Projections

Question 1

What is an Orthographic Projection?

Answer 1

This is a Projection in which the

Projection Plane

is Parallel to one of the world planes

Question 2

Does Perspective Projection preserve Parallel lines?

Answer 2

No

Parallel Lines converge to a Vanishing Point

Question 3

How can we carry out an Orthogonal Projection?

Answer 3

Set all the Z values of the points to 0

This will map points to the Z=0 planes

Question 4

What is an Axonometric Projection?

Answer 4

This is where the Projection Plane is at 45 degrees to the world axis,

It is symmetrical to one or more of the axis

Question 5

What is the most general case of a Parallel Projection?

Answer 5

Oblique Projection

The Projection Plane can have any orientation

The Plane does not have to be perpendicular or anything, there are no constraints

Question 6

In a Perspective Projection, do objects further away appear closer together?

Answer 6

Yes

Question 7

Where should a point in 3D Space be drawn in a Perspective Projection?

Answer 7

If we draw a straight line between the “Eye” and the point, we would draw the point where it intersects the Projection Plane

Question 8

What is a 1-Point Perspective?

Answer 8

This is where there is only a single Vanishing Point

Question 9

What is a 2-Point Perspective?

Answer 9

If we take a set of Parallel Lines and extend them we will get 2 Vanishing Points

Question 10

What is a 3-Point Perspective?

Answer 10

If we take a set of Parallel Lines and extend them we will get 3 Vanishing Points

Question 11

What does the View Volume look like in a Parallel Projection?

Answer 11

We have a near-Plane (the Projection Plane), which is the near plane

and a far plane,

The view Volume is a cuboid shape

Question 12

What does the View Volume look like in a Perspective Projection?

Answer 12

The near and far plane are parallel

The view volume forms a Frsutum

Question 13

How would we define the View Volume for a Parallel Projection?

Answer 13

We need to give the distances of the near and far planes

And give the left,right,top and bottom of these planes

Question 14

How would we define the View Volume for a Perspective Projection?

Answer 14

We need to give the distances of the near and far planes

We need to give the angle of the field of view

and an aspect ratio, this represent the ratio between the width and height of the Frustum

Question 15

Doing a Perspective Projection gets rid of the Z-Values which could be used later?

How can we perform a Perspective Projection, and keep the Z-Values?

Answer 15

Projection Normalisation

Transform the Frustum into a Cube

and then perform an Orthographic Projection

This process is equivalent to the original Perspective Projection

and the Z-Values are not lost

Question 16

What does Clipping do?

Answer 16

It removes the parts of objects that are not in the View Volume