Development Of Simulation and VR

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 participantsbasic interaction involves control of

camera (viewpoint) exploratory navigation / locomotion Walk through systems

More advanced environment allow interaction Touch , selection, manipulation referred to as direct manipulation

Components of interaction

VR modelSimulation of bodyInteraction with virtual bodyObject pair collisionGeneral collision detection

VR Model

Goal of Being There Presence or Telepresnce Held and Durlach 1992, Draper 1998

Must model expectations -> realismIdeal 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 - ImmersionSurrounds bodyfills visual fieldextensive inclusive (replaces reality)Vividhuman 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 paradigmTracked HMD is simplest form 0- 1 to

1 mapping, Low cognitive overheadUsing mouse - must map actions to

different translations

VR Model - InteractionImmersion and tracking rely on

registrationRegistration implies that motion of limbs

accurateBetter appreciation of 3D environmentCannot lose interaction - reduces gulf of

executionGulf 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 viual 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 bodyThe more points represneting the body the

more realistic the movementUp to 90 points for motion-capture in animationStandard 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

Simulation Of body - tracking the participantChoice 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 measurementPulsed Infra-redGPSOptical GyroscopesPhase difference

Simulation Of body - tracking the participant

Spatial ScanOutside-inInside-out

Inertial sensing mechanical gyroscope Accelerometer

Mechanical LinkagesDirect - Field Sensing

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

Virtual Bodies

VBs are represenetations of human involvement in 3D applications and VR

Hierarchical connected geomtry specifications

Principles similar to robotics

What is a robot?

Joseph Engelberger, a pioneer in industrial robotics, once remarked "I can't define a robot, but I know one when I see one."

Many different machines called robots Everybody has a different idea of what constitutes

a robotName from robota – forced labour

What relevance to us?

VR models use robotic principlesAvatars behave like robotsSimulations of robots used to test

real robotsMay be used to control remote

robotics

Robot Arm

Fitted with end effectorUsually interchangeableArtificial Hand , paint gun, welding rodPressure sensor needed to prevent

crushingProgrammed by incremental steps

which are then replicated ad infinitum

Frameworks, Chains (or Skeletons)

A lot of mechanical objects in the real world consist of solid sections connected by joints

Obviously robot arm but also Creatures such as humans and animals. Car Suspension Ropes, string and Chains

Frameworks, Chains (or Skeletons)

Sections and joints of robot arm are known as a 'chain‘

In creatures could be referred to as a skeleton

Moveable sections correspond to bones

Attachments between bones are joints.

Frameworks, Chains (or Skeletons)

Motions of chains can be specified in terms of translations and rotations.

Forward Kinematics - From the amounts of rotation and bending of each joint in an arm, for example, the position of the hand can be calculated.

Inverse Kinematics - If the hand is moved, the rotation and bending of the arm is calculated, in accordance with the length and joint properties of each section of the arm.

Joint Translation-Rotation

We can use a transform (T) to transform each point relative to the body to a position in world coordinates.

If we want to model both linear and angular (rotational) motion then we need to use a 4x4 matrix to represent the transform

What is Inverse Kinematics?

Forward Kinematics

Base

End Effector

?

What is Inverse Kinematics?

Inverse Kinematics

Base

End Effector

What does looks like?

?

Base

End Effector

Solution to

Our example

Number of equation : 2

Unknown variables : 3

Infinite number of solutions !

Redundancy

System DOF > End Effector DOF

Our example

System DOF = 3End Effector DOF = 2

Redundancy

A redundant system has infinite number of solutions

Human skeleton has 70 DOF Ultra-super redundant

How to solve highly redundant system?

Iterative solution

Start at end effector Move each joint so that end

gets closer to target The angle of rotation for each

joint is found by taking the dot product of the vectors from the joint to the current point and from the joint to the desired end point. Then taking the arcsin of this dot product.

To find the sign of this angle (ie which direction to turn), take the cross product of these vectors and checking the sign of the Z element of the vector.

Goal Potential Function

“Distance” from the end effector to the goal

Function of joint angles : G()

Our Example

Base

End Effector

Goal

distance

Limitations

Will G() be always zero? No : Unreachable Workspace

Will the solution be always found? No : Local Minima/Singular

ConfigurationWill the solution be always unique?

No : Redundancy

Applications to VR/3d Apps

Control of humanoid componentsCan be considered complex chains of

interconnected geometrical objectsActivities

Grasp Walk Collide Interact with other objects

Object Manipulation

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 rangeMust use locomotion metaphor to

move greater distancesLocomotion is on an even plane ,

virtual terrain may not beCollision detection can be employed

to raise or lower the participant accordingly

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 rangeMust use locomotion metaphor to

move greater distancesLocomotion is on an even plane ,

virtual terrain may not beCollision 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

Books and Articles:

The Handbook of Virtual Environments (2002), Kay Stanney (ed), Lawrence Erlbaum.

Isdale, J., 1998, What is VR? http://www.isdale.com/jerry/VR/WhatIsVR.html

Kalawsky, R., 1993, The Science of Virtual Reality and Virtual Environments, Addison Wesley.

Rheingold, H., 1991, Virtual Reality, Secker and Warburg, London.

Wilson, J.R., D’Cruz, M., Cobb, S. and Eastgate, R., 1996, Virtual Reality for Industrial Applications, Nottingham University Press.

Resources

www.vrweb.com (VR Solutions Company)www.barco.com/projection_systems/

virtual_and_augmented_reality/www.sgi.com (VR Solutions Company)www.ptc.com (free modelling program)www.sense8.com (trial VR program)www.crystalspace.com (free Games

Engine)