Houdini 20.0 Nodes Geometry nodes

Sky geometry node

Creates a sky filled with volumentric clouds

This node type is deprecated. It is scheduled to be deleted in an upcoming revision of Houdini.

Use the Sky Box node instead.

(Since version 20.0.)

Since 13.0

Deprecated

The Sky SOP is now deprecated. Use Sky Box SOP instead.

This tool will take a bounding box and generate procedural clouds inside. The effect is done at render time but can be visualized in viewport at lower resolution/subdivision level.

Note

The output of this SOP is different when rendering versus interactive. Because it usually is coupled with the CVEX shader, when rendered it outputs an empty geometry. To have a ROP Geometry extract the display geometry, reference the virtual display_sop child node.

Note

The VDB controls only change the detail level in viewport. Since the effect is generated at render time, Volume Step Rate parameter on the Mantra ROP is the main control used to decided how fine the step size is for the volume. For a bounding box that might be in thousands of units, this value might need to be increased. A Volume Step Rate of 1 for procedural CVEX shaders represents 10% of the size.

Tip

Set the input bounding box size before adjusting the parameters since they are dependent on the world scale of the box. If the size is thousands of units make sure to adjust the voxel size.

Tip

The sky can be 'baked' out into an environment map for fast renders. Use a camera with projection set to Polar (panoramic) to render an image that can be used as an environment map.

Parameters

Input

Bounding box for the sky.

VDB

Preview Region

Bounding Box

Generates the clouds inside the bounding box.

Camera Frustum

Generates clouds inside a user specified camera frustum.

Voxel Size

Size of the voxels to be used for preview. This is visible when Preview Region is Bounding Box.

Camera Path

Path to the camera to be used for the viewing frustum volume. This is visible when Preview Region is Camera Frustum.

Z Near

Near clipping plane distance for the camera. This is visible when Preview Region is Camera Frustum.

Z Far

Far clipping plane distance for the camera. This is visible when Preview Region is Camera Frustum.

Uniform Sampling

Specifies the voxel size to be used in the frustum. This is visible when Preview Region is Camera Frustum.

Density

Density Multiplier

Overall density multiplier.

Density Ramp

Allows remapping of the density field.

Coverage

Determines the amount of clouds generated.

Tip

Adjust the Coverage in combination with the Noise Amplitude to get different looks.

Profile Warp

Allows vertical deformation of the generated sky relative to the bounding box center. Useful in shifting distant clouds to meet horizon lines.

Noise

Noise Amplitude

Strength of the noise which is used in displacing the volume. Default value is for 1 unit cube, when increasing the bounding box into thousands of units this value should be adjusted as well.

Noise Element Scale

XYZ size of the noise generated, allows for stretching in a specific axis

Noise Element Size

Overall size of the noise features.

Noise Type

Different noise types to allow.

Roughness

This sharpens or softens the edges of the noise.

Smooth Valleys

This will clear the noise from the low value areas.

Abs Noise

When on this will create absolute noise where each iteration is always positive in value. Turning it off will results in positive and negative values.

Noise Offset

Changes the world space position used by the noise. This can be animated to create noise movement.

Noise Octaves

Number of noise iterations to be used. This controls the amount of detail in the noise.

Mirror

Mirrors the volume on vertical axis.

Top Scale

Allows scaling effect on the generated clouds in the positive Y axis direction

Bottom Scale

Allows scaling effect on the generated clouds in the negative Y axis direction (useful in flattening the bottom of the clouds).

Advection

Advect Amplitude

Amplitude of additional noise offset to the main noise to create finer details.

Advect Element Scale

Per-axis scaling of the noise pattern.

Advect Element Size

The size of the noise pattern.

Advect Octaves

Number of noise iterations to be used. This controls the amount of detail in the noise.

Advect Offset

Position offset of the secondary noise. This can be animated to create noise movement.

Advect Roughness

This sharpens or softens the edges of the secondary noise.

Advect Pulse Length

Size of the 4th component (time) in the advect noise.

Advect Flow

Flow is your position in flowspace. This can be thought of as an extra dimension to your noise, but has a fixed period of 1. Unlike normal approaches to adding another dimension, it operates by rotating the noise vectors, thereby resulting in a flow-like behavior rather than dimension slicing-like behavior.

Advect Flow Rate

Flow rate is analogous to roughness, but applied to the flow dimension. Values greater than 1 appear like turbulence where higher frequencies spin faster than lower frequencies. Values less than one make the finer detail appear to float on the surface of the low-frequency flow.

Self-Advection

The advection term enables backward-tracing of the noise on each successive frequency. This helps the higher frequency noise to stick with the low-frequency flow, but is much more expensive.

Time

Animates the advect noise based on this parameter.

Geometry nodes