Controls the overall size of the sky region that is filled with clouds.

Controls the overall position of the sky region that is filled with clouds.

When this is on and geometry is connected to the third input, this node uses the bounding box of the third input instead of the Size and Center parameters. Turn this off to ignore anything connected to the third input and use Size and Center instead.

Use the convex hull of the points for activation.

Ignores the Y components of Size and Center , and calculates them using the Altitude and Thickness parameters.

The position on the Y-axis where the bottom of the cloud sits. Increase the number to position to cloud higher up in the atmosphere. Make sure this altitude falls into the bounding box given by Size and Center.

When a Sky Field named altitude is wired into this node’s second input, change the menu on the right side of this parameter from Set Uniform to Use Sky Layer to overwrite the value of the parameter using the Sky Field.

The vertical extent of the cloud. Smaller wispy clouds might require a thin layer, while large billowy clouds usually need a larger thickness. Make sure this altitude falls into the bounding box given by Size and Center.

When a Sky Field named thickness is wired into this node’s second input, change the menu on the right side of this parameter from Set Uniform to Use Sky Layer to overwrite the value of the parameter using the Sky Field.

Allows vertical deformation of the generated sky to create a sky dome. This is useful in shifting distant clouds to meet horizon lines.

Sets the position on the Y-axis where the bottom of the sky dome sits.

The radius of the sky dome. Increase this value to create a larger sky dome.

Controls the center position of the sky dome. Use this control when the sky dome is not located at the origin.

This ramps controls the curvature of the sky dome based on the distance from the center of the sky dome.

When you convert a Sky Field (connected to the second input) to 3D clouds, the results might be visually displeasing. You can try turning on this option, which adds noise to the sampling points across the 3D Sky Box.

When Sample With Noise is on, this is the strength of the noise used to vary the sampling position. Larger values create more broken-up shapes, but also could distort the look of the Sky Field.

Uniform scale of elements in the noise.

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want but want to get a different set of values for a different look, try changing the offset.

The scale increment between iterations of fractal noise added to the basic output. The higher the value the larger the “jaggies” added to the output. You can use a negative value for roughness.

Scales the falloff from cloud to emptiness at the top of the cloud, from 0 to 1 relative to the Thickness of the Sky Box. Raising the first number gives the top of the clouds more density before they fall off. Lowering the second number makes the density at the top of the clouds fall off faster.

When a Sky Field named topprofile is wired into this node’s second input, change the menu on the right side of this parameter from Set Uniform to Use Sky Layer to overwrite the value of the parameter using the Sky Field.

Controls how flat the top of the clouds should appear.

Scales the falloff from cloud to emptiness at the bottom of the cloud, from 0 to 1 relative to the Thickness of the Sky Box. Raising the first number gives the bottom of the clouds more density before they fall off. Lowering the second number makes the density at the bottom of the clouds fall off faster.

When a Sky Field named bottomprofile is wired into this node’s second input, change the menu on the right side of this parameter from Set Uniform to Use Sky Layer to overwrite the value of the parameter using the Sky Field.

Controls how flat the bottom of the clouds should appear.

Raises the vertical thickness of the cloud relative to its given thickness (given by Thickness). If the thickness is set to 100 and this parameter is 1, the overall vertical thickness of the cloud will be 200.

When a Sky Field named verticalextrusion is wired into this node’s second input, change the menu on the right side of this parameter from Set Uniform to Use Sky Layer to overwrite the value of the parameter using the Sky Field.

The generated sky region is always clipped according to the given bounds. When the skybox is large enough, this clipping might not be visible. However, when only a small patch of clouds is needed, turn on this control to create a much more natural boundary based on a spacial noise. The boundary is always eroded in an oval shape.

Controls how much cloud area erodes away from the boundary. Larger values will leave a smaller sky region with clouds, but their boundary will be more broken up.

Uniform scale of elements in the spacial noise that is used for erosion.

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

This value expands or shrinks the overall range of tonal values. Particularly, each noise value is pushed towards (if Contrast is less than 1) or away from (if Contrast is greater than 1) medium grey (noise values at 0.5).

When this is turned on, sizes and positions the voxels of the VDB based on the frustum of a camera object.

The path to the camera object to align the VDB to. For example, /obj/cam1.

The distance, in Houdini units, from the camera to the near side of the frustum used to calculate voxel size.

The distance, in Houdini units, from the camera to the far side of the frustum used to calculate voxel size.

The type of noise to generate. Different algorithms give noise with different characteristics.

Perlin Cloud

Generates a perlin noise-based cloud pattern influenced by the Distortion parameter.

Perlin noise with Distortion set to -1 (left) and +1 (right):

Simplex Cloud

Generates a simplex noise-based cloud pattern influenced by the Distortion parameter. Simple noise is similar to Perlin, but the noise lattice is on a tetrahedral mesh rather than a grid. This can avoid the grid patterns often visible in Perlin noise.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Fast Simplex Cloud

Generates a fast simplex noise-based cloud pattern influenced by the Distortion parameter. This simplex noise function uses a different lattice structure and a cheaper accumulation method.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

Generates an additional alligator noise that is combined with the default billowy noise. Use the Vertical Profile Mask in the Mask folder to control the vertical blending of this noise.

Controls how much the alligator noise will affect the default billowy noise.

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

Controls the overall gamma of the generated noise. Values less than 1 will darken the noise, increasing the range of values in originally bright areas. Conversely, values greater than 1 will stretch out the range of values for originally dark areas, which will increase the overall brightness of the noise.

This value expands or shrinks the overall range of tonal values. Particularly, each noise value is pushed towards (if Contrast is less than 1) or away from (if Contrast is greater than 1) medium grey (noise values at 0.5).

