17 - Ray Tracing and Path Tracing

Question 1

Light Path Notation

Answer 1

• L – Light source
• E – Eye
• D – Diffuse reflection
• S – Specular reflection/refraction
  And the normal notation:
• • • many allowed
• | - one allowed
• () - all elements contained within brackets (typically used to show that a pattern may be repeated)

Question 2

Ray Tracing

Answer 2

trace the path of light rays from the light source(s) in a scene as they interact with objects and surfaces, and to calculate how the light is reflected, refracted, or absorbed at each point in the scene.

-Forward
-Backward

Question 3

Forward

Answer 3

casting rays from the light source and tracing their path to the camera

inefficient as many rays doe not hit the camera

Question 4

Backward

Answer 4

where the eye is treated as the starting point, casting rays from the camera view and tracing their path back to the light source

more computationally efficient and dependednt on screen resolution

Question 5

Whitted Ray Tracing

Answer 5

method of ray tracing based on backward ray tracing.

considers three types of light interactions – refraction, perfect specular and (direct) diffuse.

Note that imperfect specular is NOT considered in this model.

One ray per pixel is “shot” from the eye position. When the ray “hits” an object, the light interactions are considered

only consider the ray that goes directly from the point to the light source.

If the object’s surface is shiny in some way (e.g. a mirror or some water), the interaction will be perfect specular, or refraction.

If the surface is matt (e.g. a wall), then the diffuse reflection is most likely considered.

Question 6

Whitted ray tracing and Shadows

Answer 6

Whitted ray tracing doesn’t consider diffuse reflection except at the light source.

This limitation of the model means that scenes rendered this way typically have very crisp and hard edges on shadows (since light is considered or it is not – there is no in between).

Question 7

Path Tracing

Answer 7

is an extension of ray tracing.

instead of just using one ray per fragment pixel, multiple rays are shot out. At each object, a decision is made about how to continue tracing.

Overall, as more paths are modelled, the end result is better.

Path tracing also uses backward tracing and is view-dependent

Question 8

What is the global illumination model?

Answer 8

Global illumination calculates lighting using direct and indirect lighting from the entire scene.

It calculates lighting by following every possible ray of light

It is very computationally expensive

Question 9

how is path tracing different from ray tracing ?

Answer 9

you shoot multiple rays per fragment

path tracing uses a random walk