---
title: "Volumetric Grid"
canonical: "https://documentation.chaos.com/space/DOCSGUIDE/113291564/Volumetric%20Grid"
format: markdown
---
A *volumetric grid* is a framework used to generate and render gaseous and liquid effects such as fog, clouds, fire, smoke, and ocean water. It is also sometimes called simply a *volumetric* or a *volume*.

 

## **Overview**

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In computer renderings, it is difficult to realistically depict gases and liquids using solid objects. For this reason, the volumetric grid was developed as a way to create these effects.

A volumetric grid is made up of *voxels*, which can be thought of as three-dimensional pixels. The term comes from combining the words *volume* and *pixel*. Voxels are also sometimes called *cells*.

(PICTURE)

## **Voxel Properties**

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Like pixels in a 2D image, each voxel in a volumetric grid can have a number of properties. The most common are:

- Color - Just like a pixel in an image, each voxel can have a single color assigned to it.
- Opacity - Also like a pixel in an image, each voxel has a uniform opacity assigned to it.
- Full/empty - Some voxels won't have any information in them. For example, the voxels near the corners of the grid are almost always empty. Having a full/empty property makes rendering faster, as these voxels aren't considered at all in the rendering.

It is important to note that any one voxel is either full or empty, and has a *single* color and opacity assigned to it. A single voxel cannot be partially empty or full, or have varying opacity or colors across it.

In the simple example below, a very coarse volumetric grid is set up to create a cloud. The voxels near the outer edges of the grid are empty. Near the center of the grid, voxels are white with nearly 100% opacity. Voxels in between the center and edges are white or gray with less than 100% opacity, with those nearest the empty cells having very low opacity.

(PICTURE)

The grid shown above would be considered far too coarse to to get a realistic effect. In practice, it is usually necessary to have millions of voxels within a single volumetric grid to create a realistic effect. 

Additional Voxel Properties

Light-emitting