The number of iterations of distortion to add to the output of the basic noise. The more iterations you add, the more “detailed” the output. Note that the output may have fewer octaves than this parameter (that is, increasing the parameter will eventually stop adding detail), because the node eventually stops when there’s no more room to add more detail in the output.

The frequency increment between iterations of fractal noise added to the basic output. Note that you can use a negative value.

The scale increment between iterations of fractal noise added to the basic output. The higher the value the larger the “jaggies” added to the output. You can use a negative value for roughness.

This ramp lets you control the strength of the alligator noise function across the vertical profile of the skybox. The horizontal axis represents the vertical height (minimum on the left, maximum on the right). The vertical axis represents the strength of output when the noise function generates that point within the range.

Generates a fine, feather like wispy noise that can be combined or overwritten by the default billowy noise. Use the controls inside the Mask folder to change the blending with the billowy noise.

Controls the strength of the wispy noise. Larger values create finer and more broken up shapes, while lower values create smoother wispy details.

When Attribute Type is Vector, click the Per Component button for separate amplitudes along each axis.

When Attribute Type is Vector and you turn on the Per Component button, this lets you scale the Amplitude separately across each axis.

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

When enabled, a turbulence noise is generated to displace the default wispy noise to create additional finer wispy details.

The type of noise to generate. Different algorithms give noise with different characteristics.

Fast

The default. A faster and more interesting variant of Perlin noise.

Sparse Convolution

Sparse Convolution noise is similar to Worley noise. Does not have artifacts at grid points.

Alligator

Produces a bumpy output. Named for its alleged resemblance to alligator skin.

Perlin

A noise where the visual details are the same size. Wikipedia article

Perlin Flow

A noise that’s stable over time, like a rotated Perlin noise, useful to create noise that seems to swirl and flow smoothly across time. Use the Flow rotation parameter below to control the rotation.

Simplex

A noise similar to Perlin but the noise lattice is on a tetrahedral mesh rather than a grid. This can avoid the grid patterns often visible in Perlin noise.

Worley Cellular F1

Produces cellular features similar to plant cells, ocean waves, honeycombs, cratered landscapes, and so on. Wikipedia article

Worley Cellular F2-F1

A variant of Worley noise that produces blunted and cornered features.

Manhattan Cellular F1

A variant of Worley F1 noise that uses Manhattan distance calculation. Useful when you want unusual-looking noise.

Manhattan Cellular F2-F1

A variant of Worley F2-F1 noise that uses Manhattan distance calculation. Useful when you want unusual-looking noise.

Chebyshev Cellular F1

A variant of Worley F1 noise that uses Chebyshev distance calculation. Useful when you want unusual-looking noise.

Chebyshev Cellular F2-F1

A variant of Worley F2-F1 noise that uses Chebyshev distance calculation. Useful when you want unusual-looking noise.

Perlin Cloud

Generates perlin noise based cloud pattern influenced by the Distortion parameter.

Perlin noise with Distortion set to -1 (left) and +1 (right):

Simplex Cloud

Generates simplex noise based cloud pattern influenced by the Distortion parameter. Simplex noise similar to Perlin, but the noise lattice is on a tetrahedral mesh rather than a grid. This can avoid the grid patterns often visible in Perlin noise.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Fast Simplex Cloud

Generates fast simplex noise based cloud pattern influenced by the Distortion parameter. This simplex noise function uses a different lattice structure and a cheaper accumulation method.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Controls the strength of the turbulent noise. Larger values create finer and more broken up shapes, while lower values create smoother wispy details.

When Attribute Type is Vector, click the Per Component button for separate amplitudes along each axis.

When Attribute Type is Vector and you turn on the Per Component button, this lets you scale the Amplitude separately across each axis.

Flattens the noise to prevent extreme spikes by damping the values. Higher values create a smoother look.

Vary the generated noise with time. This controls the rate of change of the noise pattern.

The time at which to evaluate the cloud noise.

When turned on, offsets the evaluated noise patterns that gives the visual effect of “panning” across the noise field simulating a wind like effect.

Controls how fast the noise pattern movies in the direction given by Direction.

The direction that is used to offset the noise pattern.

When turned on, this controls how much the direction (given by Direction) will blend towards the Y-axis. Use this control to add a small amount of upwards motion to the direction.

Controls the offset difference between the bottom and the top of the skybox.

With reduced coverage values (given by Coverage) the density output by the skybox is also reduced. When this is turned on, the density range will more closely match the 0 to 1 range.

When the checkbox is on, clamp density values so they are never greater than this value.

Multiplies the density using this value in the regions where billowy noise is generated.

Multiplies the density using this value in the regions where the wispy noise is generated. Generally, wispy noise is more opaque than a filled billowy cloud.

Turn this on to shape the output of the density with a ramp.

When Enable Remap Ramp is on, this ramp lets you control the density output. The horizontal axis represents the input density range (minimum on the left, maximum on the right). The vertical axis represents the number to output when the density value is at that point within the range.

Turn this on to shape the output of the density along the vertical profile of the skybox.

This ramp lets you control the output density across the vertical profile of the skybox. The horizontal axis represents the vertical height (minimum on the left, maximum on the right). The vertical axis represents the density scale to output when the noise function generates that point within the range.

Deactivates any voxels that have the background value. This is useful for cleaning up the result of an operation that may have speculatively activated a large band of voxels, but may not have placed non-background values in all of them.

For example, you may have a VDB Activate before a Volume VOP with Expand turned on to ensure you have room to displace the volume. Then you can use one with Deactivate to free up the voxels you didn’t need to use.

Computes the minimum and maximum values of the density volume given by Density Volume.

The name of the volume to be used as density for the cloud box. Usually you should leave it as density.