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Beam tracing is a derivative of the ray tracing algorithm that replaces rays, which have no thickness, with beams. Beams are shaped like unbounded pyramids, with (possibly complex) polygonal cross sections. Beam tracing was first proposed by Paul Heckbert and Pat Hanrahan^[1].

In beam tracing, a pyramidal beam is initially cast through the entire viewing frustum. This initial viewing beam is intersected with each polygon in the environment, from nearest to farthest. Each polygon that intersects with the beam must be visible, and is removed from the shape of the beam and added to a render queue. When a beam intersects with a reflective or refractive polygon, a new beam is created in a similar fashion to ray-tracing.

A variant of beam tracing casts a pyramidal beam through each pixel of the image plane. This is then split up into sub-beams based on its intersection with scene geometry. Reflection and transmission (refraction) rays are also replaced by beams. This sort of implementation is rarely used, as the geometric processes involved are much more complex and therefore expensive than simply casting more rays through the pixel.

Beam tracing solves certain problems related to sampling and aliasing, which can plague conventional ray tracing. However, the additional computational complexity that beams create has made them unpopular. In recent years, increases in computer speed have made Monte Carlo algorithms like distributed ray tracing much more viable than beam tracing.

However, beam tracing has had a renaissance in the field of acoustic modelling^[2], in which beams are used as an efficient way to track deep reflections from sound source to receiver (or vice-versa), a field where ray tracing is notoriously prone to sampling errors^[3].

Beam tracing is related in concept to cone tracing.

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