Three-Dimensional Concepts

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Three-Dimensional Concepts

• Chapter 9

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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.

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• 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.

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Coordinate Reference

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

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Three-Dimensional Coordinates
Right handed
Left handed
y
y
z
x
x
z
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Shading left-handed
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Shading right-handed
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Wireframe
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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.

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• 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
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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.

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• 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.

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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

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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.

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• 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.

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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

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Three-Dimensional Display Methods

• Surface rendering
• Set the surface intensity of objects according to
  
• Lighting conditions in the scene
• Assigned surface characteristics

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• 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.

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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

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Three-Dimensional Display Methods

• Cutaway view
• Remove part of the visible surfaces to show
  internal structure.

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Three-dimensional and stereoscopic views