Houdini 16.5 Nodes Dynamics nodes

Ground Plane dynamics node

Creates a ground plane suitable for RBD or cloth simulations.

On this page

The Ground Plane DOP creates a ground plane inside the DOP simulation. It creates a new object that has a simple grid geometry attached to it. The grid has a Volumetric Representation attached which simulates an infinitely large plane. This can be used as a collision surface for RBD or Cloth simulations.

Because the ground plane can be moved and reoriented, several ground planes can be used to box in an object.

Using Ground Planes

  1. Click the Ground Plane tool on the Rigid Bodies tab.

Note

You can transform, rotate, scale, and keyframe the ground plane at various frames.

Parameters

Object Name

The name for the created object.

Display Proxy Geometry

The display of the proxy geometry can be turned off.

For more complicated adjustments of the display status, including enabling the rendering of the proxy geometry, use the Rendering Parameters DOP.

Color

The primitive color for the guide grid to be drawn in.

Grid Size

The scale factor for the guide grid. Note that the underlying volumetric representation will continue to infinity, unaffected by this scale factor.

Some culling methods, such as used by the RBD Solver, look at the geometry to determine a bounding volume. These may require a larger grid to ensure the collision with the ground plane is tested.

Initial State

OBJ Path

Allows you to specify the position and rotation of the ground plane based on the position and rotation of an object at the scene level.

Position

The center of the ground plane.

Rotation

The orientation of the ground plane. This is in RX/RY/RZ format.

Physical

Bounce

The elasticity of the object. If two objects of bounce 1.0 collide, they will rebound without losing energy. If two objects of bounce 0.0 collide, they will come to a standstill.

Bounce Forward

The tangential elasticity of the object. If two objects of bounce forward 1.0 collide, their tangential motion will be affected only by friction. If two objects of bounce forward 0.0 collide, their tangential motion will be matched.

Friction

The coefficient of friction of the object. A value of 0 means the object is frictionless.

This governs how much the tangential velocity is affected by collisions and resting contacts.

Dynamic Friction Scale

An object sliding may have a lower friction coefficient than an object at rest. This is the scale factor that relates the two. It is not a friction coefficient, but a scale between zero and one.

A value of one means that dynamic friction is equal to static friction. A scale of zero means that as soon as static friction is overcome the object acts without friction.

Temperature

Temperature marks how warm or cool an object is. This is used in gas simulations for ignition points of fuel or for buoyancy computations.

Since this does not relate directly to any real world temperature scale, ambient temperature is usually considered 0.

Outputs

First

The ground plane object created by this node is sent through the single output.

Locals

ST

This value is the simulation time for which the node is being evaluated.

This value may not be equal to the current Houdini time represented by the variable T, depending on the settings of the DOP Network Offset Time and Time Scale parameters.

This value is guaranteed to have a value of zero at the start of a simulation, so when testing for the first timestep of a simulation, it is best to use a test like $ST == 0 rather than $T == 0 or $FF == 1.

SF

This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.

This value may not be equal to the current Houdini frame number represented by the variable F, depending on the settings of the DOP Network parameters. Instead, this value is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).

TIMESTEP

This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.

SFPS

This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.

SNOBJ

This is the number of objects in the simulation. For nodes that create objects such as the Empty Object node, this value will increase for each object that is evaluated.

A good way to guarantee unique object names is to use an expression like object_$SNOBJ.

NOBJ

This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.

This value may return 0 if the node does not process each object sequentially (such as the Group DOP).

OBJ

This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just the object’s position in the current order of processing.

This value is useful for generating a random number for each object, or simply splitting the objects into two or more groups to be processed in different ways. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

OBJID

This is the unique object identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused.

The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.

This value is also the best way to look up information on an object using the dopfield expression function. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

ALLOBJIDS

This string contains a space separated list of the unique object identifiers for every object being processed by the current node.

ALLOBJNAMES

This string contains a space separated list of the names of every object being processed by the current node.

OBJCT

This value is the simulation time (see variable ST) at which the current object was created.

Therefore, to check if an object was created on the current timestep, the expression $ST == $OBJCT should always be used. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJCF

This value is the simulation frame (see variable SF) at which the current object was created.

This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJNAME

This is a string value containing the name of the object being processed.

Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.

The object name can also be used to treat a number of similar objects (with the same name) as a virtual group. If there are 20 objects named "myobject", specifying strcmp($OBJNAME, "myobject") == 0 in the activation field of a DOP will cause that DOP to operate only on those 20 objects. This value will be the empty string if the node does not process objects sequentially (such as the Group DOP).

DOPNET

This is a string value containing the full path of the current DOP Network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP Network that contains the node.

Note

Most dynamics nodes have local variables with the same names as the node’s parameters. For example, in a Position node, you could write the expression:

$tx + 0.1

…to make the object move 0.1 units along the X axis at each timestep.

Examples

The following examples include this node.

CountImpacts Example for Count channel node

This example demonstrates how to count impacts from a DOPs simulation using the Count CHOP. Then, using the values from the Count CHOP, we generate copies of a teapot.

