Spatial Partitioning in Ray Tracing, Introduction to Radiometrics

I have been in touch with Sicha tree before, and KD-tree and BSP-Tree are used here

• KD-Tree
  
• For how to divide:

1. First, you need to know which axis to divide along.
2. Divided location
3. All nodes do not exist on the parent node, only exist on the leaf node

• For how to find
  the ray passing through the bounding box A, then intersect its two child nodes respectively
• If there is an intersection point with the child node as well as leaf node 1, then directly calculate all objects of the leaf node separately
• If there is an intersection with child node B, because it is not a leaf node, then calculate and search for its child nodes 2 and C respectively
• reciprocating in turn
  
• BVH structure
  This structure is not divided according to space, but according to objects. Divide
  objects into two piles, and re-find their bounding boxes
  . In this way, an object can only appear in one bounding box.
  
• Radiometrics
  It is a method that can accurately define various information of light. For example, the intensity of light has its physical meaning, and it is not a quantity that can be defined. The introduction of radiometrics can help us define various types of light more precisely.
  Introducing relevant new variables (Radiant Energy and Flux)
• Radiant energy Radiant energy (joules)
  
• Radiant flux Radiant flux (similar to physical work)
  
• intensity intensity (radiant flux/solid angle)
  
• Definition of solid angle
  Definition of angle in 2D space:
  
  Definition of solid angle in 3D space:
  
• irradiance irradiance (radiant flux density)