# Computer Graphics Questions & Answers – Parallel Projections

This set of Computer Graphics Multiple Choice Questions & Answers (MCQs) focuses on “Parallel Projections”.

1. The planar geometric projections can be divided into how many categories?
a) 2
b) 3
c) 4
d) 5

Explanation: The planar projections can be divided into 2 broad categories. These are Parallel Projection and Perspective Projection.

2. The Parallel Projection can be divided into how many categories?
a) 6
b) 8
c) 2
d) 5

Explanation: Parallel Projection can be mainly divided into two parts – Orthographic Projection and Oblique Projection. Orthographic projection can be further divided into – Top, Front, Side and Axonometric. Oblique Projection can be further divided into – Cavalier and Cabinet.

3. Which types of lines are used to transform coordinate points to the view plane in parallel projection?
a) Intersecting Lines
b) Parallel Lines
c) Perpendicular Lines
d) Bisecting Lines

Explanation: Coordinate position are transformed to the view plane along parallel lines. A parallel projection preserves relative proportion of objects, but does not give us a realistic representation of the object.

4. Which type of parallel projection has projection vectors perpendicular to the viewing plane?
a) Axonometric Projection
b) Orthographic Projection
c) Oblique Projection
d) Perspective Projection

Explanation: In orthographic projection, the projection vectors are perpendicular to the viewing plane. Orthographic projection is used to produce the front, side, and top views of an object.

5. Which type of parallel projection has projection vectors not perpendicular to the viewing plane?
a) Oblique Projection
b) Perspective Projection
c) Axonometric Projection
d) Cabinet Projection

Explanation: In oblique projection, the projection vectors are not perpendicular to the viewing plane. Angles and lengths are preserved for faces parallel the plane of projection.  Preserves 3D nature of an object
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6. Which of the following orthographic parallel projection is called as a plan view?
a) Front
b) Side
c) Rear
d) Top

Explanation: Top orthographic projection is called as plan view. Front, rear and side orthographic projections of an object are called as the elevations.

7. The Axonometric parallel projection can be divided into how many sub categories?
a) 2
b) 3
c) 4
d) 5

Explanation: The Axonometric parallel projection can be divided into 3 main subcategories. These are – Isometric parallel projection, Dimetric parallel projection and trimetric parallel projection.

8. Oblique parallel projection preserves the 3 D nature of the object.
a) True
b) False

Explanation: In oblique parallel projection the 3 D nature of the object remains preserved. The angles, distances and the parallel lines in the plane are projected accurately. In oblique projection, projections are not perpendicular to the viewing plane.

9. In cabinet projection, what is the projected length of the lines that are perpendicular to the viewing plane?
a) Same length as the original
b) Double the length of the original
c) Half the length of the original
d) Projected length does not depend on the original length

Explanation: In cabinet projection, the projected length of the lines that are perpendicular to the viewing plane is half the length of the original. It gives a more realistic view of the object than the cavalier projection.

10. Which of the following is the correct set of equations for oblique parallel projection?
a) xp = x + z (L1 + cosθ)
yp = y + z (L1 + sinθ)
b) xp = x + z(L1sinθ)
yp = y + z(L1cosθ)
c) xp = x – z(L1cosθ)
yp = y – z(L1sinθ)
d) xp = x + z(L1cosθ)
yp = y + z(L1sinθ)

Explanation: The set of equations that is correct for oblique parallel projection is –
xp = x + z(L1cosθ)
yp = y + z(L1sinθ)
where, xp and yp are projected coordinates. (x, y, z) are the original coordinates. L1 is the length between the object and the view plane and θ is the angle with the horizontal direction of the projection plane.

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