Advanced Computer Graphics - WordPress.com

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Nov 8, 2013 (3 years and 7 months ago)

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Index

Contents

1.
Introduction



Definition



Meaning



Historical Prospective



Objective, scope and limitations

2.
Literature



What



How

3. Research Design



Hypothesis

4. Research



How



Input and Output

5. Data Analysis

6. Synthesis



Introduction



General Observation
& Specification

7. Conclusion



Finding Implementation










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Initial Development of Computer Graphics

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Image types

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2D computer graphics

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3D compu
ter graphics

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Computer animation

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11

Concepts and principles

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Rendering

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12

Volume rendering

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15

3D modelling

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15

Subfields in computer graphics

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Geometry

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18

Animation

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Rendering

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Geometry processing

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Cloth modelling

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Deformable solids

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Mass
-
spring models

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23

Finite ele
ment simulation

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Energy minimization methods

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25

Shape matching

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25

Rigid
-
body based deformation

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.

25

Force
-
based cloth

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26

Position
-
b
ased dynamics

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Collision detection for deformable objects

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Rigid body dynamics

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Rigid body linear momentum

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Rigid body angular momentum

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Angular momentum and torque

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Applications

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AutoCAD origin

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AutoCAD LT

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AutoCAD Freestyle

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Student ve
rsions

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Vertical programs

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AutoCAD Architecture

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Autodesk Maya

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Awards

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Overview

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Maya Embedded Language
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System requirements

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Operating systems
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Autodesk Revit

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Modelling

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Intended use
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Family based content

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Rendering

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Autodesk 3ds Max

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Modelling techniques

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Polygon modelling

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NURBS or non
-
uniform rational B
-
spline

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Surface tool/Editable patch object

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Predefined primitives

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Predefined Standard Primitives list

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Predefined Extended Primitives list

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Rendering

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Definition

The development of

computer graphics

has made computers easier to interact
with, and better for understanding and interpreting many types of data.
Developments in computer
graphics have had a profound impact on many types of
media and have revolutionized

animation,

movies

and the

video game

industry.
The
term computer graphics has been used in a broad sense to describe "almost
everything on computers that is not text or soun
d". Typically, the term

computer
graphics

refers to several different things:



the

representation

and

manipulation

of

image

data

by a

computer



the various

technologies

used to create and manipulate images



the

images

so produced, and



the sub
-
field of

computer science

which studies methods for digitally synthesizing
and manipulating visual content, see

study of computer graphics


Meaning

Today, computers and computer
-
generated images touch many aspects of daily life.
Computer imagery
is found on television, in newspapers, for example in weather
reports, or for example in all kinds of medical investigation and surgical procedures.
A well
-
constructed

graph

can present complex statistics in a form that is easier to
understand and interpre
t. In the media "such graphs are used to illustrate papers,
reports, thesis", and other presentation material
.

Many powerful tools have been developed to visualize data. Computer generated
imagery can be categorized into several different types: 2D, 3D,
4D, 7D, and
animated graphics. As technology has improved, 3D computer graphics have
become more common, but 2D computer graphics are still widely used. Computer
graphics has emerged as a sub
-
field of

computer science

which studies methods for
digitally synthesizing and manipulating visual content. Over the past decade, other
specialized fields have been developed like

informa
tion visualization
, and

scientific
visualization

more concerned with "the visualization of

three dimensional

phenomena
(architectural, meteorological, medical,

biological
, etc.), where the emphasis is on




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realistic renderings of volume
s, surfaces, illumination sources, and so forth, perhaps
with a dynamic (time) component".




Historical Prospective

The advance in computer graphics was to come from Ivan Sutherland. In 1961
Sutherland created another computer drawing program called Sketchp
ad. Using a
light pen, Sketchpad allowed one to draw simple shapes on the computer screen,
save them and even recall them later. The light pen itself had a small photoelectric
cell in its tip. This cell emitted an electronic pulse whenever it was placed in

front of a
computer screen and the screen's electron gun fired directly at it. By simply timing
the electronic pulse with the current location of the electron gun, it was easy to
pinpoint exactly where the pen was on the screen at any given moment. Once t
hat
was determined, the computer could then draw a cursor at that location.

Sutherland seemed to find the perfect solution for many of the graphics problems he
faced. Even today, many standards of computer graphics interfaces got their start
with this earl
y Sketchpad program. One example of this is in drawing constraints. If
one wants to draw a square for example, s/he doesn't have to worry about drawing
four lines perfectly to form the edges of the box. One can simply specify that s/he
wants to draw a box,

and then specify the location and size of the box. The software
will then construct a perfect box, with the right dimensions and at the right location.
Another example is that Sutherland's software modeled objects
-

not just a picture of
objects. In other

words, with a model of a car, one could change the size of the tires
without affecting the rest of the car. It could stretch the body of the car without
deforming the tires.

These early computer graphics were Vector graphics, composed of thin lines
wherea
s modern day graphics are Raster based using pixels. The difference
between vector graphics and raster graphics can be illustrated with a shipwrecked
sailor. He creates an SOS sign in the sand by arranging rocks in the shape of the
letters "SOS." He also h
as some brightly colored rope, with which he makes a
second "SOS" sign by arranging the rope in the shapes of the letters. The rock SOS
sign is similar to raster graphics. Every pixel has to be individually accounted for.
The rope SOS sign is equivalent to

vector graphics. The
computers simply sets the




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starting point and ending point for the line and perhaps bend

it a little between the
two end points. The disadvantages to vector files are that they cannot represent
continuous tone images and they are limit
ed in the number of colors available.
Raster formats on the other hand work well for continuous tone images and can
reproduce as many colors as needed.

Also in 1961 another student at MIT, Steve Russell, created the first video game,
Spacewar. Written for
the DEC PDP
-
1, Spacewar was an instant success and copies
started flowing to other PDP
-
1 owners and eventually even DEC got a copy. The
engineers at DEC used it as a diagnostic program on every new PDP
-
1 before
shipping it. The sales force picked up on thi
s quickly enough and when installing new
units, would run the world's first video game for their new customers.

E. E. Zajac, a scientist at Bell Telephone Laboratory (BTL), created a film called
"Simulation of a two
-
giro gravity attitude control system" in

1963. In this computer
generated film, Zajac showed how the attitude of a satellite could be altered as it
orbits the Earth. He created the animation on an IBM 7090 mainframe computer.
Also at BTL, Ken Knowlton, Frank Sindon and Michael Noll started worki
ng in the
computer graphics field. Sindon created a film called Force, Mass and Motion
illustrating Newton's laws of motion in operation. Around the same time, other
scientists were creating computer graphics to illustrate their research. At Lawrence
Radia
tion Laboratory, Nelson Max created the films, "Flow of a Viscous Fluid" and
"Propagation of Shock Waves in a Solid Form." Boeing Aircraft created a film called
"Vibration of an Aircraft."

