---
title: "Parallel versus oblique projection"
subject: "Computer Graphics"
chapter: 4
key: "semester_5/computer_graphics:parallel-vs-oblique-projection"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/parallel-vs-oblique-projection
site: BCT Engineering
---

# Parallel versus oblique projection

Computer Graphics · Chapter 4: Three-Dimensional Graphics

- Asked in: 2081 Chaitra (new course), 3 marks
- Video: [Projections in Computer Graphics| Perspective and Parallel Projections](https://www.youtube.com/watch?v=Njc5EhlzjEk) — Homelearners
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/parallel-vs-oblique-projection
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-4

## Question

Differentiate between parallel projection and oblique projection.

## Short answer

Parallel projection uses parallel projectors; oblique is a subtype where projectors are not perpendicular to the view plane. Orthographic projectors are perpendicular; oblique shows front face true shape and depth sides, with types like cavalier and cabinet.

## Answer

**Parallel projection** projects points along parallel lines (projectors) onto the view plane. **Oblique projection** is one kind of parallel projection in which the projectors are not perpendicular to the view plane. The other kind is orthographic, where projectors are perpendicular.

| Point | Parallel projection (general) | Oblique projection |
|---|---|---|
| Meaning | All projectors are parallel | Parallel projectors at an angle (not 90°) to the view plane |
| Includes | Orthographic and oblique | A subtype of parallel |
| Projector direction | Perpendicular (orthographic) or slanted | Always slanted |
| View of object | Orthographic shows one face per view, true shape | Shows front face in true shape plus depth sides together |
| Types | Multiview, axonometric (isometric etc.), oblique | Cavalier (α = 45°), cabinet (α = 63.4°) |
| Matrix | Orthographic: diag(1,1,0,1) | Third column has L1cosφ, L1sinφ |
| Use | Engineering drawings | Quick pictorial sketches |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Oblique projection is:
   A. A subtype of parallel projection with slanted projectors
   B. Same as perspective
   C. A subtype of perspective
   D. Unrelated to parallel
   Answer: A. Parallel includes orthographic and oblique. (Key point: Relation)

2. In orthographic projection the projectors are:
   A. At an angle to the plane
   B. Perpendicular to the view plane
   C. Converging at a point
   D. Not defined
   Answer: B. Orthographic is the perpendicular special case. (Key point: Projectors)

3. Cavalier and cabinet projections differ in:
   A. The COP
   B. Colour
   C. Receding line length (full vs half)
   D. The number of vanishing points
   Answer: C. Cavalier α = 45° keeps full length, cabinet α = 63.4° halves it. (Key point: Oblique types)

## Related in Computer Graphics

- [Derive oblique projection matrix](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aoblique-projection-matrix-derive) — Computer Graphics, chapter 4, asked 3×
- [Derive parallel projection matrix](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aparallel-projection-matrix-derive) — Computer Graphics, chapter 4, asked 2×

## Related in other subjects

- [Series versus parallel circuit comparison](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Aseries-parallel-comparison-table) — Basic Electrical Engineering, chapter 1
- [Head loss ratio, parallel versus series](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Aparallel-vs-series-head-loss-ratio) — Hydraulics, chapter 2