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