It wasn't long before major corporations started taking an interest

in computer
graphics. TRW, Lockheed
-
Georgia, General Electric and Sperry Rand are among
the many companies that were getting started in computer graphics by the mid
1960's. IBM was quick to respond to this interest by releasing the IBM 2250 graphics
termi
nal, the first commercially available graphics computer.

Ralph Baer, a supervising engineer at Sanders Associates, came up with a home
video game in 1966 that was later licensed to Magnavox and called the Odyssey.
While very simplistic, and requiring fairl
y inexpensive electronic parts, it allowed the
player to move points of light around on a screen. It was the first consumer computer
graphics product.





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Also in 1966, Sutherland at MIT invented the first computer controlled head
-
mounted
display (HMD). Called

the Sword of Damocles because of the hardware required for
support, it displayed two separate wireframe images, one for each eye. This allowed
the viewer to see the computer scene in stereoscopic 3D. After receiving his Ph.D.
from MIT, Sutherland became D
irector of Information Processing at ARPA
(Advanced Research Projects Agency), and later became a professor at Harvard.

Dave Evans was director of engineering at Bendix Corporation's computer division
from 1953 to 1962, after which he worked for the next f
ive years as a visiting
professor at Berkeley. There he continued his interest in computers and how they
interfaced with people. In 1968 the University of Utah recruited Evans to form a
computer science program, and computer graphics quickly became his pri
mary
interest. This new department would become the world's primary research center for
computer graphics.

In 1967 Sutherland was recruited by Evans to join the computer science program at
the University of Utah. There he perfected his HMD. Twenty years la
ter, NASA would
re
-
discover his techniques in their virtual reality research. At Utah, Sutherland and
Evans were highly sought after consultants by large companies but they were
frustrated at the lack of graphics hardware available at the time so they star
ted
formulating a plan to start their own company.

A student by the name of

Edwin Catmull

started at the University of Utah in 1970 and
signed up for Sutherland's computer graphics class. Catmull h
ad just come from The
Boeing Company and had been working on his degree in physics. Growing up on
Disney, Catmull loved animation yet quickly discovered that he didn't have the talent
for drawing. Now Catmull (along with many others) saw computers as the n
atural
progression of animation and they wanted to be part of the revolution. The first
animation that Catmull saw was his own. He created an animation of his hand
opening and closing. It became one of his goals to produce a feature length motion
picture u
sing computer graphics. In the same class, Fred Parke created an
animation of his wife's face. Because of Evan's and Sutherland's presence, UU was
gaining quite a reputation as the place to be for computer graphics research so
Catmull went there to learn 3
D animation.

As the UU computer graphics laboratory was attracting people from all over,

John
Warnock

was one of those early pioneers; he would later found Adobe Systems and




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create a revolution in the publishing world with his PostScript page description
l
anguage. Tom Stockham led the image processing group at UU which worked
closely with the computer graphics lab. Jim Clark was also there; he would later
found Silicon Graphics, Inc.

The first major advance in 3D computer graphics was created at UU by these

early
pioneers, the hidden
-
surface algorithm. In order to draw a representation of a 3D
object on the screen, the computer must determine which surfaces are "behind" the
object from the viewer's perspective, and thus should be "hidden" when the
computer c
reates (or renders) the image.




Literature

2D computer graphics

2D computer graphics

are the computer
-
based generation of

digital images

mostly
from two
-
dimensional models, such as

2D geometric models
, text, and di
gital
images, and by techniques specific to them.

2D computer graphics are mainly used in applications that were originally developed
upon traditional

printing

and

drawing

technologies, such as

typography
,
cartography
,

technical
drawing
,

advertising
, etc.. In those applications, the two
-
dimensional

image

is not just a representation of a real
-
world object, but an
independent

artifact with added semantic value; two
-
dimensional models are
therefore preferred, because they give more direct control of the image than

3D
computer graphics
, whose approach is more akin

to

photography

than to

typography
.


Pixel art

Pixel art

is a form of

digital art
, created through the use of

raster graphics

software
,
where images are
edited on the

pixel

level. Graphics in most old (or relatively limited)
computer and video games,

graphing calculator

games, and many

mobile
phone

games are mostly pixel art.





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Vector graphics

Vector graphics

formats are complementary to

raster graphics
, which is the
representation of images as an array of

pixels
, as it is typically used for the
representation of photogr
aphic images

[4]

Vector graphics consists in encoding
information about shapes and colors that comprise the image, which can allow for
more flexibility in rendering. There are
instances when working with vector tools and
formats is best practice, and instances when working with raster tools and formats is
best practice. There are times when both formats come together. An understanding
of the advantages and limitations of each te
chnology and the relationship between
them is most likely to result in efficient and effective use of tools.


3D computer graphics

3D computer graphics

in contrast to

2D computer graphics

are graphics that use
a

three
-
dimensional

representation of geometric data that is stored in the computer
for the purposes of performing calculations and rendering 2D images. Such images
may be for later display or for real
-
time viewing.

Despite these differences, 3D comput
er graphics rely on many of the
same

algorithms

as 2D computer

vector graphics

in the

wire frame model
and 2D
computer

raster graphics

in the final rendered display. In computer graphics
software, the distinction between 2D and 3D is occ
asionally blurred; 2D applications
may use 3D techniques to achieve effects such as lighting, and primarily 3D may use
2D rendering techniques.

3D computer graphics are often referred to as

3D models
. Apart from the rendered
graphic, the model is contained within the graphical data file. However, there are
differences. A 3D model is the

mathematical

representation o
f any

three
-
dimensional

object. A model is not technically a graphic until it is visually displayed.
Due to

3D printing
, 3D models are not confined to virtual space. A model can be
displayed visually as a two
-
dimensional image through a process called

3D
rendering
,

or used in non
-
graphical

computer simulations

and calculations. There are
some

3D computer graphics software

for users

to create 3D images.





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Computer animation

Computer animation

is the art of creating moving images via the use of

computers
.
It
is a subfield of computer graphics and

animation
. Increasingly it is created by means
of

3D computer graphics
, though

2D computer graphics

are still widely used for
stylistic, low bandwidth, and faster real
-
time rendering needs. Sometimes the target
of the animation is the computer itself, but sometimes the target is ano
ther
medium
,
such as

film
. It is also referred to as CGI (
Computer
-
generated imagery

or computer
-
generated imaging), especially when used in films.

