Radiosity - Week 7

Question 1

How does radiosity treat light?

Answer 1

As though it’s energy being exchanged between areas of the scene

Question 2

What does radiosity support? What is more tricky?

Answer 2

diffuse inter-reflection, subtle lightling, colour bleed and nice soft shadows happen naturally.

Transparency and specular reflection are, whilst not impossible, considerably more tricky.

Question 3

What is the Cornell box?

Answer 3

A box that was photographed and re-created as a rendering. The photo can be used as a reference image for an rendering technique that focuses on diffuse interreflection.

Question 4

What is colour bleed?

Answer 4

Colour picked up from light scattered off of nearby objects

Question 5

What effects come from diffuse interreflection?

Answer 5

Colour bleed
Soft shadows

Question 6

What are light sources in a radiosity solver?

Answer 6

Polygons in the scene that happen to be emitting their own light energy.

They are an area light source, rather than a point light source

Question 7

What were radiosity methods first developed for?

Answer 7

Modelling heat transfer

Question 8

What is radiance? (Also what is flux in this context)

Answer 8

Thermodynamic radiosity - the flux leaving a surface at point x (irradiance is the flux arriving at that point)

flux - a flow of particles (in our case they are photons)

Question 9

For a scene with n discrete patches, how many simultaneous equations need to be solved by a radiosity solver?

Answer 9

n

Question 10

What techniques can be used to solve simultaneous equations from the radiosity equation?

Answer 10

Jacobi iteration or the Gauss–Seidel method (hugely computationally intensive, can’t be done in real time)

Question 11

What can radiosity not compute (as it doesn’t take in the viewpoint)

Answer 11

There’s no specular or mirrored effects

Question 12

Why does it not really matter how long radiosity solving takes for a scene?

Answer 12

The algorithm is object space, so the calculation only needs to be done once.

Question 13

What factors influence the visibility of one patch to another in radiosity?

Answer 13

• The size of the patches, a bigger patch emits more energy
• The distance between the patches, electromagnetic energy (like light) attenuates according to the inverse square of the distance between source and destination (irradiance is also inversely proportional to the inverse of the same distance squared, so a small increase in distance has quite a big effect)
• The orientation of two patches to one another, if they don’t face one another there’s no meaningful exchange of energy, maximum when they face head onto one another
• If there is something in the way / occludes the transfer. It could block all of it or just some of it

Question 14

What is progressive / shooting radiosity?

Answer 14

Iteratively choosing the patches with the most light to emit and looking at their effect on other patches.

Question 14

What is progressive / shooting radiosity?

Answer 14

Iteratively choosing the patches with the most light to emit and looking at their effect on other patches.