
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Springhead:An open source physics simulator [email protected]
Window of senses
Light
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Humans perceives yellow.
Light
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of wave length λ=590nm, intensity I=1.0
of λ=600nm, I=0.9 ＋ λ=546nm I=0.9
Humans perceives yellow.
Humans
can not distinguish them. They are virtually equal to
human.
We do not have to reproduce wave length
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Springhead:An open source physics simulator [email protected]
Researches for perfect virtual reality

Reproduce all senses of human same as in the real world.
Cabin at univ. Tokyo
Olfactory display
by Nakamoto lab.
Tokyo tech.
Sensics piSight HMD
2200x1200 145°x 60°
computer
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World of “The Matrix”
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SPIDAR by
Makoto Sato lab.
Tokyo tech
TorusTreadmill by Iwata lab.
Tsukuba univ.
Is is possible? Do you like such worlds ?
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Springhead:An open source physics simulator [email protected]
What is realtiy ?
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Is reproducing of all senses same as in the real world
reality ?
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If so, what is reality of novel ?
Before thinking about this problem. Let see some
virtual system (made by me).
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Springhead:An open source physics simulator [email protected]
1993 My first force feedback experience
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Large robot arm like UNC’s Grope
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I wrote some part of haptic rendering code.
This system uses FES(functional electric stimuli) to present feed
back force for each finger.
f=knd
d
n
Springhead:An open source physics simulator [email protected]
Springhead:An open source physics simulator [email protected]
1994: non-contact tracking haptic
interface
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Our haptic interfaces are heavy to drag.
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For free space: Tracking hand without contact.
Displaying object: Stop the tracking. Hand hit to the device.
Method to measure distance:
•Attach an antenna to the seat.
•Measure the impedance between hand
(surface of hunan) and sensor.
I think this is new and submit a pattent
but…
MIT media lab Fish sensor 1995
Springhead:An open source physics simulator [email protected]
Springhead:An open source physics simulator [email protected]
1995 jumping locomotion device
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Locomotion device for all direction.
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We named this device
G.O.D
Gravity On Demand
Springhead:An open source physics simulator [email protected]
Springhead:An open source physics simulator [email protected]
１９９６ Locomotion device by walking
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Walking sensation presenting device
Springhead:An open source physics simulator [email protected]
Springhead:An open source physics simulator [email protected]
１９９６ Join to Makoto Sato’s lab