Virtual entities may contain and be controlled by assorted attributes, such as
transform values (location, orientation, and scale) stored in an
object's

transformation matrix
. Animation is the change of an attribute over time.
Multiple methods of achieving animation exist; the rudimentary form is based on the
creation and editing of

key frames
, each storing a value at a given time, per attribute
to be animated. The 2D/3D graphics software will

interpolate

between key frames,
creating an editable curve of a value mapped over time, resulting in animation. Other
methods of animation include

procedural

and

expression
-
based techniques: the
former consolidates related elements of animated entities into sets of attributes,
useful for creating

particle

effects and

crowd simulations
; the latter allows an
evaluated result returned from a user
-
defined logic
al expression, coupled with
mathematics, to automate animation in a predictable way (convenient for controlling
bone behaviour beyond what a

hierarchy

offers in

skeletal system

set up).

To create the illusion of movement, an image is displayed on the
computer

screen

then quickly repla
ced by a new image that is similar to the previous
image, but shifted slightly. This technique is identical to the illusion of movement
in

television

and

motion pictures
.




Research

Images are typically produced by


optical


devices; such as


cameras
,


mirrors
,

lenses
,

telescopes
,

microscopes
, etc. and natural objects and phenomena,
such as the

human eye

or water surfaces.





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A

digital image

is a representation of a two
-
dimensional

image

in binary format as a
sequence of ones and zeros. Digital images include both

vector

images
and

raster

images, but raster images are more commonly used. In digital imaging,

a

pixel

(or picture element) is a single point in a

raster image
. Pixels are normally
arranged in a regular 2
-
dimensional grid,
and are often represented using dots or
squares. Each pixel is a

sample

of an original image, where more samples typically
provide a more accurate representation of the origi
nal. The

intensity

of each pixel is
variable; in color systems, each pixel has typically three components such as

red,
green, and blue
.


Graphics

Graphics

are

visual

presentations on some surface, such as a wall,

canvas
,
computer screen, paper, or stone to

brand
, inform, illustrate, or entertain. Examples
are

photographs
,

drawings
,

line
art
,

graphs
,

diagrams
,

typography
,

numbers
,

symbols
,

geometric

designs,

maps
,
engi
neering drawings
, or other

images
. Graphics often combine

text
,

illustration
,
and

color
. Graphic design may consist of the deliberate selection, creation,
or
arrangement of typography alone, as in a brochure, flier, poster, web site, or book
without any other element. Clarity or effective communication may be the objective,
association with other cultural elements may be sought, or merely, the creation of a
distinctive style.


Rendering

Rendering is the process of generating an image from a

model

(or models in what
collectively could be called a

scene

file), by means of computer programs. A s
cene
file contains objects in a strictly defined language or data structure; it would contain
geometry, viewpoint,

texture
,
lighting
, and

shading

information as a description of the
virtual scene. The data contained in the scene file is then passed to a rendering
program to
be processed and output to a

digital image

or

raster graphics

image file.
The rendering program is usually built into the computer graph
ics software, though
others are available as plug
-
ins or entirely separate programs. The term "rendering"
may be by analogy with an "artist's rendering" of a scene. Though the technical




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details of rendering methods vary, the general challenges to overcome
in producing
a 2D image from a 3D representation stored in a scene file are outlined as
the

graphics pipeline

along a rendering device, such as a

GPU
. A GPU is a purpose
-
built device able to assist a

CPU

in performing complex rendering calculations. I
f a
scene is to look relatively realistic and predictable under virtual lighting, the rendering
software should solve the

rendering equation
. The rendering equation doesn't
account for all lig
hting phenomena, but is a general lighting model for computer
-
generated imagery. 'Rendering' is also used to describe the process of calculating
effects in a video editing file to produce final video output.


3D projection

3D projection

is a method of mapping three dimensional points to a two dimensional
plane. As most current methods for displaying graphical data are based on planar
two dimensional media, the use of t
his type of projection is widespread, especially in
computer graphics, engineering and drafting.


Ray tracing

Ray tracing

is a technique for generating an

image

by tracing the path
of

light

through

pixels

in an

image plane
. The technique is capable of producing a
very high degree of
photorealism
; usually higher than that of typical

scanline
rendering

methods, but at a greater

computational cost
.


Shading

Sh
ading

refers to

depicting

depth in

3D models

or illustrations by varying levels
of

darkness
. It is a process used in drawing for depicting levels of darkness on paper
by applying media more densely or with a darker shade for darker areas, and less
densely or with a lighter shade for lig
hter areas. There are various techniques of
shading including

cross hatching

where perpendicular lines of varying closeness are
drawn in a grid pattern to shade an area. The closer the lin
es are together, the
darker the area appears. Likewise, the farther apart the lines are, the lighter the area
appears. The term has been recently generalized to mean that

shaders

are applied.





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Texture mapping

Texture mapping

is a method for adding detail, surface texture, or colour to
a

computer
-
generated graphic

or

3D model
. Its application to 3D graphics was
pioneered by Dr

Edwin Catmull

in 1974. A texture
map is applied (mapped) to the
surface of a shape, or polygon. This process is akin to applying patterned paper to a
plain white box. Multitexturing is the use of more than one texture at a time on a
polygon.
[6]

Procedural textures

(created from adjusting parameters of an underlying
algorithm that produces an output texture), and

bitmap textures

(created in an

image
editing

application) are, generally speaking, common methods of implementing
texture definition from a 3D
animation program, while intended placement of textures
onto a model's surface often requires a technique known as

UV mapping
.


Anti
-
aliasing

Rendering resolution
-
independent entities (such as 3D
models) for viewing on a
raster (pixel
-
based) device such as a

LCD display

or

CRT television

inevitably
causes

aliasing artifacts
mostly along geometric edges and the boundaries of texture
details; these artifacts are informally called "
jaggies
". Ant
i
-
aliasing methods rectify
such problems, resulting in imagery more pleasing to the viewer, but can be
somewhat computationally expensive. Various anti
-
aliasing algorithms (such
as

supersampling
) a
re able to be employed, then customized for the most efficient
rendering performance versus quality of the resultant imagery; a graphics artist
should consider this trade
-
off if anti
-
aliasing methods are to be used. A pre
-
anti
-
aliased

bitmap texture

being displayed on a screen (or screen location) at a
resolution different than the resolution of the texture itself (such as a textured model
in the distance from the virtual camera) will exhibit a
liasing artifacts, while
any

procedurally
-
defined texture

will always show aliasing artifacts as they are
resolution
-
independent; techniques such as
mipmapping

and

texture filtering

help to
solve texture
-
related aliasing problems.





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Volume rendering

Volume rendering

is a technique used to display a

2D projection

of a 3D
discretely

sampled

data set
. A typical 3D data set is a group of 2D slice images
acquired by a

CT

or

MRI

scanner.

