Introduction to Simulation and VR Week 5 Human Dynamics in a Virtual World
Jan 05, 2016
Introduction to Simulation and VR
Week 5
Human Dynamics in a Virtual World
Recap
Calculate Geometry
Draw Wire Frame
Render Surfaces
Enhance Surfaces and lighting
Sensor input and output
Initialize world
Human Dynamics Users described as participants basic interaction involves control of camera
(viewpoint) exploratory navigation / locomotion Walk-through or Fly-Thru (sic!)systems
More advanced environment allow interaction Touch , selection, manipulation referred to as direct manipulation
Components of interaction
VR model Simulation of body Interaction with virtual body Object pair collision General collision detection
VR Model
Goal of Being There Presence or Telepresnce Held and Durlach 1992, Draper 1998
Must model expectations -> realism Ideal VR model must Immerse participant in
visual, audio, touch , smell and taste Humans can process several audio streams
and can focus and segrgate on one - Wenzel 1992
VR model - Immersion Surrounds body fills visual field extensive inclusive (replaces reality) Vivid human body
in CAVE actual body can obscure projection of virtual objects
In HMD body must be represented
VR model - HCI Mouse and keyboard has two problems
gulf of execution gulf of evaluation
Hutchins 1986
Direct Manipulation paradigm Tracked HMD is simplest form 0- 1 to 1
mapping, Low cognitive overhead Using mouse - must map actions to different
translations
VR Model - Interaction Immersion and tracking rely on registration Registration implies that motion of limbs
accurate Better appreciation of 3D environment Cannot lose interaction - reduces gulf of
execution Gulf of evaluation reduced when whole virtual
body used - Slater and Usoh 1994, Mine 1997
Simulation of Body
Body model is the description of the interface eyes are visual interface, ears are audio interface geometric description drawn from egocentric point of
view description of hand and fingers forms basis of
grasping simulation for picking up objects (Boulic 1996)
Simulation of Body- Building the body The more points representing the body the more
realistic the movement Up to 90 points for motion-capture in animation Standard for human skeleton (H-Anim 1999) More typically head, Torso, Both hands Inferred movement from limited points Inverse kinematics problem - infinite possibilities of
movement in virtual environment, consistent restraint
Elbow position in 4- Tracker system (Badler, 1993)
H-Anim
Humanoid
Sacroiliac
L MidtarsalL AnkleL KneeL Hip
R MidtarsalR AnkleR KneeR Hip
L WristL ElbowL Shoulder
R WristR ElbowR Shoulder
vl5
Skullbase
Different sensing methods
Simulation Of body - tracking the participant Choice of system depends on 5 factors
accuracy, resolution, range, lag, update rate Many different tracking technologies
Meyer 1992 frequency and time
ultrasonic time-of-flight measurement Pulsed Infra-red GPS Optical Gyroscopes Phase difference
Simulation Of body - tracking the participant
Spatial Scan Outside-in Inside-out
Inertial sensing mechanical gyroscope Accelerometer
Mechanical Linkages Direct - Field Sensing
Head tracking
Head tracking
Accelerometer
Fast Track
Phantom
How the tracker works
Distance detection
Transmitter
Receiver
How the tracker works
Orientation detection
Transmitter
Receiver
Head tracking
Head tracking
Latency Filtering, keep steady Jitter
Mechanical Linkages
Sensors in joints detect position 3D viewer updates Robot applies force to joints Force is felt on hand
Phantom
Phantom working
θ1
θ2
θ3
Virtual pencil
Phantom working
θ1
θ2
θ3
Virtual pencil
Phantom working
θ1
θ2
θ3
Virtual pencil
Phantom working
θ1
θ2
θ3
Virtual pencil
Apply force
Phantom working
θ1
θ2
θ3
Virtual pencil
Apply force
Motors lock
Phantom working
θ1
θ2
θ3
Virtual pencil
Interaction with virtual Body
Limitations mean reliance on metaphors for object manipulation (grasping and moving) locomotion (movement)
Limitations in haptics mean that restraint on the virtual environment exists
Object Manuipulation
World
Body B Object O
Hand H Object P
World
Body B Object O
Hand H
Object P
Grasping
Releasing
Object Manipulation
Hand posture may not be tracked - makes grasping difficult
Must establish a point at which union is deemed to have taken place
Moved by repositioning in the scene graph Robinett and Holloway 1992
Locomotion
Tracker has a limited range Must use locomotion metaphor to move
greater distances Locomotion is on an even plane , virtual
terrain may not be Collision detection can be employed to raise
or lower the participant accordingly
Transformations employed in object manipulation
Calculate relative transformation from hand to object MR
MR = (MB.MH)-1.MO.MP
MB :Transformation from body to world co-ords
MH :Transformation from hand to body co-ords
MO :Transformation from Object O to world co-ords
MP :Transformation from Object P to Object O co-ords
After manipulation new local transformation of Object Mp’ is
Mp’ = MO-1.MB.MH .MR
Locomotion
Tracker has a limited range Must use locomotion metaphor to move
greater distances Locomotion is on an even plane , virtual
terrain may not be even Collision detection can be employed to raise
or lower the participant accordingly
Fly in direction of aimFly in direction of pointingFly in direction of gazeFly in direction of torso
Directions of locomotion
Object Pair Collision Detection
Vital component of interaction Describe Exhaustive Test for when two object
intersect (process hungry) Try to aviod doing exhaustive test igf possible
Exhaustive Test
Assume all objects as collection of triangles (polygons)
Object 1 consists of m triangles Object 2 consists of n triangles Use triangle intersection test to test all
possible pairs of of intersections This requires n.m triangle-triangle tests
Triangle Intersection Test
Moller 1997 comparison of triangles A and B
They do not intersect if all vertices in A lie to one side of plane of B and V.V
Otherwise plane of A intersects plane of B on L
Find line intersection of L with A (LA) and L with B (LB)
A and B intersect only if LA and LB overlap
AB
LB
L LA
Basic Rejection Tests Simplest tests based on distance Each scene object has a bounding sphere. Two
objects cannot overlap if distance between two centres is > than sum of the radii
Better test id the separating plane test. If a plane can be drawn such that all points of one object lie on one side and all points of the other on the reverse, cannot collide. Key ids to find a good separating plane
Bounding Box range test
General Collision Detection
Detecting collision between a set of n objects generates n2 possible pairs of objects requiring testing for overlap
Use spatial partitionong to discard as may pairs as possible and use object pair collision tests on remaining pairs
Uniform Space Subdivision
Space Subdivision
Recap
Immersion requires body representation Track body Robot arm - inverse kinematics Monitor collisions Force Feedback Uses inverse kinematics Scene manipulation