This node will advect the points in a particle system along a velocity field. The first thing you need is a particle system to use. Node inputs are:

• Particle System - Particle system to advect
• Velocity Grid - This must be a vector-valued VDB primitive. You can use the Vector Merge node to turn a vel. [xyz] triple into a single primitive
• Closest Point Grid - Used for projection and constrained advection

In the node's panel, the controls are as follows:

• Type - Three types are proposed:
  • Advection - Move the point along the velocity field
  • Projection - Move the point to the nearest surface point
  • Constrained Advection - Move the along the velocity field, and then project using the closest point field. This forces the particles to remain on a surface
• Integration - Later options in the list are slower but better at following the velocity field
• Iterations - Number of times to try projecting to the nearest point on the surface. Projecting might not move exactly to the surface on the first try. More iterations are slower but give a more accurate projection
• Steps - How many times to repeat the advection step This will produce a more accurate motion, especially if large time steps or high velocities are present
• Add Particles - At each frame add the input particles to the advection
• Lifespan - How many frames the advected points will live for

This node presents various grid manipulations. Depending on the input grid type and the operation the output grid type will vary. Once an input is connected and the grid type is known the list of available operations will be collapsed to only show appropriate choices. Finally, if you change the operation the grid output will disconnect (ie scalar to vector).

• Gradient - Vector that points perpendicular to the values basically un-normalized normals (Scalar - Vector)
• Curvature - A measure of the surface curvature (Scalar - Scalar)
• Laplacian - A smoothed version of the input (Scalar - Scalar)
• Closest Point Transform - Direction to the closest point (Scalar - Vector)
• Divergence - A measure of the change in quantities (Vector - Scalar)
• Curl - A direction perpendicular to the input grid vectors (Vector - Vector)
• Magnitude - The scale of the input vectors (Vector - Scalar)
• Normalize - Normalized input vectors (Vector - Vector)

There is also a Scale input for further adjustment.

Combines grids using scalar operations.

• Combination type - The different math operators that can be brought to bear:
  • Copy A - Use A , ignore B
  • Copy B - Use B, ignore A
  • Invert - Use 1 minus A
  • Add - Add the values of A and B (Using Add for fog volumes, which have density values between 0 and 1, will push densities over 1 and cause a bright interface between the input volumes when rendered. To avoid this problem, try using the Blend 2 option)
  • Subtract - Subtract the values of B from the values of A
  • Multiply - Multiply the values of A and B
  • Divide - Divide the values of A by B
  • Maximum - Use the maximum of each corresponding value from A and B (Using this for fog volumes, which have density values between 0 and 1, can produce a dark interface between the inputs when rendered, due to the binary nature of choosing a value from either from A or B. To avoid this problem use Blend 1 instead)
  • Minimum - Use the minimum of each corresponding value from A and B
  • Blend 1 - (1 - A) * B. This is similar to SDF Difference, except for fog volumes, and can also be viewed as a "soft cutout" operation It is typically used to clear out an area around characters in a dust simulation or some other environmental volume
  • Blend 2 - A + (1 - A) * B. This is similar to SDF Union, except for fog volumes, and can also be viewed as a "soft union" or "merge" operation. Consider using this over the Maximum or Add operations for fog volumes

The node tree will synchronize your surface morphing at the same time as the geometry

The first four controls are graded in terms of rapidity and quality. Change up from the first only if it is posing you problems with how the Morph is playing out.

• Normalizing Steps - After morphing the signed distance field, it will often no longer contain valid distances. A number of renormalization passes can be performed to convert it back into a proper signed distance field
• Speed - A scalar to determine how fast your morph occurs
• Invert Alpha Mask - If you have hooked up a grid as an alpha mask, this option allows you to reverse what is alpha'ed out

Introduction

Partio is an open-source C++ library, created by the Walt Disney Animations Studio, for reading, writing and manipulating a variety of standard particle formats (GEO, BGEO, PTC, PDB, PDA). LightWave cannot support the BGEO format, but Houdini can save in the older HClassic format that LightWave will understand. To save in HClassic format, just replace the file extension in Houdini.

The Partio node has a single output - Particle System. To see these outputs, add an Additional > ParticleInfo node.

Using the Partio node with a From Particles node

Don't forget to turn on 'Use Legacy Volumetrics' In the Render Properties > Volumetrics tab

You can also use LightWave's own Volumetric objects. Add another null called "vol". Set the vol null Primitive Type to Volumetric. Use an OpenVDB Evaluator Object Replacement in the Partio's Object Properties window. In the Node Editor, add a Partio node and bring in your Houdini HClassic files. Set the Partio node Target to the vol null.

Hook the Partio node directly to the Destination OpenVDB node. This will output a particle system. Add a new null labeled "vol" and make it a Volumetric object. Set the source item here to vol.

New to LightWave 2020 is a pair of nodes to split level sets into three separate dimensions for further manipulation. The

Vector Split node takes an incoming OpenVDB grid and splits it into X, Y and Z channels. There is no options panel.

The Vector Merge node will create a vector-valued VDB volume using the values of corresponding voxels from up to three scalar VDBs as the vector components. The scalar VDBs must have the same voxel size and transform; if they do not, use the Resample node to resample two of the VDBs to match the third.

This node offers the following types of operation:

• Tuple - No transformation
• Gradient - Inverse-transpose transformation, ignoring translation
• Unit Normal - Inverse-transpose transformation, ignoring translation but with renormalization
• Displacement - Transformation, ignoring translation
• Position - Transformation with translation
• Copy Inactive Values - If enabled, merge the values of both active and inactive voxels. If disabled, merge the values of active voxels only, treating inactive voxels as active background voxels wherever corresponding input voxels have different active states

Additional Destination node to help visualize VDB networks. You can choose any combination of the three choices -Values, Voxels, and Extent. When this node uses a Velocity Grid output as its input, the Vector Options dropdown menu becomes available.

• Show Values - Shows the scalar voxel values multiplied by color
• Show Voxels - Show the voxel cubes
• Show Extent - Puts a box surrounding the voxel object showing the extents
• Vector Options - A dropdown menu with three options. This menu is ghosted when the Visualize node is not hooked to a Velocity Grid
  • Velocity - Shows velocity unclamped transformed
  • Normal - Shows normals scaled to .4 of box size to prevent overlap. Inverse transformed
  • Color - Shows the color with no transform