Usually these are acquired in a regular pattern (e.g., one slice every
milli
metre
) and
usually have a regular number of image

pixels

in a regular pattern. This is an
example of a regular volumetric grid, with each volume element,
or

voxel

represented by a single value that is obtained by sampling the immediate
area surrounding the voxel.


3D
modelling

3D
modelling

is the process o
f developing a mathematical,

wireframe

representation
of any three
-
dimensional object, called a "3D model", via specialized software.
Models may be created automatically or

manually; the manual
modelling

process of
preparing geometric data for 3D computer graphics is similar to

plastic arts

such
as

sculpting
. 3D models may be created using multiple approaches: use
of

NURBS

curv
es to generate accurate and smooth surface patches,

polygonal
mesh
modelling

(manipulation of faceted geometry), or polygonal
mesh

subdivision
(advanced tessellation of polygons, resulting in smooth surfaces
similar to NURBS models). A 3D model can be displayed as a two
-
dimensional
image through a process called

3D rendering
.


Pioneers in graphic design


Charles Csuri

Charles Csuri

is a pioneer in computer animation and digital fine art and created the
first computer
art in 1964. Csuri was recognized by

Smithsonian

as the father of
digital art and computer animation, and as a pioneer of computer animation by
the

Museum of Modern Art

(MoMA) and

Association for Computing Machinery
-
SIGGRAPH
.





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Donald P. Greenberg

Donald P. Greenberg

is a leading innovator in computer graphics. Greenberg has
authored hundreds of articles and served as a teacher and mentor to man
y
prominent computer graphic artists, animators, and researchers such as

Robert L.
Cook
,

Marc Levoy
, and

Wayne Lytle
. Many of his former students have won
Academy Awards for technical achievements and several have won
the

SIGGRAPH

Achievement Award. Greenberg was the founding director

of the
NSF Center for Computer Graphics and Scientific Visualization.


A. Michael Noll

Noll

was one of the first researchers to use a

digital

computer

to create artistic
patterns and to formalize the use of random processes in the creation of

visual arts
.
He began
creating digital computer art in 1962, making him one of the earliest digital
computer artists. In 1965, Noll along with Frieder Nake and Georg Nees were the
first to publicly exhibit their computer art. During April 1965, the Howard Wise Gallery
exhibited

Noll's computer art along with random
-
dot patterns by

Bela Julesz
.


Other pioneers



Jim Blinn



Arambilet



Benoît B. Mandelbrot



Henri Gouraud



Bui Tuong Phong



Pierre Bézier



Paul de Casteljau



Daniel J. Sandin



Alvy Ray Smith



Ton Roosendaal



Ivan Sutherland





Page
17





Computer graphics

studies the manipulation of visual and geometric information
using computational techniques.

It focuses on
the

mathematical

and

computational

foundations of image generation and
processing rather than purely

aesthetic

issues. Computer graphics is often
differentiated from the field of

visualizati
on
, although the two fields have many
similarities.

Connected studies include:



Scientific visualization



Information

visualization



Computer vision



Image processing



Computational Geometry



Computational Topology



Applied mathematics


Applications of computer graphics include:



Special effects



Visual effects



Video games



Digital art


Subfields in computer graphics

A broad classification of major subfields in computer graphics might be:

1.

Geometry: studies ways to represent and process surfaces

2.

Animation: studies with
ways to represent and manipulate motion

3.

Rendering: studies algorithms to reproduce light transport

4.

Imaging: studies image acquisition or image editing





Page
18




Geometry


The subfield of geometry studies the representation of three
-
dimensional objects in a
discrete

digital setting. Because the appearance of an object depends largely on its
exterior,

boundary representations

are most commonly used. Two
dimensional

surfaces

are a good representation for most objects, though they may
be non
-
manifold
. Since surfaces are not finite, discrete digital approxim
ations are
used.

Polygonal meshes

(and to a lesser extent

subdivision surfaces
) are by f
ar the
most common representation, although point
-
based representations have become
more popular recently (see for instance the

Symposium on Point
-
Based Graphics
).
These representations are

Lagrangian,

meaning the spatial locations of the samples
are independent. Recently,

Eulerian

surface descriptions (i.e., where spatial samples
are fixed) such as

level sets

have been developed into

a useful representation for
deforming surfaces which undergo many topological changes (with

fluids

being the
most notable example
).


Geometry Subfields



Implicit surface modeling
-

an older subfield which examines the use of algebraic
surfaces,

constructive so
lid geometry
, etc., for surface representation.



Digital geometry processing
-

surface reconstruction
, simplification, fairing, mesh
repair,

parameterization
, remeshing,

mesh generation
, surface compression, and
surface editing all fall under t
his heading.




Discrete differential geometry
-

a nascent field which defines geometric quantities for
the discrete surfaces used in computer graphics.




Point
-
based graphics
-

a recent field which focuses on points as the fundamental
representation of surfa
ces.



Subdivision surfaces





Page
19






Out
-
of
-
core mesh processing
-

another recent field which focuses on mesh datasets
that do not fit in main memory.


Animation

The subfield
of animation studies descriptions for surfaces (and other phenomena)
that move or deform over time. Historically, most work in this field has focused on
parametric and data
-
driven models, but recently

physical simulation

has become
more popular as computers have become more powerful computationally.


Subfields



Performance capture



Character animation



Physical simulati
on (e.g.

cloth modelling
, animation of

fluid dynamics
, etc.)

Rendering


Rendering generates images from a model. Rendering may simulate

light
transport

to create realistic images or it may create images that have a particular
artistic style in

non
-
photorealistic rendering
. The two basic operations in realistic
rendering are transport (how much light passes from one place to another) and
scattering (how surfaces interact with light). See

Rendering (computer graphics)

for
more information.






Page
20




Transport

Transport

describes how illumination in a scene gets from
one place to
another.

Visibility

is a major component of light transport.


Scattering

Models of

scattering

and

shading

are used to describe the appearance of a su
rface.
In graphics these problems are often studied within the context of rendering since
they can substantially affect the design of rendering algorithms. Shading can be
broken down into two orthogonal issues, which are often studied independently:

1.

scattering

-

how light interacts with the surface

at a given point

2.

shading

-

how material properties vary across the surface

The former problem refers to

scattering
, i.e., the relationship between
incoming and
outgoing illumination at a given point. Descriptions of scattering are usually given in
terms of a

bidirectional scattering distribution function

or BS
DF. The latter issue
addresses how different types of scattering are distributed across the surface (i.e.,
which scattering function applies where). Descriptions of this kind are typically
expressed with a program called a

shader
. (Note that there is some confusion since
the word "shader" is sometimes used for programs that describe
local

geometric

variation.)


Other subfields



P
hysically
-
based rendering
-

concerned with generating images according to the
laws of

geometric optics
.



