3D computer graphics are works created by computers and specialized 3D software. In general, the art of 3D modelling is akin to photography, while the art of 2D graphics is analogous to painting. 3D computer graphics relies on the same algorithms that 2D computer graphics does. In computer graphics software this distinction is occasionally blurred. Some 2D applications use 3D techniques to achieve certain effects, e.g., lighting, while some primarily 3D applications make use of 2D visual techniques, i.e., 2D graphics is a subset of 3D graphics.
OpenGL and Direct 3D are two popular APIs for the generation of real-time imagery. Many modern graphics cards provide hardware acceleration based on the APIs that frequently enable to display complex 3D graphics in real-time. However, it is unnecessary to employ any of them to create 3D computer graphics. The process of creating 3D computer graphics can be divided into three basic stages, such as: modelling, scene layout setup and rendering.
The modelling stage can be described as shaping individual objects later used in the scene. There exist a number of modelling techniques, for instance, constructive solid geometry, NURBS modelling, polygonal modelling, subdivision surfaces and implicit surfaces. Modelling may also include editing object surface or material properties (e.g., colour, luminosity, reflection characteristics, transparency or index of refraction), adding textures and others. It may also include various activities related to preparing for animation of a 3D model. Modelling can be performed by means of dedicated programs (e.g., Lightwave Modeller, Rhinoceros 3D, Moray), application components (Shaper, Lofter in 3D Studio) or a scene description language.
Scene layout setup involves arranging virtual objects, lights, cameras and other entities on a scene which will be later used to produce an image or an animation. If it is used for animation, this stage usually makes use of a technique called key framing. This technique facilitates creation of complicated movements in the scene. Lighting is an important aspect of stage setup. Its effects can contribute greatly to the mood and emotional response, facts which are well-known to photographers and theatre lighting technicians.
Rendering is the final stage of creating the actual 2D image or animation from the prepared scene. Rendering for interactive media, such as, games and simulation, is calculated and displayed in real time, at rates of approximately 20 to 120 frames per second. Animations for non-interactive media, such as, video and film, are rendered much more slowly. For complex scenes rendering time of individual frames may vary from few seconds to an hour or more. Rendered frames are stored on a hard disk and then transferred to other media, such as, motion picture film or optical disk. These frames can be displayed at high frame rates, typically 24, 25 or 30 frames per second, to achieve the illusion of motion. Rendering software may simulate such visual effects as lens flares, depth of field or motion blur.
|
|
|
These are attempts to simulate visual phenomena resulting from the optical characteristics of cameras and human eye. These effects can lend an element of realism to a scene, even if the effect is merely a simulated artefact of a camera.
Techniques have been developed in order to simulate other naturally-occurring effects, for instance, the interaction of light with various forms of matter. Examples of such techniques include particle systems (which can simulate rain, smoke or fire), volumetric sampling (to simulate fog, dust and other spatial atmospheric effects) and a lot of others. Rendering is computationally expensive. Software for rendering is included in 3D software packages, but there are some rendering systems that are used as plug-ins to popular 3D applications.
The output of the rendering software is often used as only one small part of a completed motion-picture scene. Many layers of material may be rendered separately and integrated into the final stage by using special software packages.
NURBS stands for and is a mathematical model commonly used in computer graphics for generating and representing curves and surfaces. The development of NURBS (actually the Bezier Curve) began in the 1950s by engineers who needed free form surfaces representation like those that used for car bodies and ship hulls. Prior representations of this kind of surfaces existed only as a single physical model created by the designer.
NURBS is important for computer-aided design, manufacturing, engineering (CAD, CAM, CAE) and is a standard for numerous industries. But there is still a lot of confusion about their advantages and disadvantages for interactive modelling. In general, it is known that editing NURBS curves and surfaces is highly intuitive and predictable. Depending on the type of user interface, editing can be realized via NURBS control points, most obvious and common for Bezier curves, or via higher level tools, such as, spline modelling or hierarchical editing. Higher level tools can be designed to be very powerful and benefit from the ability of NURBS to create and establish continuity of different levels.
Task 8. Decide whether the following statements are true or false. It they are false, correct them.
1. All 2D applications use 3D techniques to achieve certain effects.
2. The output of the rendering software is seldom used as only one small part of a completed motion picture scene.
3. Real-time, interactive rendering of NURBS curves and surfaces were first made available in 1989.
4. Polygon representations are not used in all rendering techniques.
5. The first interactive NURBS modeling software for PCs was called CAS.
Task 9. Look in the text and find synonyms to the following:
operate, information, often, similar, method, different, too, famous, stage, result, several, to be able to.
Task 10. Arrange the words in the correct order to make sentences:
1. image, in, means, occurs, Real-time, generation, on-the-fly, that, or, real-time.
2. in, representation, geometric, stored, the, A, computer, three-dimensional, of, is, data.
3. starts, model, The, process, a, 3D, cel-shading, typical, with.
4. is, occurs, a, The, drawn, difference, cel-shaded, on-screen, when, object.
|
|
|
5. significant, factor, is, contributing, a, Lighting.
Task 11. Define the following terms:
graphics, algorithm, model, real-time, frame, simulation, technique, package, interactive, data.
Task 12. What do the following abbreviations stand for?
3D, API, NURBS, CAD, CAM, CAE, PC.
Task 13. Discuss the following questions:
1. What is 3D computer graphics?
2. In what cases do 2D applications use 3D techniques?
3. What are the stages of creating 3D computer graphics?
4. What do you know about modeling techniques?
5. What special programs can be used for modeling?
6. Who created NURBS?
7. When did NURBS appear?
8. What are the spheres of NURBS application?
