Using AVSExpress in an Introductory Computer Graphics Course

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Using AVS/Express in an Introductory Computer
Graphics Course
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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

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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

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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

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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 Radiuscosine(?)
• Y Radiussine(?)
• where ? is the angle in radians between the X
  axis and a point on the circle (in an
  anti-clockwise direction)

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Draw a Circle
Y-axis

• ? degrees?/180
• X Radiuscosine(?)
• Y Radiussine(?)

Radius
?
X-axis
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Create 3D solid from 2D profile
Y
Y
Solid of revolution of bottle shape
Z
Profile
X
X
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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.

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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

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3D Surface

• Create a new mid-way point

• Make its height the average of the adjacent points

• Randomly modify its new height within limits

a
b
c
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Include the diagonals

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

a
b
c
d
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Field file for a bottle

• AVS field file
• bottle
• ndim 2
• dim1 21
• dim2 15
• nspace 3
• veclen 1
• data integer
• field irregular

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Field file for bottle (continued)

• coord 1 filebottle.dat filetypeascii skip0
  offset0 stride4
• coord 2 filebottle.dat filetypeascii skip0
  offset1 stride4
• coord 3 filebottle.dat filetypeascii skip0
  offset2 stride4
• variable 1 filebottle.dat filetypeascii skip0
  offset3 stride4

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Bottle
3D axis with text title
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Crop
Used crop to reduce the number of horizontal
steps drawn
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Crop
Used crop to reduce the number of vertical points
drawn
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Downsize
Used downsize to reduce the number of steps drawn
around the circle
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Downsize
Used downsize to reduce the number of profile
points drawn
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Field file for 3D solid example

• AVS field file
• ndim 2
• dim1 9
• dim2 11
• nspace 3
• veclen 1
• data integer
• field irregular

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Field file (continued)

• coord 1 filexmastree.dat filetype ascii Skip0
  offset0 stride4
• coord 2 filexmastree.dat filetype ascii Skip0
  offset1 stride4
• coord 3 filexmastree.dat filetype ascii Skip0
  offset2 stride4
• variable 1 filexmastree.dat filetypeascii
  Skip0 offset3 stride4

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Neither downsize nor crop used on the first image
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Downsize
Used downsize to reduce the number of steps in
each circle
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Downsize
Used downsize to reduce the number of profile
points
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Crop
Used crop to reduce the number of horizontal
steps drawn
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• Here is a selection of some
• other shapes created
• by the students

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Brolly
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Rings
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Speaker
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Cross section of a speaker
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Two stroke cylinder
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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

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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

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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

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Keyframes and interpolated frames
keyframes the user defines
interpolated frames added by AVS/Express
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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

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Keyframe Controls
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Module Panel
Modules pull-down menu
Playback the animation
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Finally . . .

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

Use AVS/Express to animate the image
Use AVS/Express to visualise the data
Create 2D profile
Create 3D data

• What could we do in the level 3 module?