Piecewise medium (piecewise)

Parameter	Type	Description	Flags
albedo	float, spectrum or volume	Single-scattering albedo of the medium (Default: 0.75).	P, ∂
sigma_t	float, spectrum or volume	Extinction coefficient in inverse scene units (Default: 1). The supplied grid must be of shape [1,1,n].	P, ∂
scale	float	Optional scale factor that will be applied to the extinction parameter. It is provided for convenience when accommodating data based on different units, or to simply tweak the density of the medium. (Default: 1)	P
sample_emitters	boolean	Flag to specify whether shadow rays should be cast from inside the volume (Default: true) If the medium is enclosed in a dielectric boundary, shadow rays are ineffective and turning them

off will significantly reduce render time. This can reduce render time up to 50%

when rendering objects with subsurface scattering.

• • (Nested plugin)

  • phase

  • A nested phase function that describes the directional scattering properties of the medium. When none is specified, the renderer will automatically use an instance of isotropic.

  • P, ∂

This plugin provides a 1D heterogenous medium implementation (plane parallel geometry), which acquires its data from nested volume instances. These can be constant, use a procedural function, or fetch data from disk, e.g. using a 3D grid, as long as the underlying grid has the shape [1,1,N], with N the number of layers on the vertical (z) axis.

The medium is parametrized by the single scattering albedo and the extinction coefficient \(\sigma_t\). The extinction coefficient should be provided in inverse scene units. For instance, when a world-space distance of 1 unit corresponds to a meter, the extinction coefficient should have units of inverse meters. For convenience, the scale parameter can be used to correct the units. For instance, when the scene is in meters and the coefficients are in inverse millimeters, set scale to 1000.

Both the albedo and the extinction coefficient can either be constant or textured, and both parameters are allowed to be spectrally varying.