# Volume Rendering (Path Tracing & Real-Time)

I have a few doubts and questions regarding volume rendering, I was hoping someone here could help me understand.

1. I commonly hear the terms 'Ray-Marching' & 'Volume Rendering' being used together when it comes to rendering fog or any other volumetric object.

Is Ray Marching the method used to render these volumes such as Fog, Smoke & Fire (this is regarding path tracing)? Since we can use signed distance fields to easily manipulate the shape of the volume? At the approximated intersection point is a BSDF evaluated (BRDF + BTDF) or is it just a BRDF?

1. At the approximated intersection point for the volume what BRDF/BSDF do we use (if we do use one, I might have a wrong understanding of the topic)? Are there measured BRDFs & BTDFs that is the common standard?

So when you perform ray marching along the ray for volume integration, for each step you need to calculate incoming light to that point and evaluate the "phase function" to calculate how much of that light scatters towards the eye. This phase function can be simple isotropic function (i.e. constant $\frac{\rho}{4\pi}$) or more complex anisotropic function such as Mie phase function shown below, depending on the modeled participating media.