I won lots to join to Sato lab.
 Sato&Koike Gp. P&I Lab, Tokyo Institute of Technology
 They research SPIDAR since 1989
Springhead:An open source physics simulator [email protected]
１９９７ Virtual Basket
My first SIGGRAPH
Springhead:An open source physics simulator [email protected]
２０００ Virtual Rubik's cube
Springhead:An open source physics simulator [email protected]
２００４ Both hand direct manipulation
Springhead:An open source physics simulator [email protected]
２００５ Virtual Canoe
Springhead:An open source physics simulator [email protected]
２００５ Virtual Canoe
Springhead:An open source physics simulator [email protected]
Hardware
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1993 ARMSII
Link and ・Gimbal mechanism
1994 ARMSIII
pantograph mechanism and ball screw
1995 G.O.D.
Electro magnetic break, rubber cords
1996 ARMSV
AC servo motors, linear rail
1997 Virtual Basket
SPIDAR with 8 motors
2000 Virtual Rubik’s Cube
SPDIAR with 24 motors
2004 Both Hand Direct Manip
SPIDAR with 8 motors
2005 Virtual Canoe
SPIDAR with 8 motors
Springhead:An open source physics simulator [email protected]
Software
1993 ARMSII
Sense8’s World Tool Kit
 1994 ARMSIII
Sense8’s World Tool Kit
 1995 G.O.D.
Super Scape’s VRT
 1996 ARMSV
Original software based on Rend386
 1997 Virtual Basket
Direct X with simple physics simulation
 2000 Virtual Rubik’s Cube
Direct3D and simple physical simulation
 2004 Both hand haptic interaction
Original physics engine based on Volumetric Penalty Method
 2005 Virtual Canoe
Direct3D and Original Fluid simulation
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Springhead:An open source physics simulator [email protected]
Realities for content
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VR
Levels of Realtiy
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Reality of sensation
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Resolution, Field of view，Color fidelity …
Reality of image
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picture： number of polygons，lighting models …
Moving picture：Mocap，animation …
Large distance
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Reality of movie
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AI
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Performance of actors，lines
Setting of stage，reality on the story
Reality of manga (comics)
Reality of novels
Springhead:An open source physics simulator [email protected]
Levels of Reality
Mind
Recognition
Action/Behavior
Sensors
Interface
Computer
Presentation
Input
Measurement
Virtual world
Motor control
Reality of surface
Level of sensation and interface
Reality of content
Level of cognition and model
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Springhead:An open source physics simulator [email protected]
Perfect simulation
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Is perfect simulation of the real world possible ?
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Springhead:An open source physics simulator [email protected]
Perfect simulation
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Is perfect simulation of the real world possible ?
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No
Perfect simulation of the real world is impossible.
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Simulation of an atom requires some bytes of memories.
 Numbers of bytes of memory for real simulation of the real world are larger
than number of atom in the real world.
 One bit of memory consists of a lot of atoms.
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The scale of quark to universe is 1040
powers of 10
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We must pick up essence of the world.
But, what is essence?
It depends on the purpose of the virtual reality system.
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Springhead:An open source physics simulator [email protected]
Purpose of virtual world system
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Many applications
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Communication, telepresence, teleconference, teleoperation
Education, training, computer aided engineerings
Evaluation of design
Media for art / entertainments.
Examples of essences of the real world
Evaluation on
vistas of urban
designs
Important
- Color of sky
Negligible
- People in
the city
Training for peace keeping forces
Important
-People in
the city
- cars
Negligible
- Color of sky
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Springhead:An open source physics simulator [email protected]
Reality of virtual world
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Reality of virtual object
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Measurement and modeling
Motion and reaction
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Physics simulation
Reality of characters
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Motion of creatures
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Simulation of creatures
Authoring of artist
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Springhead:An open source physics simulator [email protected]
Summary
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The reason why virtual reality is possible
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Window of sensation
Reproduce essence of the real world
Realities on contents of virtual reality are important.
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Simulation techniques realize
reality of motions and reactions.
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Springhead:An open source physics simulator
Reality of virtual object
Physics simulation for Virtual world
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Springhead:An open source physics simulator [email protected]
Example of physics simulation for VR
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They often called “Physics Engine”
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Springhead:An open source physics simulator [email protected]
What is physics engine ?
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Usual modeling of dynamics and simulation
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Manual formulation
(ml  I )  mg sin 
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
Find this equation with
mysterious algorithm in human brain.
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Lagrangian also requires
(ml  I ) 2  mg cos 
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some human intelligence
to find formulation of energy
  L  L


 (ml  I )  mg sin   0
 
t    
L  K U 
 ODE
Solver
Springhead:An open source physics simulator [email protected]
What is physics engine ?
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Physics engine
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Forward dynamics is automatically computed from the
configuration of the scene with formal algorithm.
fc

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mv  f c  mg
  rc  f c
Iω
Other than constraint force fc ,
Newton and Euler’s equation requires external
force and it’s application point only.
So, physics engine calculate constraint force fc with formal
algorithm.
⇒ Human intelligence is no longer required.
Springhead:An open source physics simulator [email protected]
Finding the constraint forces

