Week 10 - Ray Tracing, Path Tracing and Radiosity Flashcards
What is forward tracing?
Trace starting point is the light source
Trace paths of photons from the light source
What is backward tracing?
Tracing starting point is the eye point
Shoot out rays from eye position and trace backward
What type of tracing is ray tracing (proposed by Whitted in 1979) based on?
Backward tracing
What is a light ray also known as in ray tracing?
Shadow ray
What is a light ray for?
Direct diffuse reflection as a ray from the point to the light source
In light paths notation, what do these letters stand for?
L
E
D
S
L - light source
E - eye
D - diffuse reflection
S - specular reflection / refraction
What is the general regular expression for the variety of different light paths in ray tracing/path tracing using the LEDS notation?
L(D|S)*E
What is path tracing (Kajiya 1986)?
An extension of ray tracing. Uses multiple rays per fragment pixel instead of single ray. At each object, make a “smart” decision how to continue tracing
What are the similarities between ray tracing and path tracing?
Both use backward tracing
Both are view-dependent algorithms
What does BRDF stand for?
Bidirectional Reflectance Distribution Functions
What is the general regular expression for the variety of different light paths in radiosity using the LEDS notation?
LD*E
How does the radiosity theory work?
No recursion required, focuses on object interactions
Splits scene into patches
Formulates problem as conservation of energy
Requires RGB wavelengths
What is the patching process?
Divide graphics scene into patches for computing radiosity
For small polygons, use the polygon map
For large polygons, they need to be subdivided
Since the emitted light will not be a constant across a large polygon we will need to see the subdivisions
The form factors couple every pair of patches, determining the proportion of radiated energy from one that strikes the other
What is radiosity?
Energy per unit area leaving a patch per unit time
What is the hemicube method?
Direct computation of the approximate form factor equation will be expensive to compute, so an approximate computation method (the hemicube) was developed
Using a bounding hemisphere it can be shown that all patches that project onto the same area of the hemisphere have the same form factor
What are 5 computation errors with radiosity and why are they errors?
Alias errors - computation of the form factors will involve alias errors
Form factor reciprocity - form factors have a reciprocal relationship thus form factors for only half the patches need be computed
Interpolation strategies - visual artefacts can occur with interpolation strategies but may not be significant for small patches
Meshing - meshing is the process of dividing the scene into patches, so artefacts are scene dependent, and errors can be caused by discontinuities in the radiosity function
Adaptive meshing - the idea of re-computing the mesh as part of the radiosity calculation, which tackles areas with strong discontinuities by putting more patches (elements) into that area, or moving the mesh boundary to coincide with the greatest change
