Using AVS/Express in an Introductory Computer

Graphics Course

2

Course Structure

• Undergraduate course is a modular scheme

• Students study 8 modules per year, each one for 15 weeks, for 3 years

• Second year: Tools for Graphics and Visualisation

• Third year: Methods for Graphics and Visualisation

3

Tools for Graphics and Visualisation

• Uses 2D images to implement some of the standard algorithms in computer graphics:-– draw a circle– rotate, scale, and translate a 2D shape– window to viewport transformation– calculate co-ordinates of intersection of 2 lines– zoom in and out, & pan up/down/left/right – Bezier Curve drawing to fit 4 points

4

Visualisation component

• Create 3D shape from either: -

– 2D profile

– surface co-ordinates

• Use AVS/Express to visualise the 3D shape• Use AVS/Express to animate the 3D shape

5

Draw a Circle

• The co-ordinates of any point on the edge of a circle centred at the origin may be obtained from the following equations: -

• X = Radius*cosine() • Y = Radius*sine()• where is the angle in radians between the X axis

and a point on the circle (in an anti-clockwise direction)

6

Draw a Circle

=degrees*/180

X = Radius*cosine()

Y = Radius*sine()

X-axis

Y-axis

Radius

7

Create 3D solid from 2D profile

Profile

Y

X

Solid of revolutionof bottle

shape

Y

X

Z

8

Create 3d solid from 2D profile

• The students use the circle code to generate the X and Z co-ordinates (the Y co-ordinates remain constant for each point on the profile)

• They also have to generate an extra set of co-ordinates (exactly the same as the first set) to make AVS/Express join the last point up to the first one.

9

Surface Plot

• Specify a regular grid for the (x,y,z) co-ordinates

• Student has to generate a height for each co-ordinate based on a random number

10

a b

c

3D Surface

• Randomly modify its new height within limits

• Create a new mid-way point

• Make its height the average of the adjacent points

11

Include the diagonals

• Also along the diagonals based on the heights of the four corners (a, b, c, and d)

a b

d c

12

13

Field file for a bottle

# AVS field file

# bottle

ndim = 2

dim1 = 21

dim2 = 15

nspace = 3

veclen = 1

data = integer

field = irregular

14

Field file for bottle (continued)

coord 1 file=bottle.dat filetype=ascii skip=0 offset=0 stride=4

coord 2 file=bottle.dat filetype=ascii skip=0 offset=1 stride=4

coord 3 file=bottle.dat filetype=ascii skip=0 offset=2 stride=4

variable 1 file=bottle.dat filetype=ascii skip=0 offset=3 stride=4

15

16

3D axis with text title

Bottle

17

Used crop to reduce

the number of horizontal

steps drawn

Crop

18

Used crop to reduce

the number

of vertical points drawn

Crop

19

Used downsize to reduce

the number of steps drawn around

the circle

Downsize

20

Used downsize to reduce

the number

of profile points drawn

Downsize

21

22

Field file for 3D solid example

# AVS field file

ndim = 2

dim1 = 9

dim2 = 11

nspace = 3

veclen = 1

data = integer

field = irregular

23

Field file (continued)

coord 1 file=xmastree.dat filetype= ascii Skip=0 offset=0 stride=4

coord 2 file=xmastree.dat filetype= ascii Skip=0 offset=1 stride=4

coord 3 file=xmastree.dat filetype= ascii Skip=0 offset=2 stride=4

variable 1 file=xmastree.dat filetype=ascii Skip=0 offset=3 stride=4

24

25

Neither downsize nor crop used on the first image

26

Used downsize to reduce

the number of steps in each circle

Downsize

27

Used downsize to reduce

the number

of profile points

Downsize

28

Used crop to reduce

the number of horizontal

steps drawn

Crop

29

Here is a selection of some

other shapes created

by the students

30

“Brolly”

31

“Rings”

32

“Speaker”

33

Cross section of

a “speaker”

34

Two stroke

cylinder

35

Animation using AVS/Express

• Once an image has been created, the students can animate the image using the keyframe method of animation

• This creates a series of views (keyframes)

• AVS/Express can save images from a view

• Then add frames between the keyframes to produce the animated sequence

36

Key-frame animation

• Need two images which depict the start and end frames

• Create an animation sequence by adding frames between the two images

• The two images must have a reasonable level of coherence

37

AVS/Express

• AVS/Express interpolates images between a series of captured visualisations

• Student captures the keyframes

• Assigns each keyframe to a time step

• AVS/Express automatically adds the required number of frames between these keyframes to produce an animated sequence

38

Keyframes and interpolated frames

keyframes the user defines

interpolated frames added by AVS/Express

39

AVS animation features

• Simple to add/delete/move keyframes

• If not a regular time interval between keyframes, then specify the time of next frame before adding it

• Can create a cyclic animation

• Playback control offers forwards, backwards, and “bounce”

40

41

Keyframe Controls

42

Module Panel

Modules pull-down

menu

Playback the

animation

43

Finally . . .

Create 2D

profile

Create 3D data

Use AVS/Express

to animate the image

Use AVS/Express to visualise

the data

• This is how we teach visualisation in a level 2 module: -

• What could we do in the level 3 module?