Ray tracing (physics)

In physics, ray tracing is a method for calculating the path of waves or particles through a system with regions of varying propagation velocity, absorption characteristics, and reflecting surfaces.

For example, ray-marching involves repeatedly advancing idealized narrow beams called rays through the medium by discrete amounts.

Notable examples include Large Synoptic Survey Telescope where this kind of ray tracing was first used with PhoSim[2] to create simulated images.

This form of ray tracing involves the integration of differential equations that describe the propagation of electromagnetic waves through dispersive and anisotropic media such as the ionosphere.

Ray tracing may be used in the design of lenses and optical systems, such as in cameras, microscopes, telescopes, and binoculars, and its application in this field dates back to the 1900s.

The following effects can be integrated into a ray tracer in a straightforward fashion: For the application of lens design, two special cases of wave interference are important to account for.

The optical formulas of many classic photographic lenses were optimized by roomfuls of people, each of whom handled a small part of the large calculation.

The basic principles of the most frequently used algorithm could be found in Spencer and Murty's fundamental paper: "General ray tracing Procedure".

In seismology, geophysicists use ray tracing to aid in earthquake location and tomographic reconstruction of the Earth's interior.

Ray tracing may be used to compute paths through a geophysical model, following them back to their source, such as an earthquake, or deducing the properties of the intervening material.

[8] In particular, the discovery of the seismic shadow zone (illustrated at right) allowed scientists to deduce the presence of Earth's molten core.

In general relativity, where gravitational lensing can occur, the geodesics of the light rays receiving at the observer are integrated backwards in time until they hit the region of interest.

Analytic solutions for ray trajectories in simple plasma density profiles are a well established,[12] however researchers in laser-plasma physics often rely on ray-marching techniques due to the complexity of plasma density, temperature, and flow profiles which are often solved for using computational fluid dynamics simulations.

Ray tracing of a beam of light passing through a medium with changing refractive index . The ray is advanced by a small amount, and then the direction is re-calculated.
Radio signals traced from the transmitter at the left to the receiver at the right (triangles on the base of the 3D grid).
A ray tracing of acoustic wavefronts propagating through the varying density of the ocean. The path can be seen to oscillate about the SOFAR channel.
FF and BF as on-axis points of the front and back (or rear) focal planes of the lens.
FF and BF as on-axis points of the front and back (or rear) focal planes of the lens.
This ray tracing of seismic waves through the interior of the Earth shows that paths can be quite complicated, and reveals telling information about the structure of our planet .