Computer
Graphics
|
Lecture
2 - Computer Hardware and Software
|
Video Display Devices
Cathode Ray
Tube (CRT)

Vector Display
Random Scan
display
Calligraphic
Refresh Display
Direct-view
Storage Tube Display

Raster Display


CLUT

Flat Panel
Displays
Emissive:
Plasma
Each pixel
made of three cells containing xenon and neon gas
Horizontal and
vertical electrodes create unique grid to locate cell positions
Gas in
each cell is ionized when a voltage difference is applied to intersecting
electrodes
The
current creates a rapid flow of charged particles, which stimulates the gas
atoms to release photons of ultraviolet light
Photons excite
the phosphor coated on the inside wall of the cell.


(Pictures from: "How
Plasma Displays Work")
Non-emissive:
LCDs\
Organic
molecules that align themselves in crystalline structures in the absence of
external forces
Application of
external force rearranges them as if they were a liquid
Liquid
crystals respond to heat or electromagnetic forces
LCDs used as
optical modulators
Change
polarization
In unexcited
or crystalline state, LCDs rotate the polarization of light by 90 degrees.
In the
presence of an electric field, LCDs behave like a liquid and align their
electrostatic charges with E field.



Augmented Display Systems
Virtual Reality
Definition - VR is a computer generated, interactive,
three-dimensional environment in which a person is immersed.
- This
implies:
- Requires a high performance computer graphics
system to provide an adequate level of realism.
- The virtual world is interactive. A user requires real-time
response from the system to be able to interact with it in an effective
manner.
- The last point is that the user is immersed in this
virtual environment. This usually means that the user wears a head
mounted display.
Virtual Reality Interface Devices
HMD - head mounted
display
- Best
known approach to VR
- Coupled
with head tracking
- Stereo
binocular view of the virtual world often with stereo audio
- By
virtue of tracking the viewing position (the head) and orientation in the physical
world, the view and perspective of the virtual are consistent with what
one would experience in the physical world from the same actions.
- Permit
some means of input, such as a dataglove or some other high degree of
freedom input to support interaction with the displayed virtual
world.
- stereo
display, much like a pair of glasses that provides a view into the virtual
world.
- The
physical form of these “glasses” can range from something on the scale of
a motorcycle helmet to a pair of sunglasses
- Great
variety in display quality
- Goal
is to provide the widest field of view at the highest quality and with the
least weight and at a reasonable cost.
- Issues:
- HMDs cover eyes
- Virtual world seen at the expense of the physical.
- Users cannot directly see:
- their hands or the devices that they are
controlling
- objects or other people who are in their immediate
physical environment
- Solution:
- Some representation of physical world entities
must appear in the virtual
- Mount one or more video cameras onto the HMD and
feed the signals to the displays

Surround Environments
Cave based VR
- User
functions within a room on which one or more of the surfaces (walls, floor,
ceiling …) is the display
- Some
or all of the walls of a room are rear-projection stereo displays
- User
wears glasses to enable viewing of stereo images
- Since
glasses are transparent, one can see the physical as well as the virtual
world
- Computer
generated objects appear to enter into the physical space of the Cave
itself, where the user can interact with them directly
- User’s
head position is tracked within the Cave so that what is displayed
preserves proper perspective, etc., in adapting to movements and change of
location of gaze
- Issue:
- Two people in cave - both are viewing the same
displays, preventing each from own “point of view.”
- Both viewers look at different things and
different directions, but do so as if from the perspective of the current
location of the head tracker.
- Some
mechanism for interacting with what is scene.
1992/93 - EVL's
Cave (http://www.evl.uic.edu/home.html
)
Cruz-Neira, Sandin, DeFanti, Kenyon and Hart
Electronic Visualization Lab - University of Illinois at Chicago Circle
- Generic
Immersive VR Environment
- A
theater 10x10x9 feet, made up of three rear-projected screens for walls
and a reflective projection for the floor.
- High
resolution, high bandwidth, short persistance CRT projectors throw
full-color workstation fields (1024x768 stereo) onto the screens, giving
approximately 3,000 linear pixel resolution to the surrounding composite
image.
- Computer-controlled
audio provides a sonification capability to multiple speakers.
- User's
head and hand orientation and position are aquired using an Ascension
tracking system with tethered electromagnetic sensors.
- Stereographics'
LCD stereo shutter glasses are used to separate the alternate fields going
to the eyes.
- SGI
InfiniteReality Engine is used to create the imagery that is projected
onto the walls and floor.


VEMovie.mov


Trimension
Cabin - Fully enclosed cave
Image Construction : 5 - 6 Cameras

Domes and Walls
SkyVision Full-Dome
(SkySkan.com)
- Sloping
seats, zenith position.
- Different
projector orientations .