R
eal time rendering

-

focuses on rendering for interactive applications, typicall
y using
specialized hardware like

GPUs
.



N
on
-
photorealistic rendering
.



R
elighting
-

recent area concerned with quickly re
-
rendering scenes
.






Page
21




Geometry processing


Geometry processing
, or mesh processing, is a fast
-
growing area of

research

that
uses concepts from

applied mathematics
,

computer science

and

engineering

to
design efficient

algorithms

for the acquisition, reconstruction, analysis, manipulation,
simulation and transmission of complex 3D models. Applications of geometry
processing algorithms already cover a
wide range of areas
from

multimedia
,

entertainment

and classical

computer
-
aided design
, to

biomedical
computing
,

rev
erse engineering

and

scientific computing
.


Cloth modelling


Cloth modelling

is the term used for simulating cloth within a computer program
usually in the realm of

computer graphics

. The main approaches used for this may
be classified into three basic types: geometric, physical, and particle/energy.


Most models of cloth are based on "particles" of mass

connected together in some
manner of mesh.

Newtonian Physics

is used to model each particle through the use
of a "black box" called a

physics engine
. This involves using the basic law of motion
(Newton's Second Law):


In all of these models, the goal is to find the position and shape of a piece of fabric
using this basic equation and several other methods.

Geometric methods

Weil pioneered the first of these, the geometric technique, in 1986.
[1]

His work was
focused on approximating the look of cloth by treating cloth like a

collection of cables
and using

Hyperbolic cosine

(catenary) curves. Because of this, it is not suitable for
dynamic models but works very well for stationary or single
-
f
rame renders

[1]
. This
technique creates an underlying shape out of single points; then, it parses through




Page
22




each set of three of these points and maps a catenary curve to
the set. It then takes
the lowest out of each overlapping set and uses it for the render.


Physical methods

The second technique treats cloth like a grid work of particles connected to each
other by springs. Whereas the geometric approach accounted for
none of the
inherent stretch of a woven material, this physical model accounts for stretch
(tension), stiffness, and weight:

E
(
Particle
i
,
j
) =

k
s
E
s
,
i
,
j

+

k
b
E
b
,
i
,
j

+

k
g
E
g
,
i
,
j



s terms are elasticity (by

Hooke's Law
)



b terms are bending



g terms are gravity (see

Acceleration due to gravity
)

Now we appl
y the basic principle of

mechanical equilibrium

in which all bodies seek
lowest energy by differentiating this equation to find the minimum energy.


Particle/energy methods

The last method

is more complex than the first two. The particle technique takes the
physical technique from (f) a step further and supposes that we have a network of
particles interacting directly. That is to say, that rather than springs, we use the
energy interactions

of the particles to determine the cloth’s shape. For this we use an
energy equation that adds on to the following:

U
Total

=

U
Repel

+

U
Stretch

+

U
Bend

+

U
Trellis

+

U
Gravity



The energy of repelling is an artificial element we add to prevent
cloth from
intersecting itself.



The energy of stretching is governed by

Hooke's law

as with the
Physical Method.



The energy of bending describes the stiffness of the fabric



The energy of trellising describes
the shearing of the fabric
(distortion within the plane of the fabric)





Page
23






The energy of gravity is based on

acceleration due to gravity

We can also add terms for energy added
by any source to this equation, then derive
and find minima, which generalizes our model. This allows us to model cloth
behaviour under any circumstance, and since we are treating the cloth as a
collection of particles its behaviour can be described with t
he dynamics provided in
our physics engine.


Dynamics

Soft body dynamics

Soft body

dynamics

is a field of

computer graphics

that focuses on visually realistic
physical

simulations

of the motion and properties of

deformable

objects (or

soft
bodies). The applications are mostly in video games and film. Unlike in simulation
of

rigid bodies
, the shape of soft bodies can change, meaning that the relative
distance of two points on the object is not fixed. While the relative distances of points
are not fixed, the body is expected to retain its shape
to some degree (unlike a

fluid
).
The scope of soft body dynamics is quite broad, including simulation of soft organic
materials such as muscle, fat, hair and vegetation, as well as other deformable
materia
ls such as clothing and fabric. Generally, these methods only provide visually
plausible emulations rather than accurate scientific/engineering simulations, though
there is some crossover with scientific methods, particularly in the case of finite
element
simulations. Several

physics engines

currently provide software for soft
-
body simulation.

Deformable solids

The simulation of volumetric solid soft bodies can be realised by
using a variety of
approaches.

Mass
-
spring models






Page
24




In this approach, the body is modeled as a set of point masses (nodes) connected by
ideal weightless

elastic

springs

obeying some variant of
Hooke's law
. The nodes may
either derive from the edges of a two
-
dimensional

polygonal mesh

representation of
the surface of
the object, or from a three
-
dimensional network of nodes and edges
modeling the internal structure of the object (or even a one
-
dimensional system of
links, if for example a rope or hair strand is being simulated). Additional springs
between nodes can be a
dded, or the force law of the springs modified, to achieve
desired effects. Applying

Newton's second law

to the point masses including the
forces applied by the spr
ings and any external forces (due to contact, gravity, air
resistance, wind, and so on) gives a system of

differential equations

for the motion of
the nodes, wh
ich is solved by standard numerical schemes for solving

ODEs
.

Rendering of a three
-
dimensional mass
-
spring lattice is often done using

free form

deformation, in which the rendered mesh is embedded in the lattice and distorted to
conform to the shape of the lattice as it evolves.

Finite element simulation

This is a more physically accurate approach, which uses the widely used

finite
element method

to solve the

partial differential equations

which govern the dynamics
of an

elastic material
. The body is modeled as a three
-
dimensional

elastic
continuum

by breaking it into a large number of solid elements which fit together, and
solving for the

stresses

and

strains

in each element using a model of the material.

The elements are typically tetrahedral, the nodes being the vertices of
the tetrahedra
(relatively simple methods exist
[10]
[11]

to

tetrahedralize

a three dimensional

region
bounded by a polygon mesh into

tetrahedra
, similarly to how a two
-
dimensional

polygon

may be

triangulated

into triangles). The

strain

(which measures
the local

deformation of the points of the material from their rest state) is quantified
by the

strain tensor

. The

stress

(which measures the local forces per
-
unit area in
all directions acting on the material) is quantified by the

stress tensor

. Given the
current local strain, the local stress can be computed via the generalized form
of

Hooke's law
:


where


is the "
elasticity tensor
" which encodes the
material properties (parametrized in linear elasticity for an isotropic material by
the

Poisson ratio

and

Young's modulus
).





Page
25




The equation of motion of the element nodes is obtained by integrating the stress
field over each element and relati
ng this, via

Newton's second law
, to the node
accelerations.

