Why is projection needed?

Display devices and paper are 2D, so 3D objects must be converted to a 2D view

To make objects smaller in memory

To remove hidden lines automatically

Which pair correctly describes projectors?

Parallel: projectors parallel; perspective: projectors meet at the COP

Parallel: projectors meet at a point; perspective: projectors parallel

Both have projectors meeting at a point

Oblique projection differs from orthographic in that:

Its projectors make an angle other than 90° with the plane

Its projectors are perpendicular to the plane

It has the COP at a finite distance

One-, two- and three-point perspective are classified by:

The number of objects in the scene

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Types of projections

Short answer

Projections map 3D objects to 2D. Parallel projections (orthographic—multiview, axonometric; oblique—cavalier, cabinet) preserve parallelism and scale. Perspective projections (one-, two-, three-point) use converging projectors for realistic foreshortening, but lose parallelism and distances.

Briefly explain various types of projections (significance of projection and its types).

Projection converts 3D objects into a 2D view on a view plane. It is needed because display devices and paper are two-dimensional. A projection is defined by projectors (lines from each point of the object) and a projection plane.

Projection
 |-- Parallel (projectors are parallel)
 |     |-- Orthographic (projectors perpendicular to plane)
 |     |     |-- Multiview (front, top, side)
 |     |     |-- Axonometric (isometric, dimetric, trimetric)
 |     |-- Oblique (cavalier, cabinet)
 |
 |-- Perspective (projectors meet at a point, COP)
       |-- One-point, two-point, three-point

1. Parallel projection: projectors are parallel, so the centre of projection is at infinity. Parallel lines stay parallel and relative dimensions are kept, so it is used in engineering drawing.

Orthographic: projectors are perpendicular to the view plane. Front, top and side views show true shape of one face. Axonometric views (isometric, dimetric, trimetric) rotate the object so that several faces are visible.
Oblique: projectors make an angle other than 90° with the plane. Faces parallel to the plane keep true shape. Types are cavalier (receding lines at full length) and cabinet (half length).

2. Perspective projection: projectors converge at the centre of projection. Distant objects look smaller, so the view looks realistic, but parallel lines (not parallel to the view plane) meet at vanishing points and distances are not preserved. Types depend on the number of principal vanishing points: one-point, two-point and three-point.

Point	Parallel	Perspective
Projectors	Parallel	Meet at COP
Size with distance	Constant	Smaller when farther
Realism	Less	More
Measurement	Preserved	Not preserved
Use	CAD, drawings	Games, animation, architecture

✓ Answer checked by Claude Opus 5.5 (high effort)

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