Introduction to Virtual Reality

Computer Graphics for Virtual

and Augmented Reality

Lecture 02 – Introduction to

Virtual Reality

Edirlei Soares de Lima

<edirlei.lima@universidadeeuropeia.pt>

What is Virtual Reality?

•

From Reality to Virtual Reality:

Mixed Reality

Real

World

Augmented

Reality (AR)

Virtual

Reality (VR)

Virtual

World

–

In virtual reality, users are immersed in a

computer-generated environment.

Virtual Reality

•

Main characteristics:

–

Immersion: user feels immersed in the computer-generated

environment

•

Immersion and presence: while immersion describes the extent to which

technology can deliver a vivid illusion of reality, presence represents the state of

consciousness and sense of being in the virtual environment

–

Interaction: user can interact with virtual content

Independence: user can have an independent view and react to the

environment

•

Goal of VR: create a high degree of presence

–

Make users believe they are in the virtual environment.

Immersion

•

Produced by:

–

Quality of graphics/sound

Enveloping environment

Natural interaction

Realism

Presence

•

Presence is the subjective experience of being in one place or

environment even when physically situated in another.

–

Mental immersion – suspension of disbelief

–

Physical immersion – bodily entering the medium

Reality vs. Virtual Reality

Creating the Illusion of Reality

•

Fooling human perception by using technology to generate

artificial sensations.

Example: Birdly (https://www.youtube.com/watch?v=gHE6H62GHoM)

–

Create illusion of flying like a bird

–

Multisensory VR experience (visual, audio, wind, haptic)

Technologies for VR Systems

•

Display (Immersion)

–

Simulates senses (visual, auditory, tactile)

Tracking (Independence)

–

Allow users to change viewpoint

–

Independent movement

•

Input Devices (Interaction)

–

Supports user interaction

Using Technology to Stimulate Senses

Head-Mounted Display (HMD)

Key Properties of HMDs

•

Lens

–

Focal length, Field of View

–

Occularity, Interpupillary distance

Display

–

Resolution, Contrast

Power consumption, brightness

Refresh rate

•

Ergonomics

–

Size, Weight, Wearability

Focal Distance

•

The lenses make possible to focus on the images produced by

the display that is very close to a user’s eyes.

–

The lenses are placed between the screens and the viewer’s eyes,

giving the illusion that the images are out to a distance where they can

be viewed comfortably.

focus distance

virtual image

screen

eye

optics

Distortion in Lens Optics

•

To Correct distortions:

–

Must pre-distort the image

–

Pixel-based distortion using shader programming

Distortion in Lens Optics

Field of View

•

Monocular FOV:

–

The angular size of the displayed image as

measured from the pupil of one eye.

Total FOV/Stereoscopic FOV:

–

total angular size of the displayed image visible

to both eyes.

•

FOV may be measured horizontally,

vertically or diagonally.

Oculus Rift

•

FOV: 110º Horizontal

Refresh rate: 90 Hz

Resolution: 1080x1200/eye

3-DOF orientation tracking

3-axis positional tracking

Comparison Between HMDs

Computer Based vs. Mobile VR Displays

Projection/Large Display Technologies

•

CAVE Systems:

Projection/Large Display Technologies

•

CAVE Systems:

Vehicle Simulators

•

Combine VR displays with vehicles

–

Visual displays on windows

Motion base for haptic feedback

Audio feedback

•

Physical vehicle controls

– Steering wheel, flight stick, etc

Full vehicle simulation

–

Emergencies, normal operation, etc

Weapon operation

Training scenarios

Tracking Technology

•

For immersion, when the user changes position in the real

world, the VR view also needs to change.

–

Requires tracking of the user’s pose (position and orientation) in the

real world.

Tracking in VR

•

Common tracking elements:

–

Head position and orientation

Body position and orientation

Hands position and orientation

Fingers, legs, torso, eyes, etc.

Degrees of Freedom:

Main Tracking Methods

•

Camera-based:

–

Cameras + image processing algorithms

Mechanical:

–

Armature with joints + angle measurements

Inertial:

–

Gyroscopes + accelerometers

•

Electromagnetic:

–

Magnetic field generators + magnetic field detectors

Camera-Based Tracking Methods

•

Fast and high-resolution cameras

–

Number of cameras depends can affect the precision

•

Typically, two or more for VR

–

Normal camera or infrared cameras

Camera-Based Tracking Methods

•

Projective Geometry Techniques

–

Single camera vs. multiple cameras

Camera-Based Tracking Methods

•

Point Tracking Techniques:

–

Infrared light and infrared cameras

Reflector balls

Single or multiple cameras

Camera-Based Tracking Methods

•

Sphere Tracking Techniques:

–

2D position translates to line in 3D

–

Sphere size translates to distance

Camera-Based Tracking Methods

•

Outside-in Tracking

–

Stationary cameras and moving

markers

Inside-out tracking

–

Camera on/in the device

Performance Criteria for Tracking Methods

•

Static Accuracy:

–

Ability of the tracking method to determine the coordinates of a

position in space when the sensors and tracked objects are not

moving.

–

Depends on sensor sensibility, algorithms, and environment.

•

Dynamic Accuracy:

–

Ability of the tracking method to determine the coordinates of a

position in space as the sensors and tracked objects move.

–

Depends on static accuracy, movement, and occlusions.

Performance Criteria for Tracking Methods

•

Accuracy: difference between actual position and measured

position

Performance Criteria for Tracking Methods

•

Jitter: changes in tracker output when stationary (sensor

noise)

Performance Criteria for Tracking Methods

•

Drift: steady increase in tracker error over time (accumulative

error)

–

Can be controlled by periodic recalibrations.

Performance Criteria for Tracking Methods

•

Latency: time between a change in the object position and

the time the sensors detect the change.

–

Large latency (> 10 ms) can cause simulation sickness.

–

Larger latency (> 50 ms) can break VR immersion.