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3D Concepts

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Three-dimensional Graphics

3D computer graphics involves the additionaldimension of depth, allowing us to make morerealistic and higher fidelity representations of 3Dobjects in the real world

Paradoxically in most cases this is stillrepresented in 2D output devices utilisingtechniques to render these objects with theillusion of depth

3D Graphics is characterised more by the 3Dnature of the Models (input into rendering) ratherthan the final display (output) modeling world

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3D Coordinate Systems

We add a third dimension to our real-world ormodeling coordinate system by adding a z-axis toour 2D system

There are two possible ways of attaching the Z-axis

This gives rise to a left-handed or a right-handedsystem.

Imagine that the thumb and finger of each hand isthe x and y axis resp. The direction of your middlefinger shows the direction of the z-axis in eachsystem

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x

y

z

x

y

z

Left Handed Right Handed

(1,-1,1)(1,-1,-1)

The Right-handed system is the most commonly used.

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Object Representation

Graphics scenes can contain manydifferent kinds of objects and materialsurfaces

Trees, flowers, clouds, rocks, water, bricks,wood paneling, rubber, paper, marble, steel,glass, plastic and cloth

So it may not be surprising that there isno single method that we can use todescribe all the characteristics of these

different shapes/materials

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Object Representation

Scene = an assembly of one or moremodels

A model contains

Structural description: Geometry of the

shapeSurface description: Appearance and

light

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3D Object Representation

Object Boundaries:

Plane,

Curved Surfaces

Object Interiors:

Solid Objects:

Boundary RepresentationSpace-partition Representation

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3D Object Representations

Boundary representation

A set of surfaces that separate the objectinterior from the environment

Eg) Polyhedra, curved boundary surfaces

Space-partitioning

Partitioning the spatial region into a set ofsmall, nonoverlapping, contiguous solids(usually cubes)

Eg) Volumetric data, octrees, BSP trees

Procedural methods

Fractals, shape grammars

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3D Object Representation

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