Imax
- Primary
goal is to fill peripheral vision.
- 16:9
aspect ratio format

Personal Domes


Elumens Visionstation (VS) - Hemispherical Display
Elumens Visionstation (VS3)
Elumens Visionstation (VS3)
Depth: 8'-10" (106")
Height: 7'-9" (93")
Width: 11'-4" (136")
Partial Immersion
Panoramic - Curved Walls
- Typically
use RGB projectors (Varing focal depth)
- Edge
blending (On computer or with video hardware)
- Small
"sweet" spot.


Trimension (others - Barco)
MultiWalls
- How to synchronise multiple devices (Computer, DVD)
- Multiple pipe graphics cards (Cost)
- Seams between walls (Aligned, edge blending)
- Front vs back projection (Space)


Three Wall - CAEV - Melbourne
University
Two Wall - PortaWedge - Melbourne
U.
Tables, Desks, Single Screens
Immersadesk 2 - EVL
Fakespace
Trimension

The Grip Project - UNC Chapel Hill - Molecular Visualization
The NanoManipulator - UNC Chapel
Hill
http://www.cs.unc.edu/Research/nano/
Movie
Responsive Workbench - 1993
- 3D
interactive workspace originally developed by Wolfgang Krueger at GMD
- Computer-generated
stereoscopic images are projected onto a horizontal tabletop display
surface via a projector-and-mirrors system, and viewed through shutter
glasses to generate the 3D effect
- A
6DOF tracking system tracks the user's head, so that the user sees the
virtual environment from the correct point of view.
- A
pair of gloves and a stylus, also tracked by the system, can be used to
interact with objects in the tabletop environment.


Low Cost Stereo Table - Pace University (CAM)

Cubby - Delft


Stereoscopic Displays


Mount Fuji Stereo Pairs
Free Viewing
Cross Eyed Viewing
Left Eye
Right eye
Left Eye

5DT HMD 800
Display Resolution: 800x600x3(rgb)
pixels - Full SVGA
Optics Field of View: 28 (H)
x 21 (V) degrees
Headphones:
Type: Sennheiser HD 25 closed
dynamic headphones
Frequency Responce: 16Hz -
22Hz (3dB)
- Shutter
Glasses (Active Stereo)


Crystal Eyes (Stereographics )

- Polarized
Glasses (Passive Stereo)
Autostereographic Display



Dresden 3D (also Stereographics
and others) - 15" - 18"


MultiMo3D , Heinrich-Hertz-Institut für Nachrichtentechnik, Germany
Principles and prototype of a 50-inch projection-type dual lenticular screen
3D display.
Volumetric Display -
Actuality Systems
Image Size
and Display Type
- Approx.
10" diameter spherical image
- Swept-screen multiplanar volumetric display
- Autostereoscopic: no viewing goggles
- Volume-filling imagery
- Supports many simultaneous viewers – no
head-tracking

Input Hardware
Tracker - Head
position and Orientation
- Determines viewpoint of
virtual world
- 5DT
3D-BIRD
- tracking of orientation angles
- move up, down, side to side, and rotate
(yaw, pitch and roll)


Datagloves - Hand position and orientation
- Monitors
status of user's fingers
- 5DT
Data Glove 5 (www.5dt.com )
Measures each finger flexure and the
orientation (pitch and roll) of the user's hand

Haptics - Force Feedback

Other Input/Output Devices
Image Scanners
Printers
(Raster)
Laser
Inkjet
Plotters
(Vector)

3D Printing
Stereolithography
(from howstuffworks.com
)
Create a 3-D
model of object
Software slices
model into thin layers -- typically five to 10 layers/millimeter
The 3-D
printer's laser "paints" one of the layers, exposing the liquid
plastic in the tank and hardening it
The platform
drops down into the tank a fraction of a millimeter and the laser paints the
next layer
This process
repeats, layer by layer, until your model is complete

Mpeg Movie of part
Ink-jet
Printing – (e.g. Z-Corp )
- The
3D Printer spreads a thin layer of powder
- An ink-jet
print head prints a binder in the cross-section of the part being created
- The
build piston drops down, making room for the next layer, and the process
is repeated
- Whenthe
part is finished, it is surrounded and supported by loose powder, which
is then shaken loose from the finished part.

Graphics Software
Languages ->
Commands -> APIs
Coordinate
Systems
Local
Coordinates
World
Coordinates
Device
Coordinates
Transformations
Model
-> World -> Normalized -> Device
Graphics
Functions
General
purpose graphics packages provide:
Functions
– I/O, attributes, transformations, viewing
Output
primitives – building blocks of images
Attributes
– properties of images
Geometric
transforms
Viewing
transforms
Software
Standards:
GKS
Phigs
OpenGL – http://www.opengl.org/
Web3D – www.web3d.org