Lernkartei Interaktive Computergrafik (Seite 3 von 5)

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Erstellt / Aktualisiert	24.04.2021 / 21.07.2021
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How are vectors represented?

as scalar

as n-tupels

as a field K

How do you calculate the length of a vector v ?

sqrt(v*v)

Summe i=0 bis i=n-1 vi

sqrt(Summe i00 bis i=n-1 vi*vi)

How long is the vector resulting from a cross product?

1

Equal to the sine of the angle between the operands.

Equal to the area of the parallelogram defined by the operands.

Equal to the length of the longer operand.

Which vector results from a+d

b

c

e

f

g

Which vector results form a-d

b

e

f

g

h

What is the length of vector (2 1 0)?

2

sqrt(2)

5

sqrt(3)

sqrt(5)

A vector is defined by?

amplitude and phase

altitude and elevation

magnitude and direction

attitude and length

What is shading?

The attribution of a color value to a point of a pixel of the screen

Running a shader on the graphics card.

The result of a ray intersection with objects for ray tracers

Which are interpretations of light?

wave

hypercube

double helix

particle

How is the light vector l defined?

As the perpendicular to the light direction

As the opposite to the light direction.

As the normalized light direction.

What is Radiance?

The irradiance over the surface of a sensor

The density of light flow per area and incoming direction

The light-proof enclosure to restrict directions of light

Which relationships describe the contribution of light rays hit an object for the irradiance?

The flatter the angle of irradiance, the higher the contribution to the incident radiation.

The steeper the angle of irradiance, the higher the contribution to the incident radiation

Negative angles / angles greater than pi/2 of irradiance are not possible

The total irradiation is the sum of all light passing through a unit area per second.

Different light models are used to explain different light behavior. Match the behaviors to the models that best describe them.

models: Quantum theory, special relativity, wave optics, geometrical optics:

emission, absorption, reflection, refraction, interference, dispersion, diffraction, time dilatation, redshift, blueshift, aberration

Quantum theory: emission, absorption

special relativity: time dilatation, redshift, blueshift, aberration

wave optics: interference, dispersion, diffraction

geometrical optics: reflection, refraction

What is equivalent to the irradiance?

The cosine of the light’s incidence angle arriving at the surface.

The coefficient of randomness describing light directions the surface is lit from.

The sum of energies of photons passing through the surface in one second

How is the smoothness parameter in light simulations modified to account for increased scattering on the macro levels?

The smoothness parameter is increased.

The smoothness parameter is decreased

The smoothness parameter is kept constant.

Which scattering type interacts with the interior of an object?

refraction

transmission

reflection

The ambient lighting in the Phong Lighting Model…

depends on the surface normal.

yields the same reflected ambient energy for every object.

models direct light off of a light source.

simulates a global light contribution.

Given is a light source of radiance 0.5 that illuminates a surface of diffuse reflectivity coefficient 1. Calculate the reflected diffuse energy according to the Phong Lighting Model. The constellation is as shown in the image below.

sqrt(3)/4

sqrt(3)/2

1/2

1/4

Which values are needed in the formula of the Diffuse Phong Lighting calculation?

position of light source

surface normal

position of observer / camera

ambient material coefficient

Lambertian surfaces …

emit more radiant intensity the closer an observer approaches the surface

approximate metal surfaces for large diffuse material coefficients and low angles of the incident light and the surface normal.

are translucent.

show radiant intensity between the direction of the incident light and the surface normal

have the same apparent radiance from all viewing angles.

Given is a light source of radiance 0.5 that illuminates a surface of specular reflectivity coefficient 1. The surface’s specular shininess is 2. Calculate the reflected specular energy in the observed direction according to the Phong Lighting Model. The constellation is as shown in the image below.

3/4

3/8

1/4

1/8

An observer is holding a flash light next to the eye illuminating the ground in front of her. The ground is represented as a perfect plane. When looking at the horizon, which of the three part(s) of the Phong model do(es) (almost) not contribute?

ambient

specular

diffuse

Using a function yielding intensity values of each point on an object using Phong’s reflectance model is called

shading

lighting

lightning

diffusing

A sphere has a smaller, more pronounced specular highlight than an other sphere if…

the angle between the perfect reflection direction and the direction to the observer is smaller.

the shininess material coefficient is larger

then angle between the incident light direction and the surface normal is larger.

the specular material coefficient is smaller.

Ambient light directly simulates…

the sun

indirect lighting

direct light from artificial sources in the scene

Which postulation explains the direction of a refraction vector?

Snell’s law

Fresnel equation

Prism lemma

Plano-Convex Algorithm

What is the critical angle for refractions?

The largest angle of incidence resulting in refraction.

The smallest angle of reflection without refraction

The angle of an even energy split between refraction and reflection.

Assuming a unit vector l pointing from the surface to a light source and a surface normal n , which is the solution for the reflection vector r ?

r =2(n*l)n-l

r = 2(l*n)l-n

r =2(l*n)n-l

r=2(n*l)l-n

The Fresnel Equation …

calculates the magnitude of refraction.

calculates the direction of reflection.

results from Maxwell’s wave equation.

assumes elimination coefficient 1.

How do you calculate the magnitude of reflection?

|t|=(1-F)|i|

|t|=|i|-|i|F

|r|=F|i|

r=2(l*n)n-1

How do you calculate the magnitude of refraction?

r = 2(n*l)l-n

|t| = (1-F)|i|

|r|=F|i|

|t|=|i|-|i|F

What unit is used for radian flux?

J/s

J

m/s

Js

W

How many photons per joule are there for lambda=625?

3.27*10^18

2.87*10^18

3.15*10^18

2.77*10^18

Assign the symbols to the respective radiometric quantities!

radiant energy, raidant flux, exitance, radiant intensity, radiance, irradiance

theta, Q, E, L, M, I

radiant energy: Q

raidant flux: theta

irradiance: E

exitance: M

radiant intensity: I

radiance: L

What is a steradiant?

An intersection arc on a unit circle.

An intersection rectangle on a unit cube

An intersection patch on a unit sphere.

When is the point light approximation reasonable?

If the distance to the light is approximately the light’s width.

If the distance to the light is approximately 2 times the light’s width

If the distance to the light is approximately 5 times the light’s width

If the distance to the light is approximately 6 times the light’s width.

If the distance to the light is approximately 7 times the light’s width.

What is a BRDF?

A 4 DoF gantry to measure radiance

A function defining how light is reflected at opaque surfaces

A distribution.

A geometry for isotropic emission.

What are examples for BRDFs?

Phong reflection Model

Red-Green Comprehensive Model

Oren-Nayar Diffuse Microfacet BRDF

Cook-Torrance Specular Microfacet BRDF

Radiant flux analytic BRDF

What is the result of the following term?

(2 3 1 1)

(2 3 5 0)

(2 3 1 0)

What is the difference between a point and a vector?

A vector....:

..can describe a direction.

..can define a point if the vector is bound.

...can be bound or unbound.

A point...:

...is an pbject without a higher dimensional measure of values described by the intersection of two lines.

...is the intersection of two lines.

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