DynamicLights Example for Dynamics channel node

This example demonstrates how to use the Dynamics CHOP to extract impact data from a DOPs simulation, and then modify the data to control lights in the scene.

DynamicPops Example for Dynamics channel node

This example demonstrates using the Dynamics CHOP to birth particles where an impact occurs, as well as controlling the birth rate based in impulse.

ExtractTransforms Example for Dynamics channel node

This example demonstrates the use of the Dynamics CHOP to pull transformation information out of a DOP simulation and apply it to Objects.

HoldLight Example for Hold channel node

This example uses the Hold CHOP in conjunction with the Dynamics CHOP to hold a light at the position of an impact from a DOPs simulation until a new impact occurs.

Lookup Example for Lookup channel node

This example demonstrates how to use the Lookup CHOP to play animation based on an event, or trigger.

AnimatedActiveState Example for Active Value dynamics node

This example shows how to use the Active Value DOP to animate the Active state of an object. When an object is not active (it is passive), it is not simulated. To keyframe both the active state of an object and its motion while passive, use the RBD Keyframe Active DOP.

AutoFreezeRBD Example for Active Value dynamics node

This example shows a system for automatically detecting when RBD objects achieve a rest state and then turning off their active status. This will freeze them in place reducing computation time and jitter.

LookAt Example for Anchor: Align Axis dynamics node

This example shows how to build a Look At Constraint which keeps a teapot pointed at a bouncing ball. It shows how to build constraints out of anchors and constraint relationships.

BridgeCollapse Example for Apply Relationship dynamics node

This example shows how to use the Apply Relationship DOP to propagate constraints automatically and create an RBD simulation of a collapsing bridge.

ConstrainedTeapots Example for Apply Relationship dynamics node

This example demonstrates how the Apply Relationship DOP can be used to create multiple constraints with the RBD Pin Constraint node.

MutualConstraints Example for Apply Relationship dynamics node

This example demonstrates how to build mutual constraints between two DOP objects using the Apply Relationship node.

SimpleBlend Example for Blend Solver dynamics node

This example demonstrates how to use the Blend Solver. In this case the Blend Solver is used to blend between an RBD solution and a keyframed solution.

BuoyancyForce Example for Buoyancy Force dynamics node

This example shows how to extract a surface field from another object to use as a buoyancy force source.

ClothAttachedDynamic Example for Cloth Object dynamics node

This example shows a piece of cloth attached to a dynamics point on a rigid object.

AnchorPins Example for Constraint Network dynamics node

This example demonstrates how different anchor positions can affect pin constraints.

AngularMotorDenting Example for Constraint Network dynamics node

This example demonstrates how angular motors can be used with pin constraints to create a denting effect.

BreakingSprings Example for Constraint Network dynamics node

This example shows how to use a SOP Solver to break spring constraints in a constraint network that have stretched too far.

Chains Example for Constraint Network dynamics node

This example shows how to create a chain of objects that are connected together by pin constraints.

ControlledGlueBreaking Example for Constraint Network dynamics node

This example shows how to gradually remove glue bonds from a constraint network and control the crumbling of a building.

GlueConstraintNetwork Example for Constraint Network dynamics node

This example shows how to create a constraint network to glue together adjacent pieces of a fractured object. It also shows how primitive attributes such as 'strength' can be used to modify properties of individual constraints in the network.

SpringToGlue Example for Constraint Network dynamics node

This example shows how to create spring constraints between nearby objects, and then change those constraints to glue constraints during the simulation.

AutoFracturing Example for Copy Objects dynamics node

This example shows how to use the Copy Object DOP, in conjunction with a Multi Solver, to automatically break an RBD object in half whenever it impacts another object.

SimpleCopy Example for Copy Objects dynamics node

This example demonstrates the use of the Copy Objects DOP. A single RBD Object is copied 100 times, and assigned a random initial velocity, and a position based on some grid geometry. These 100 spheres are then dropped onto a ground plane.

PartialRagdolls Example for Crowd Solver dynamics node

This example demonstrates how to set up a partial ragdoll, where a subset of the agent’s joints are simulated as active objects by the Bullet solver and the remaining joints are animated.

PinnedRagdolls Example for Crowd Solver dynamics node

This example demonstrates how to set up constraints to attach a ragdoll to an external object, and how to use motors to drive an active ragdoll with an animation clip.

CacheToDisk Example for File dynamics node

This example shows how to use the File DOP to cache a simulation to disk and read it back in.

FEMSpheres Example for finiteelementsolver dynamics node

This example demonstrates how to use the FEM Solver to deform spheres when they collide with the ground plane. The spheres have particle based animation on them prior to collision with the ground and are swapped to the FEM solver on collision.

FlipColorMix Example for FLIP Solver dynamics node

This example demonstrates the use of the Flip Solver to mix the colors of a red fluid with a blue fluid to form a purple fluid.

FlipFluidWire Example for FLIP Solver dynamics node

This example demonstrates the use of the Flip Solver and the Fluid Force DOP. The Fluid Force DOP is used to apply a drag force on a wire object according to the motions of a flip fluid. The drag force is only applied at locations where fluid exists in the fluid object.

