Object Representation

Object representation refers to the methods used to
describe the shape, structure, and appearance of
graphical objects in computer graphics systems.

1. Introduction

In computer graphics, objects must be represented in a form that allows them to be stored, manipulated, and displayed efficiently. Different representation methods are used depending on application needs.

Defines shape and structure of objects
Essential for rendering and modeling

2. Types of Object Representation

Wireframe Representation
Surface Representation
Solid Representation

3. Wireframe Representation

Wireframe representation describes an object using only its edges and vertices. It shows the skeletal outline of the object.

Simple and memory efficient
Does not represent surfaces

4. Surface Representation

Surface representation defines an object using its outer surfaces or faces. It provides more detail than wireframe models.

Uses polygon meshes
Represents visible surfaces

5. Solid Representation

Solid representation describes objects with complete volume information, including interior and exterior.

Most accurate representation
Used in CAD and simulation

6. Boundary Representation (B-Rep)

B-Rep represents a solid object by defining its boundary surfaces, edges, and vertices.

Defines faces, edges, and vertices
Widely used in CAD systems

7. Constructive Solid Geometry (CSG)

CSG represents objects by combining simple geometric primitives using Boolean operations.

Union, Intersection, Difference
Hierarchical representation

8. Comparison of Representations

Wireframe        Surface           Solid
--------------- ----------------- -------------------
Edges only       Outer surfaces    Complete volume
Fast rendering   Better realism    Accurate modeling
Less memory      Medium memory     High memory

9. Advantages

Flexible modeling approaches
Supports different applications
Efficient rendering control

10. Applications

3D modeling and animation
CAD/CAM systems
Scientific visualization

Practice Questions

What is object representation?
Explain wireframe representation.
What is surface representation?
Define solid representation.
Differentiate B-Rep and CSG.

Practice Task

Explain with diagrams: ✔ Wireframe vs surface model ✔ B-Rep structure ✔ CSG operations

📘 Computer Graphics