Volume surface node

Creates a volume primitive.

All

Parameters

Inputs

See also: Volume Mix, Volume Vop, Iso Offset, Iso Surface

The Volume SOP creates a volume primitive. A volume is a box divided up grid of smaller boxes, called voxels, each of which can store a number. The resulting primitive can be used to define a scalar field over a volume sampled at the grid centers.

The grid generated by the Volume SOP has constant value everywhere. It can be further manipulated on a voxel-by-voxel basis using the Volume VOP SOP or the Volume Mix SOP.

When Mantra renders volumes it overrides rendering parameters according to the name of the volume. This name can be set in the Volume SOP (or later using the Name SOP). The name is also used for the default bindings to the Volume VOP SOP.

The Volume SOP can also generate sets of volumes. Selecting a rank of Vector will create three volumes suitable for a velocity field, a rank of Matrix will create nine volumes suitable for a strain tensor field.

Tip

If you connect geometry to the Volume SOP’s input, it will create a bounding box around the input geometry

Parameters

Rank

Each volume primitive only holds a single number per voxel cell. If you want to use higher order volumes, such as vector fields or matrix fields, you can use multiple volume primitives. The Rank option lets you create multiple named volumes to match vector or matrix fields.

Name

If not blank, the created volume primitive will have the name primitive attribute set to this value. Naming volumes allows Mantra and the Volume VOP to override the correct parameters with the values of the volume. If the created volume is Vector or Matrix, .x or .xx will be appended to identify the subcomponents.

Initial Value

The created volume primitive will have the same value throughout the volume.

Size

The size of the volume box. This will be adjusted slightly to ensure voxels are all equal size if uniform sampling is turned on.

Center

The center of the volume box.

Uniform Sampling

It is often advantageous to make sure voxels in a volume are cubes. This option allows the resolution of the volume to be specified without having to worry about matching the size and resolution fields. This parameter controls which axis is divided into Uniform Sampling Divisions.

Uniform Sampling Divisions

The number of voxels to divide the Uniform Sampling axis into. The other axes will be divided into the number of cells that fit for this voxel size.

Sampling Divisions

When using non-uniform voxel cells, each dimensions resolution can be specified here.

Border Type

The behavior when the volume is sampled outside of its defined box.

Constant	The border value will be returned.
Repeat	The volume will wrap, returning values from the opposite side of the volume.
Streak	The value at the edge of the volume closest to the sample will be returned.
SDF	The volume will be treated as a signed distance field. The distance from the sample point to the closest point on the volume will be added to the value at that closest point. This ensures the volume continues to approximate distances outside of its defined box.

Border Value

When the border type is constant, this is the value returned for out of bounds sampling.

Compression Tolerance

When tiles in the volume are compressed this will be the tolerance used for lossy compression. A value of 0 will ensure lossless compression. (Note compression to constant tiles will still occur)

Display Mode

How this volume primitive will be displayed in the viewport. This does not affect the underlying volume at all, just its display-time appearance.

Smoke	The volume is rendered as smoke. Values of 0 or less are fully transparent. If lights are present, they are self-shadowed with the volume.
Rainbow	The volume is rendered as transparent smoke. Values of 0 or less are fully transparent. Lights are ignored, reducing computation time. Instead, the smoke is colored a rainbow hue according to the position in the bounding box.
Isosurface	An isosurface of equal valued voxels is extracted from the volume and displayed. This Display Isocontour is used to determine which isosurface is extracted.
Invisible	The contents of the volume are not rendered at all.

Display Density

Controls the fall off rate for the smoke visualization. Lower values allows the smoke to be more transparent.

Display Isocontour

Which isocontour to extract from the volume. The default of 0 is good for SDF volumes. Fog style volumes would work better with something non-zero, such as 0.5.

Inputs

Bounding source

If you connect geometry to this input, Volume will create a bounding box for the input geometry. (Otherwise, it uses the parameters to control the size and position of the box.)

Usages in other examples

Example name	Example for