Three-Dimensional Concepts

Chapter 9

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.

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.

Coordinate Reference This coordinate reference defines the position and

orientation for the plane of the camera film.

Three-Dimensional Coordinates

x

y

z

x

y

z

Right handed Left handed

Shading left-handed

Shading right-handed

Wireframe

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.

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

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.

It has two major characteristics– Smaller as their distance from the observer

increases.– Foreshortened: the size of an object’s

dimension along the line of sight are relatively shorter than dimensions across the line of sight.

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

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.

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.

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

Three-Dimensional Display Methods

• Surface rendering

• Set the surface intensity of objects according to

• Lighting conditions in the scene

• Assigned surface characteristics

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.

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

Three-Dimensional Display Methods

• Cutaway view

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

Three-dimensional and stereoscopic views