Houdini 20.0 Nodes Geometry nodes

Spring geometry node

Simulates the behavior of points as if the edges connecting them were springs.

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

Use the Vellum Solver node instead.

(Since version 17.5.)

On this page

Spring assigns a mass to each point and simulates the effects of forces (gravity, wind, and/or turbulence) on the points. Edges act as springs which try to pull the points back to their original position.

You can:

Tip

The greater the drag value, or smaller the mass, the faster the oscillation dies out.

Note

The Spring SOP is useful for many situations, but for more sophisticated simulations use rigid body, cloth, or wire dynamics.

Note

The Spring SOP will use point normals as initial node velocity if point normal attributes exist and there are no point velocity attributes in the incoming data. If you add velocity attributes to the points, the point normals are ignored.

Parameters

State

StartTime

Time at which the simulation resets.

Preroll Time

Number of initial frames skipped.

Time Inc

Time per iteration.

Accurate Moves

Particles move more accurately.

Attractor Use

How the attractor points affect particles

All points

All points affect each particle

Single point per particle

Only one point affects each particle

Forces

External Force

Force of gravity on points.

Wind

Wind force acting on points.

Turbulence

Amplitude of turbulence along axes.

Turb Period

Inverse variance of turbulence over space.

Seed

Seed for random turbulence generator.

Nodes

Fixed Points

Group of points not to be moved by this operation.

Fixed Points go to Source Positions

Fixed Points are put to their positions in the Source.

Copy Groups from Source

All Source groups are copied at each frame. Useful if the Fixed Points group contents are animated.

Add Mass Attribute

Causes point mass to be calculated.

Mass

Relative mass of each point.

Add Drag Attribute

Causes drag coefficient to be calculated.

Drag

Drag of each point.

Spring Behavior

How the springs will behave

Hooke’s Law

Use Hooke’s law. Force = displacement x spring constant.

Normalize Displacement

Like Hooke’s law except displacement is normalized to the original length of the spring. (Behavior used in Houdini 2.5).

Spring Constant

Stiffness of the spring

Initial Tension

Initial spring tension before deformations.

Limits

+ Limit Plane, - Limit Plane

Points die or bounce off limit planes on contact. /limitposx … /limitposz, /limitnegx …

Hit Behavior

Whether particles die or bounce on limit planes.

Gain Tangent

Energy loss tangent to the collision.

Gain Normal

Energy loss perpendicular to the collision.

Inputs

Spring Source

The points to simulate, for example a polygon sphere or mesh.

Collision Object

(Optional) Geometry for the points to collide with. When the points hit this geometry, they can stick or bounce. If the collision object is deforming, collision detection may fail, causing some points to leak through the collision geometry.

Force

(Optional) A Force SOP, which uses a metaball to create a field which attracts or repels the points.

Examples

BoundLattice

This network utilizes three SOPs (Bound, Spring and Lattice) that commonly work together to simulate certain physical dynamics.

We have created a simple polygonal sphere to act as the source geometry. The sphere is then fed into a Bound SOP which will act as a deforming reference. The Bound SOP also behaves as re-enforcement for the deforming object.

Then the bounding box is wired into the Spring SOP with a group of grids as collision objects. The Spring SOP simulates the dynamics by calculating the proper deformations and behaviours of our source geometry as it collides with other objects. The Spring SOP is where we can apply external forces along with various attributes (characteristics such as mass and drag) which influence how the object deforms.

Finally the Lattice SOP takes the deformation information from the Spring SOP and applies it to the source sphere geometry.

SpringExamples

This example demonstrates the three main functions of the Spring SOP.

It shows how the Spring SOP can deform input geometry to create a cloth like effect by creating interactions between two objects, defining motion, and applying forces.

Play the animation to see the Spring SOP in action.

SpringFlag

This example shows how a flag can be simulated using a Spring SOP.

Here the Spring SOP applies forces that simulate the laws of physics on the points of a Grid SOP to create the flag effect.

SpringHair

This example demonstrates a way to create dynamic hair using the Spring SOP.

A Line is copied onto the points of a Sphere and input into the Spring SOP as a source. Then a Metaball and Force are input to further effect the motion of the hair.

SpringLine

Here the Spring SOP is used to give a line rubber band-like characteristics. Used in combination with an Xform SOP, the rubber band dances about on the floor.

Geometry nodes