Parallel & Perspective Projections

Projection is the process of mapping 3D objects onto a
2D display surface. Parallel and perspective projections
are the two fundamental projection techniques used in
computer graphics.

1. Introduction

To display a three-dimensional scene on a two-dimensional screen, projection techniques are used. These techniques define how 3D points are transformed into 2D coordinates.

Converts 3D → 2D
Essential for rendering

2. Types of Projections

Parallel Projection
Perspective Projection

3. Parallel Projection

In parallel projection, projection lines are parallel to each other and do not converge at a single point. Object size remains constant regardless of distance.

No vanishing point
Preserves object dimensions

4. Types of Parallel Projection

Orthographic Projection
Oblique Projection

5. Orthographic Projection

Orthographic projection projects objects onto the view plane using perpendicular projection lines.

Used in engineering drawings
True dimensions preserved

6. Oblique Projection

In oblique projection, projection lines are not perpendicular to the view plane, allowing the front face to appear in true shape.

Cavalier projection
Cabinet projection

7. Perspective Projection

Perspective projection simulates human vision by making objects appear smaller as they move farther from the viewer. Projection lines converge at a vanishing point.

Realistic appearance
Uses vanishing points

8. Types of Perspective Projection

One-point perspective
Two-point perspective
Three-point perspective

9. Parallel vs Perspective Projection

Parallel Projection         Perspective Projection
-------------------------  ----------------------------
Parallel projection lines  Converging projection lines
No size reduction          Size reduces with distance
Less realistic             More realistic
Used in CAD                Used in games & movies

10. Applications

CAD and engineering drawings
3D modeling
Games and animation

Practice Questions

What is projection in computer graphics?
Explain parallel projection.
Differentiate orthographic and oblique projection.
What is perspective projection?
Compare parallel and perspective projection.

Practice Task

Explain with diagrams: ✔ Orthographic projection ✔ Perspective projection with vanishing point ✔ Parallel vs perspective comparison

📘 Computer Graphics