Houdini 13.0 Nodes

interface version 1

A an alternative for the Advect by Volumes POP that uses point clouds.

This is the same operator as the Advect by Volumes POP node, but instead of volumes, it uses a vector attribute from a SOP point cloud to advect particles. Otherwise it’s exactly identical to the aforementioned POP.

There are certain situations where a pointcloud-based approach is preferable over a volume-based one – especially when considering efficiency. A good example is advecting particles along curves: using a volume-based approach in such cases is an overkill in terms of both memory/storage and computation time.

The point cloud-based approach is an useful complementing tool for the original volume-based advection node.

Supported per-point attributes

forcescale

Overrides the Force Scale parameter (Update Force mode).

velscale

Overrides the Velocity Scale parameter.

velscale_final

Overrides the Final Velocity Scale parameter (Update Position mode).

Parameters

(Only specific parameters are documented – see the Advect by Volumes operator documentation for parameter descriptions not mentioned here.)

Velocity Geometry

Path to a SOP geometry with a per-point vector attribute to be used for advection.

Velocity Attribute

Name of a vector attribute on the point cloud to use for advection.

Lookup radius

No points further than this distance will affect the particle.

Number of Points

The maximum number of points to consider from the point cloud when advecting the particle.

Tip

Pointcloud-based advection (and point cloud-lookup in general) works by considering neighbouring points in the pointcloud, and calculating their average.

The lookup starts from the 3d position of the point to be advected, and the pointcloud points are considered, sorted by distance. The lookup is completed either the lookup radius is reached or the number of lookup points are reached. (e.g. for dense point clouds, if the max number of points are low, the actual lookup radius will always be low, regardless of the radius setting.)

Todo

  • Update Position/Velocity Update

    • add option to use retrieved velocity values

Release Notes

interface version 1

2013-02-20
  • Added “Final Velocity Scale” parameter (position update mode)

  • Added list of supported per-point attributes

2013-02-17
  • Fix: Final Velocity in Position mode wasn’t using the Velocity Scale parameter: fixed.

2013-02-14
  • Bug fix: replaced leftover volume-advection (position branch, final velocity).

  • Behaviour fix: previously, velocity and position modes stopped particles that fell outside the point cloud’s range. Now they are to continue on course. (A side effect is that cloud points with zero-length vectors are ignored, so they can’t be used to stop particles. For that purpose, use near-zero vector lengths.)

2013-02-14

First version. (Also, fixed a minor issue when normals were used to advect.)