IPU BCA Semester 5: Computer Graphics - Perspective Projections vs Parallel Projections

Perspective Projections vs Parallel Projections

Computer Graphics

Question: How parallel projections are different from perspective projections? Explain by giving a suitable example.


Answer:

-	Parallel Projection	Perspective Projection
1.	In this projection, third z - co-ordinate is removed (3D to 2D) and parallel lines from vertex on the object are extended until they intersect the viewing plane.	Here projections are not parallel and they converge at a point (center or projection).
2.	Center of projection infinitely far from view plane like seeing through a telescope.	Center of projection finitely far from view plane
3.	Projectors will be parallel to each other (orthogonal)	Projectors will not be parallel to each other
4.	It requires the direction of projection (vector) be defined.	It requires first to define the location of the center of projection (point).
5.	Primarily, it is sub-divided into two types. orthographic - direction of projection is normal to view plane oblique - direction of projection not normal to view plane. There are other sub-types like Cavalier projection and Cabinet projection	It is classified into 1, 2, or 3-point perspective
6.	Suitable for drafting / CAD applications	It is more visually realistic and it has perspective foreshortening (objects further away appear smaller i.e. relative proportions are not preserved.)

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