Algorithm for constraint force computation
Multi body rigid body dynamics simulators
Impluse
method
Analytic method
Penalty method
Full DOF method
Hahn 88
Mirtich 96
Sequential Projection LCP and iterative solver
of relative
collision
velocity on
Acceleration Velocity based
(J. J. Moreau Contact
based
Stewart 96
’s) method surface
bullet
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Harmon
08
ODE
Baraff 89
Reduced DOF
method
Springhead1
Armstrong 79
Featherstone 83
OpenTissue Springhead2
Most VR and games employ Physics Engines of
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Velocity based constraint representation
LCP based formulation
with Iterative solver
(Springhead and Sprighead2 are physics engines we developed)
Moore &
Williams 89
Springhead:An open source physics simulator [email protected]
Constraint force calculation
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Penalty method
mv  f c  mg
  rc  f c
Iω
e
fc  (ke  be )
ODE solver
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LCP based method

mv  f c  mg
  rc  f c
Iω
To find constraint force fc,
solve these simultaneous equations.
ω  rc  v  0
Description of constraint by the velocity
of the constraint point.
rc

v, w
I,m
Springhead:An open source physics simulator [email protected]
Constraint force calculation
mv  f c  mg
  rc  f c
Iω
 m  v   1 
 mg 
fc   

   
I  ω   rc  

 0 
M
ω  rc  v  0


v
v c  1  rc    0
J
ω

Constraint
u
Jt
fe
Mu  J t fc  fe
u  M 1J t f c  M 1f e
u[t  1]  M 1J t f c h  M 1f e h  u[t ]
v c [t  1]  Ju[t  1]
 JM 1J t f c h  JM 1f e h  Ju[t ]
Af c  b  0
fc   A 1b

v c  Af c  b
Equation of motion
Other than modeling of constraint, the algorithm is completely
formal and no human intelligence is required.
Springhead:An open source physics simulator [email protected]
General case
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Case of two objects
mj I j
vj wj
mass M
velocity
u
Constraint
force
fc
External
force
fe
rj
ri
mi I i
vi wi
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Case of many objects
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Springhead:An open source physics simulator [email protected]
Constraint of Hinge joint
Relative velocity and angular velocity on the joint
w
l
j
Constraint force and torque on the joint
e1
i
w 4, l4
e2
w 6 , l6
e3
w 1, l1
w5 , l5w2,, l2
w 3, l3
Velocity
Coordinate system for constraints
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Axis e3 is free. ⇒ No torque
Other axes are fixed ⇒ No velocity
Force
Velocity
Force
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Springhead:An open source physics simulator [email protected]
Integration of constraints
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Variable transformation of equation of motion

Integrate constraint into the equation of motion
Constraint (hinge’s case)：
Substitute constraint for the equation of motion
Now we got the constraint forces.
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Springhead:An open source physics simulator [email protected]
Whole process of the simulation
1.
Find the constraint force
Springhead employs Gauss-Seidel iterative solver to solve this equation for l.
2.
Update velocities of objects
3.
Update positions of objects
Position
Position and
Orientation
of objects
Orientation
Quaternion
A matrix translating
velocity into diff of
quaternion
Springhead:An open source physics simulator [email protected]
Constraint and LCP
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Many kind of constraints can be modeled by Linear
Complementary conditions.
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Joints
Contacts
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Normal forces and friction forces
Springs and dampers
:
:
Finding of constraint forces to satisfy these conditions
and equations of motion
results in Linear Complementary Problem (LCP).
Springhead:An open source physics simulator [email protected]
Contact point
Relative velocity between the contact
Contact force
velocity
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No interferences
＝stopping by contact force or leaving without force：
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Static or dynamic friction：
force
velocity
force
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No torques：
velocity
force
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Springhead:An open source physics simulator [email protected]
Contact point
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Equation of motion
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Constarint
velocity
force
velocity
force
There looks two variables (l and w).
However, one of two variables is fixed
because of linear complementarily.
So, this equation has a explicit solution.
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Springhead:An open source physics simulator [email protected]
Joint and contact
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We modeled contact and joint.
So, objects with joints and contacts can be simulated.