What is the difference between ray tracing, ray casting, ray marching and path tracing?

Question

As far as I know, all the techniques mentioned in the title are rendering algorithms that seem quite similar. All ray based techniques seem to revolve about casting rays through each pixel of an image which are supposed to represent rays of real light. This allows to render very realistic images.

As a matter of fact I am making a simple program that renders such images myself based on Raytracing in one Weekend.

Now the thing is that I wanted to somehow name this program. I used the term “ray tracer” as this is the one used in the book.

I have heard a lot of different terms however and I would be interested to know what exactly is the difference between ray tracing, ray matching, ray casting, path tracing and potentially any other common ray-related algorithms. I was able to find some comparisons of these techniques online, but they all compared only two of these and some definitions overlapped, so I wanted to ask this question about all four techniques.

Answer 1

My understanding of this is:

1. ray cast

   is using raster image to hold the scene and usually stop on first hit (no reflections and ray splitting) and does not necessarily cast ray on per pixel basis (usually per row or column of screen). The 3D version of this is called Voxel space ray cast however the map is not voxel space instead 2 raster images RGB,Height are used.

   For more info see:

   • ray cast
   • Voxel space ray casting

2. (back) ray trace

   This usually follows physical properties of light so ray split in reflected and refracted and we stop usually after some number of hits. The scene is represented either with BR meshes or with Analytical equations or both.

   for more info see:

   • GLSL 3D Mesh back raytracer
   • GLSL 3D Volumetric back raytracer

   the back means we cast the rays from camera to scene (on per pixel basis) instead of from light source to everywhere ... to speed up the process a lot at the cost of wrong lighting (but that can be remedied with additional methods on top of this)...

The other therms I am not so sure as I do not use those techniques (at least knowingly):

1. path tracing

   is optimization technique to avoid recursive ray split in ray trace using Monte Carlo (stochastic) approach. So it really does not split the ray but chose randomly between the 2 options (similarly how photons behave in real world) and more rendered frames are then blended together.

2. ray marching

   is optimization technique to speed up ray trace by using SDF (signed distance function) to determine safe advance along the ray so it does not hit anything. But it is confined only to analytical scene.