The Volume Gradient node can connect to AbsorptionDefines how fast light is absorbed while passing through a medium., ScatteringDefines how fast light gets scattered when traveling through the medium., and Emission ramps in Volume MediumsThe behavior of light inside a surface volume described by scatter, absorption, and transmission characteristics. (figure 1). It differs from a normal texture gradient because it is applies to just a Volume medium node, and takes into account a given maximum grid value based on the grid indices in the volume data set.
Figure 1: The Volume gradient node connected to the Scattering ramp of a Volume MediumA shading system designed to render volumes such as smoke and fog. node
In the color gradient, the colors near the left side of the ramp are mapped to the lower values of the volume with lower density. Colors on the right side of the gradient are mapped to higher grid values where the volume density is greater.
The ramp's Max Grid Value normalizes the volume grid's maximum value,remapping it between 0 and 1 so that the colors on the ramp can map to the volume grid appropriately. The maximum value of grids sometimes differ greatly throughout VDBDreamworks’ open-source C++ library housing the data structures and tools implementation for storing and manipulating volume data, like smoke and other amorphous materials. The purpose of OpenVDB is mostly to have an efficient way to store volumetric data in memory and on disk. It has evolved into a more general toolkit that also lets you accomplish other things, such as fracturing volumes, converting meshes to volumes and vice versa. However, it does not include a computational fluid dynamics solver, and therefore it cannot procedurally generate smoke or fire. OpenVDB is fully integrated as a library in OctaneRender. For more information about OpenVDB, please see http://www.openvdb.org/. sequences from one frame to the next. If the Max Grid Value is set too high or too low, only a subset of the colors in the gradient specified are seen.
Note: The left most color value needs to be white or black, otherwise, the entire volume (including areas without any density) will fill with the specified color.