# Three-Dimensional Concepts - PowerPoint PPT Presentation

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## Three-Dimensional Concepts

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### Chapter 9 Three-Dimensional Concepts Three Dimensional Graphics It is the field of computer graphics that deals with generating and displaying three dimensional ... – PowerPoint PPT presentation

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Title: Three-Dimensional Concepts

1
Three-Dimensional Concepts
• Chapter 9

2
Three Dimensional Graphics
• It is the field of computer graphics that deals
with generating and displaying three dimensional
objects in a two-dimensional space(eg display
screen)
• In addition to color and brightness, a 3-D pixels
adds a depth property that indicates where the
point lies on the imaginary z-axis.

3
• When many 3-D pixels are combined, each with its
own depth value, the result is a 3-D surface
called a texture.
• Objects are created on a 3-D stage where the
current view is derived from the camera and light
sources, similar to the real world.

4
Coordinate Reference
• This coordinate reference defines the position
and orientation for the plane of the camera film.

5
Three-Dimensional Coordinates
Right handed
Left handed
y
y
z
x
x
z
6
7
8
Wireframe
9
Three-Dimensional Display Methods
• Parallel projection
• Project points on the object surface along
parallel lines onto the display plane.
• Parallel lines are still parallel after
projection.
• Used in engineering and architectural drawings.

10
• By selecting different viewing positions, we can
project visible points on the object onto the
display plane to obtain different two-dimensional
views of the object.

Top View
Side View
Front View
11
Three-Dimensional Display Methods
• Perspective projection
• Project points to the display plane along
converging paths.
• This is the way that our eyes and a camera lens
form images and so the displays are more
realistic.

12
• It has two major characteristics
• Smaller as their distance from the observer
increases.
• Foreshortened the size of an objects dimension
along the line of sight are relatively shorter
than dimensions across the line of sight.

13
Three-Dimensional Display Methods
• Depth cueing
• Identify which is the front and which is the back
of displayed objects
• For wireframe displays
• Vary the intensity of objects according to their
distance from viewing position
• For the atomsphere

14
Three-Dimensional Display Methods
• Depth Cueing
• To easily identify the front and back of display
objects.
• Depth information can be included using various
methods.
• A simple method to vary the intensity of objects
according to their distance from the viewing
position. Eg lines closest to the viewing
position are displayed with the highest
intensities and lines farther away are displayed
with decreasing intensities.

15
• Application is modeling the effect of the
atmosphere on the pixel intensity of objects.
More distant objects appear dimmer to us than
nearer objects due to light scattering by dust
particles, smoke etc.

16
Three-Dimensional Display Methods
• Visible line and surface identification
• Highlight the visible lines or display them in
different color
• Display nonvisible lines as dashed lines
• Remove the nonvisible lines

17
Three-Dimensional Display Methods
• Surface rendering
• Set the surface intensity of objects according to
• Lighting conditions in the scene
• Assigned surface characteristics

18
• Lighting specifications include the intensity and
positions of light sources and the general
background illumination required for a scene.
• Surface properties include degree of transparency
and how rough or smooth the surfaces are to be.

19
Three-Dimensional Display Methods
• Exploded and Cutaway Views
• To maintain a hierarchical structures to include
internal details.
• These views show the internal structure and
relationships of the object parts

20
Three-Dimensional Display Methods
• Cutaway view
• Remove part of the visible surfaces to show
internal structure.

21
Three-dimensional and stereoscopic views