Computer Graphics for Virtual  
and Augmented Reality  
Lecture 02 Introduction to  
Virtual Reality  
Edirlei Soares de Lima  
What is Virtual Reality?  
From Reality to Virtual Reality:  
Mixed Reality  
Reality (AR)  
Reality (VR)  
In virtual reality, users are immersed in a  
computer-generated environment.  
Virtual Reality  
Main characteristics:  
Immersion: user feels immersed in the computer-generated  
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  
Goal of VR: create a high degree of presence  
Make users believe they are in the virtual environment.  
Produced by:  
Quality of graphics/sound  
Enveloping environment  
Natural interaction  
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 (  
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)  
Head-Mounted Display (HMD)  
Key Properties of HMDs  
Focal length, Field of View  
Occularity, Interpupillary distance  
Resolution, Contrast  
Power consumption, brightness  
Refresh rate  
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  
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  
Cameras + image processing algorithms  
Armature with joints + angle measurements  
Gyroscopes + accelerometers  
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  
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  
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  
Performance Criteria for Tracking Methods  
Jitter: changes in tracker output when stationary (sensor  
Performance Criteria for Tracking Methods  
Drift: steady increase in tracker error over time (accumulative  
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.  
Further Reading  
Sherman, W. R., Craigm A. B. (2003). Understanding Virtual Reality:  
Interface, Application, and Design (1st ed.). Morgan Kaufmann. ISBN: 978-  
Chapter 1: Introduction to Virtual Reality  
Chapter 2: VR The Medium  
Chapter 3: Interface to the Virtual World Input  
Chapter 4: Interface to the Virtual World Output