Beam tracing
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. In beam tracing, a square beam is initially sent 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.
Beam tracing solves certain problems related to sampling and aliasing, which can plague conventional ray tracing. However, the additional programming 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.
Beam tracing is related to cone tracing.