3D Display Methods - Mod -3

8/22/2019 3D Display Methods - Mod -3

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Three-DimensionalConcepts

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 andorientation for the plane of the camera film.


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Three-Dimensional Coordinates

x

y

z

x

y

z

Right handed Left handed


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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 afterprojection.

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 ViewFront View


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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 displayedobjects

For wireframe displays

Vary the intensity of objects according to their distance

from viewing position For the atomsphere


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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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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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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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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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Cutaway view

Remove part of the visible surfaces to show internalstructure.


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Three-dimensional and stereoscopic views

3D Display Methods - Mod -3

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