What is "ray casting"

n. (context computer graphics English) The calculation of intersections between a ray and a surface.

Ray casting is the use of ray–surface intersection tests to solve a variety of problems in computer graphics and computational geometry. The term was first used in computer graphics in a 1982 paper by Scott Roth to describe a method for rendering constructive solid geometry models.

Ray casting can refer to a variety of problems and techniques:

• the general problem of determining the first object intersected by a ray,

• a technique for hidden surface removal based on finding the first intersection of a ray cast from the eye through each pixel of an image,
• a non-recursive ray tracing rendering algorithm that only casts primary rays, or
• a direct volume rendering method, also called volume ray casting, in which the ray is "pushed through" the object and the 3D scalar field of interest is sampled along the ray inside the object. No secondary rays are spawned in this method.

Although "ray casting" and "ray tracing" were often used interchangeably in early computer graphics literature, more recent usage tries to distinguish the two. The distinction is that ray casting is a rendering algorithm that never recursively traces secondary rays, whereas other ray tracing-based rendering algorithms may do so.