Pixelux (developers of the

Digita
l Molecular Matter

system) use a finite
-
element
-
based approach for their soft bodies, using a tetrahedral mesh and converting the
stress tensor directly into node forces. Rendering is done via a form of

free form
deformation
.


Energy minimization methods

This approach is motivated by

variational principles

and the physics of surfaces,
which dictate that a constrained surface will assume the shape which

minimizes the
total energy of

deformation

(analogous to a

soap bubble
). Expressing the energy of a
surface in terms of its local deformation (the energy is due to a combination of
stretching and bending), the local force on the surface is given by differentiating the
energy with respect to positi
on, yielding an equation of motion which can be solved
in the standard ways.


Shape matching

In this scheme, penalty forces or constraints are applied to the model to drive it
towards its original shape

(i.e. the material behaves as if it has

shape memory
). To
conserve momentum the rotation of the body must be estimated properly, for
example via

polar decom
position
. To approximate finite element simulation, shape
matching can be applied to three dimensional lattices and multiple shape matching
constraints blended.


Rigid
-
body based deformation

Deformation can also be handled by a traditional rigid
-
body

physics engine
,
modelling

the soft
-
body motion using a network of multiple rigid bodies connected by
constraints, and using (for example)

matrix
-
palette skinning

to generate a surface
mesh for rendering. This is the approach used for deformable objects in

Havoc
.






Page
26




Cloth simulation

In the context of computer graphics,

cloth simulation

refers to the simulation of soft
bodies in the form of two dimensional continuum elastic membranes, that is, for this
purpose, the actual structure of real

cloth

on the

yarn

level can be ignored (though
modelling

cloth on the yarn level has been tried). Via

rendering

effects, this is
capable of producing a visually plausible emulation of

textiles

and

clothing
, used in a
variety of contexts in video games, animation, and film. It can also be used to
simulate two dimensional sheets of materials other than textiles, such as deformable
me
tal panels or vegetation. In video games it is often used to enhance the realism of
clothed characters, which otherwise would be entirely

animated
.

Cloth simulators are

generally based on

mass
-
spring models
, but a distinction must
be made between force
-
based and position
-
based solvers.


Force
-
based cloth

The

mass
-
spring model

(obtained from a

polygonal mesh

representation
of the cloth)
determines the internal spring forces acting on the nodes at each time step (in
combination with gravity and applied forces). Newton's second law gives equations
of motion which can be solved via standard

ODE

solvers. To create high resolution
cloth with a realistic stiffness is not possible however with simple

explicit

solvers
(such as forward

Euler integration
), unless the time step is made too small for
interactive applications (since as i
s well known,

explicit

integrators are numerically
unstable for sufficiently

stiff

systems). Therefore

implicit solvers

must be used,
requiring solution of a large

sparse matrix

system (via e.g. the

conjugate gradient
method
), which itself may also be difficult to achieve at interactive fram
e rates. An
alternative

is to use an explicit method with low stiffness, with

ad hoc

methods to
avoid instability and excessive stretching (e.g. strain limiting corrections).


Position
-
based dynamics

To avoid needing to do an expensive implicit solution of

a system of

ODEs
, many
real
-
time cloth simulators (notably

PhysX
,

Havok Cloth
, and

Maya nCloth
)
use

position based dynamics
(
PBD), an approach based on constraint relaxation. The
mass
-
spring model is converted into a system of constraints, which demands that




Page
27




the distance between the connected nodes be equal to the initial distance. This
system is solved sequentially and iterativ
ely, by directly moving nodes to satisfy each
constraint, until sufficiently stiff cloth is obtained. This is similar to a

Gauss
-
Seidel

solution of the implicit matrix system for t
he mass
-
spring model. Care must be
taken though to solve the constraints in the same sequence each timestep, to avoid
spurious oscillations, and to make sure that the constraints do not
violate

linear

and

angular momentum

conservation. Additional position constraints
can be
applied, for example to keep the nodes within desired regions of space
(sufficiently close to an animated model for example), or to maintain the body's
overall shape via shape matching.


Collision detection for deformable objects

Collision detection

Realistic interaction of simulated soft objects with their environment may be
important for obtaining visually realistic results. Cloth self
-
intersection is important in
some applications for accep
tably realistic simulated garments. This is challenging to
achieve at interactive frame rates, particularly in the case of detecting and resolving
self collisions and mutual collisions between two or more deformable objects.

Collision detection may be

disc
rete/a posteriori

(meaning objects are advanced in
time through a pre
-
determined interval, and then any penetrations detected and
resolved), or
continuous/a priori

(objects are advanced only until a collision occurs,
and the collision is handled before proc
eeding). The former is easier to implement
and faster, but leads to failure to detect collisions (or detection of spurious collisions)
if objects move fast enough. Real
-
time systems generally have to use discrete
collision detection, with other

ad hoc

ways

to avoid failing to detect collisions.

Detection of collisions between cloth and environmental objects with a well defined
"inside" is straightforward since the system can detect unambiguously whether the
cloth mesh vertices and faces are intersecting the

body and resolve them
accordingly. If a well defined "inside" does not exist (e.g. in the case of collision with
a mesh which does not form a closed boundary), an "inside" may be constructed via




Page
28




extrusion. Mutual
-

or self
-
collisions of soft bodies defined

by tetrahedra is
straightforward, since it reduces to detection of collisions between solid tetrahedra.

However, detection of collisions between two polygonal cloths (or collision of a cloth
with itself) via discrete collision detection is much more diffi
cult, since there is no
unambiguous way to locally detect after a time step whether a cloth node which has
penetrated is on the "wrong" side or not. Solutions involve either using the history of
the cloth motion to determine if an intersection event has oc
curred, or doing a global
analysis of the cloth state to detect and resolve self
-
intersections.

Pixar

has
presented a method which uses a global topological analysis of mesh intersections
in configuration
space to detect and resolve self
-
interpenetration of cloth. Currently,
this is generally too computationally expensive for real
-
time cloth systems.

To do collision detection efficiently, primitives which are certainly not colliding must
be identified as so
on as possible and discarded from consideration to avoid wasting
time. To do this, some form of

spatial subdivision

scheme is essential, to avoid a
brute force test o
f

O
[
n
2
]

primitive collisions. Approaches used include:



Bounding volume hierarchies

(
AABB

trees,

OBB

trees, sphere trees)



Grids, either uniform

(using

hashing

for memory efficiency) or hierarchical
(e.g.

Octree
,

kd
-
tree
)



Coherence
-
e
xploiting schemes, such as

sweep and prune

with insertion sort, or
tree
-
tree collisions with front tracking.



Hybrid methods involving a combination of various of these schemes, e.g. a
coarse AABB

tree plus sweep
-
and
-
prune with coherence between colliding
leaves.


Other effects which may be simulated via the methods of soft
-
body dynamics are:



Destructible

materials:

Fracture

of brittle solids,

cutting

of soft bodies,
and

tearing

of cloth. The

finite element method

is especially suited to modelling
fracture

as it includes a realistic model of the distribution of internal stresses
in
the material, which physically is what determines when fracture occurs, according
to

fracture mechanics
.



Plasticity

(permanent deformation) and

melting





Page
29






Simulated hair, fur, and feathers



Simulated organs for biomedical applications

Simulation of fluids in the context of computer graphics

would not normally be
considered soft
-
body dynamics, which is usually restricted to mean simulation of
materials which have a tendency to retain their shape

and form. In contrast,
a

fluid

assumes the shape of whatever vessel contains it, as the particles are bound
together by relatively weak forces.


Rigid body dynamics


In

physics
,

rigid body dynamics

is the study of the

motion

of

rigid bodies
.
Unlike

particles
, which move only in three

degrees of freedom

(
translation

in three
directions), rigid bodies occupy space and have geomet
rical properties, such as
a

centre of mass
,

moments of inertia
, etc., that characterize motion in six

degrees of
freedom

(translation in three directions plus

rotation

in three directions). Rigid bodi
es
are also characterized as being non
-
deformable, as opposed to

deformable bodies
.
As such,

rigid body dynamics

is used heavily in analyses and

computer
simulations

of physical systems and machinery where rotational motion is important,
but

material deformation

does not have a significant effect on the motion of the
system.


Rigid body linear momentum

Newton's Second Law

states that the rate of change of the

linear momentum

of a
particle with constant

mass

is equal to the sum of all external

forces

acting on the
particle:


where

m

is the particle's mass,

v

is the particle's velocity, their product

m
v

is the
linear momentum, and

f
i

is one of the

N

number of forces acting on the particle.





Page
30




Because the mass is constant, this is equivalent to


To generalize, assume a body of finite mass and size is composed of such particles,
each with

infinitesimal

mass d
m
. Each particle

has

a position vector

r
. There exist
internal forces, acting between any two particles, and external forces, acting only on
the outside of the mass. Since velocity

v

is the

derivative

of position

r
, the derivative
of velocity d
v
/d
t

is the second derivative of position d
2
r
/dt
2
, and the linear momentum
equation of any given particle is


When the linear momentum equations fo
r all particles are added together, the
internal forces sum to zero according to

Newton's third law
, which states that any
such force has opposite magnitudes on the
two particles. By accounting for all
particles, the left side becomes an integral over the entire body, and the second
derivative operator can be moved out of the integral, so

.

Let

M

be the total mass, which is constant, so the left side can be multiplie
d and
divided by

M
, so

.

The expression


is the formula for the position of the

centre of mass
.
Denoting this by

r
cm
, the equation reduces to






Page
31




Thus, linear momentum equations can be extended to

rigid bodies

by denoting that
they describe the motion of the

centre of mass

of the body. This is known as

Euler's
first law
.


Rigid body angular momentum

The most general equation for rotation of a rigid body in three dimensions about an
arbitrary origin

O

with axes

x
,

y
,

z

is


where the

moment of inertia tensor
,

, is given by



Given that

Euler's rotation theorem

states that there is always an

instantaneous axis
of rotation
, the

angular velocity
,

, can be

given by a vector over this axis


where


is a set of mutually

perpendicular

unit vectors

fixed in a

reference
frame
.

Rotating a rigid body is equivalent to rotating a

Poinsot ellipsoid
.


Angular momentum and torque

Similarly, the

angular momentum


for a system of particles with linear
momenta

p
i

and distances

r
i

from the rotation axis is defined






Page
32




For a rigid body rotating with angular velocity

ω

about
the rotation axis


(a

unit
vector
), the velocity vector


may be written as a

vector cross product


Where

a
ngular velocity vector



is the shortest vector from the rotation axis to the point mass.

Substituting the formula for


into the definition of


yields


Where we have introduced the special case that the position vectors of all particles
are
perpendicular to the rotation axis (
e.g.,

a

flywheel
):

.

The

torque


is defined as the rate of change of the angular momentum



If I is constant
(because the inertia tensor is the identity, because we work in the
intrinsically frame, or because the torque is driving the rotation around the same
axis


so that

I

is not changing) then we may write


Where

α

is called the

angular acceleration

(or

rota
tional acceleration
) about the
rotation axis
.

Notice that if I is not constant in the external reference frame (i.e. the three main
axes of the body are different) then we cannot take the I outside the derivate. In
these cases we can have
torque
-
free precession
.

Applications

Computer

physics engines

use rigid body dynamics to increase

interactivity and
realism in

video games
.






Page
33




No index entries found.
Use of advanced computer g
raphics

in

architectural draughting.

AUTOCAD

AutoCAD

is a

CAD

(Computer Aided Design or Computer Aided Drafting)

software
applicat
ion

for

2D

and

3D

de
sign

and

drafting
. It is developed and sold by

Autodesk,
Inc.

First released in December 1982, AutoCAD

was one of the first CAD programs
to run on

personal computers
, notably the

IBM PC
. At that time, most
other CAD
programs ran on

mainframe computers

or

mini
-
computers

which were connected to
a gr
aphics

computer terminal

for each user. AutoCad and its vertical products are
incompatible with

Bit

Defender

security software
.


Early r
eleases of AutoCAD used primitive entities


lines, poly

lines, circles, arcs,
and text


to construct more complex objects. Since the mid
-
1990s, AutoCAD has
supported custom objects through its C++

Application Programming Interface

(API).
Modern AutoCAD includes a full set of basic

solid modelling

and 3D tools. With the
release of
AutoCAD 2007 came improved 3D modelling, which meant better
navigation when working in 3D. Moreover, it became easier to edit 3D models.
The

mental ray

engine

was included in

rendering
, it was now possible to do quality
renderings. AutoCAD 2010 introduced
parametric functionality and mesh modelling.

AutoCAD supports a number of APIs for customization and automation. These
include

AutoLISP
,

Visual LISP
,

VBA
,

.NET

and

Object

ARX
. Object

ARX is
a

C++

class library, which was also the base for products extending AutoCAD
functionality to specific fields, to create products such as AutoCAD Archite
cture,
AutoCAD Electrical, AutoCAD Civil 3D, or third
-
party AutoCAD
-
based applications.

AutoCAD
and AutoCAD LT are available
for

English
,

German
,

French
,

Italian
,

Spanish
,

Japanese
,

Korean
,

Chinese
Simplified
,

Chinese Traditional
,

Russian
,

Czech
,

Polish
,

Hungarian
,

Brazilian
Portuguese
,

Danish
,

Dutch
,

Swedish
,

Finnish
,

Norwegian
, and

Vietnamese
. The
extent of localization varies from full translation of the product to documentation only.
The AutoCAD command set is localized as a part of the software localization.






Page
34




AutoCAD origin

AutoCAD was derived from a pr
ogram called Interact, which was written in a
proprietary language (SPL) and ran on the Marinchip Systems 9900 computer
(Marinchip was owned by Autodesk co
-
founders

John Walker

and Dan Drake.)

When Marinchip Software Partners (later to be renamed Autodesk) was formed, they
decided to re
-
code Interact in C and

PL/1

--

C, because it seemed to be the bi
ggest
upcoming language, and PL/1. In the end, the PL/1 version was unsuccessful. The C
version was, at the time, one of the most complex programs in that language to date.
Autodesk even had to work with the compiler developer (Lattice) to fix certain
limi
tations to get AutoCAD to run.


AutoCAD LT

AutoCAD LT is a lower cost version of AutoCAD with reduced capabilities first
released in November 1993. AutoCAD LT, priced at $495, became the first product
in the company's history priced below $1000 to bear
the name "AutoCAD". In
addition to being sold directly by Autodesk, it can also be purchased at computer
stores, unlike the full version of AutoCAD which must be purchased from official
Autodesk dealers. Autodesk developed AutoCAD LT so that they would hav
e an
entry
-
level CAD package to compete in the lower price level.

As of the 2011 release the AutoCAD LT MSRP has risen to $1200. While there are
hundreds of small differences between the full AutoCAD package and AutoCAD LT,
currently there are a few recogn
ized major differences

in the software's features:



3D Capabilities: AutoCAD LT lacks the ability to create, visualize and render 3D
models as well as 3D printing.



Network Licensing: AutoCAD LT cannot be used on multiple machines over a
network.



Customizati
on: AutoCAD LT does not support customization with LISP, ARX, and
VBA.



Management and automation capabilities with Sheet Set Manager and Action
Recorder.





Page
35






CAD standards management tools.


AutoCAD Freestyle

Built on the AutoCAD platform,

AutoCAD Freestyle

is a simplified, low
-
cost (US$149)
application that makes it easy to create accurate, professiona
l
-
looking 2D drawings
and sketches.


Student versions

AutoCAD is licensed at a significant discount over commercial retail pricing to
qualifying students and teachers, with a 36
-
month license available. The student
version of AutoCAD is functionally identi
cal to the full commercial version, with one
exception: DWG files created or edited by a student version have an internal bit
-
flag
set (the "educational flag"). When such a DWG file is printed by any version of
AutoCAD (commercial or student), the output w
ill include a plot stamp / banner on all
four sides. Objects created in the Student Version cannot be used for commercial
use. These Student Version objects will "infect" a commercial version DWG file if
imported
.


The

Autodesk student community

provides registered students with free access to
different Autodesk applications.


Vertical programs

Autodesk has also developed a few vertical programs, for discipline
-
specific
enhancements.

AutoCAD Architecture

(formerly Architectural Desktop), for example,
permits architectural designers to draw 3D objects such as walls, doors and
windows, with more intelligent data associated w
ith them, rather than simple objects
such as lines and circles. The data can be programmed to represent specific
architectural products sold in the construction industry, or extracted into a data file
for pricing, materials estimation, and other values rel
ated to the objects represented.
Additional tools allow designers to generate standard 2D drawings, such as
elevations and sections, from a 3D architectural model. Similarly, Civil Design, Civil




Page
36




Design 3D, and Civil Design Professional allow data
-
specific
objects to be used,
allowing standard civil engineering calculations to be made and represented
easily.

AutoCAD Electrical
, AutoCAD Civil 3D, AutoCAD Map 3D,

AutoCAD
Mechanical
, AutoCAD MEP, AutoCAD P&ID, AutoCAD Plant 3D and AutoCAD
Structural detailing are other examples of industry
-
specific CAD applications built on
the AutoCAD platform.


AutoCAD Architec
ture


AutoCAD Architecture

(abbreviated as ACA) is a version of

Autodesk
's flagship
product,

AutoCAD
, with tools and functions specially suited to

architectural

work.

Architectural objects have a relationship to one another and interact with each other
intelligently. For example, a window has a relationship to the wall that con
tains it. If
you move or delete the wall, the window reacts accordingly. Objects can be
represented in both 2D and 3D.

In addition, intelligent architectural objects maintain dynamic links with construction
documents and specifications, resulting in more a
ccurate project deliverables. When
someone deletes or modifies a door, for example, the door schedule can be
automatically updated. Spaces and areas update automatically when certain
elements are changed, calculations such as square footage are always up t
o date.

AutoCAD Architecture uses the

DWG

file format but an object enabler

is needed to
access, display, and manipulate object data in applications different from AutoCAD
Architecture.

AutoCAD
Architecture was formerly known as AutoCAD Architectural Desktop (often
abbreviated ADT) but Autodesk changed its name for the 2008 edition. The change
was made to better match the names of Autodesk's other discipline
-
specific
packages, such as

AutoCAD Electrical

and

AutoCAD Mechanical
.





Page
37





Autodesk Maya

Maya

was originally a next
-
generation animation product
under development at Alias
Research, Inc. based on code from a previous Alias product,

Alias Sketch!
, a 3D
modeler and renderer for the

Macintosh

that lacked animation features. The code
was ported to

IRIX

and animation features were added. The codename for this
porting project was

Maya
.
[4]

Walt Disney Feature Animation

collaborated closely with
Maya's development during its production of

Din
osaur
.
[5]

Disney requested that
the

User interface

of the application be customizable so that a personalized workf
low
could be created. This was a particular influence in the open architecture of

Maya
,
and partly responsible for it's becoming so popular in the industry.

After

Silicon Graphics Inc.

acquired both Alias and

Wavefront Technologies, Inc.
,
Wavefront's next
-
generation technology (then under development) was merged into
May
a. SGI's acquisition was a response to

Microsoft
Corporation

acquiring

S
oftimage, Co.
. The new wholly
-
ow
ned subsidiary was named
"Alias
Wavefront

.

In the early days of development, Maya started with

Tcl

as the scripting language, in
order to leverage its similarity to a Unix sh
ell language. But after the merger with
Wavefront Sophia, the scripting language in Wavefront's

Dynamation
, was chosen
as the basis of MEL (Maya embedded language
).


Maya 1.0 was released in February 1998. Alias was successful in expanding its
market share, with leading visual effects companies such as

Industrial

Light and
Magic

and

Tippett Studio

switching from

SoftImage

to

Maya
.

Following a series of acquisitions, Maya was bought by Autodesk in 2005.

Under the
name of the new parent company,

Maya

was
renamed