BallInTank Example for Fluid Object dynamics node

This example shows an RBD ball being thrown into a tank of liquid.

FluidFeedback Example for Fluid Object dynamics node

This example shows a ball falling into a tank with feedback. This couples the RBD simulation with the Fluid simulation, causing the ball to float rather than sink.

PaintedGrog Example for Fluid Object dynamics node

This example creates a torus of paint which is dropped on the Grog character. The Grog character is then colored according to the paint that hits him. This also shows how to have additional color information tied to a fluid simulation.

GuidedWrinkling Example for Hybrid Object dynamics node

This is a setup for guided wrinkling using the hybrid object. The first sim creates a detailed mesh consisting of both tets and triangles that doesn’t have any wrinkles yet. The second sim is targeted to the animation creates by the first sim and this adds in the wrinkles.

MagnetMetaballs Example for Magnet Force dynamics node

This example demonstrates how to use the Magnet Force node on a group of metaballs to force the fragments of an object outwards at the moment of impact.

SimpleMultiple Example for Multiple Solver dynamics node

This examples demonstrates how to use a Multiple Solver. In this example, the motion of an object is controlled by an RBD Solver while the geometry is modified by a SOP Solver.

Particle fluid buoyancy

This example demonstrates how to couple the Particle Fluid with an RBD object so they both affect each other. The result is a buoyant sphere.

PressureExample Example for Particle Fluid Solver dynamics node

This is a simple example demonstrating pressure-driven flow with no viscosity. This example also demonstrates the use of a constantly emitting source of particle fluid as well as how to surface the fluid using the Particle Fluid Surface SOP.

ViscoelasticExample Example for Particle Fluid Solver dynamics node

This example demonstrates the use of viscous and elastic forces in a particle-based fluid to generate viscoelastic fluid behaviour. The result is a fluid-like object that tends to resist deformation and retain its shape.

ViscousFlow Example for Particle Fluid Solver dynamics node

This example demonstrates highly viscous fluid flow using particle-based fluids. Fluids of this form could be used to simulate slowly-flowing fluids such as lava or mud.

ParticleCollisions Example for POP Collision Detect dynamics node

This example demonstrates the use of the POP Collision Detect node to simulate particles colliding with a rotating torus with animated deformations.

BaconDrop Example for POP Grains dynamics node

This example demonstrates dropping slices of bacon onto a torus. It shows how to extract a 2d object from a texture map and how to repeatedly add the same grain-sheet object to DOPs.

VaryingGrainSize Example for POP Grains dynamics node

This example demonstrates interacting grain simulations of very different sizes.

Stack Example for RBD Auto Freeze dynamics node

Teapots are dropped every ten frames onto a ground plane. The RBD AutoFreeze DOP is used to detect and freeze the teapots that have come to rest, stabilizing and speeding up the simulation.

RagdollExample Example for Cone Twist Constraint dynamics node

This sample creates a simple ragdoll using the cone twist constraint between pieces of the ragdoll.

StackedBricks Example for RBD Fractured Object dynamics node

This example shows how to create a large number of RBD objects from a single SOP. It also shows how a velocity point attribute can be used to set the initial motion for the objects.

BlendSolverWithRBDGlue

This example shows how to grab animated key frame data from an RBD Glue object and blend it into a simulation of a cube fragmenting into multiple pieces on impact.

ChoreographedBreakup

This example shows how one can control the break up of any glued object through the use of the RBD State node.

A torus, composed of spheres, is glued together. An additional sweep plane is defined. Any sphere which ends up on the wrong side of the sweep plane is broken off the torus and left to bounce on its own. This lets the break up of the torus to be controlled over many frames.

ChoreographedTubeBreakup

This example shows how one can control the break up of any glued object through the use of the RBD State node.

In this version of the choreographed breakup example, a moving plane is used to choreograph the breakup of a fractured tube. As the plane passes each piece, it is allowed to break off from the rest of the tube.

ShatterGlass

This example uses an RBD projectile to shatter a piece of glass. The glass is made up of simple trangular shards glued together.

This example also demonstrates a situation where using volume based collision detection would not work, and so the objects are treated as infinitely thin surfaces when performing collision detection.

SimpleKeyActive Example for RBD Keyframe Active dynamics node

This example uses the RBD Keyframe Active node to switch from a keyframed animation to an RBD Solver, and back to keyframed animation. This same animation could be created using a Switch Solver or Blend Solver, but this approach is simpler if the only requirement is switching from keyframed to simulated motion for a few RBD Objects.

DeformingRBD Example for RBD Object dynamics node

This example demonstrates a rigid body dynamics simulation involving deforming geometry. A wobbling torus is dropped onto a ground plane.

FrictionBalls Example for RBD Object dynamics node

This example demonstrates the friction parameter on an RBD Object.

RBDInitialState Example for RBD Object dynamics node

This example demonstrates the use of the Initial State parameter of an RBD object.

SimpleRBD Example for RBD Object dynamics node

This example demonstrates a simple rigid body dynamics simulation using the RBD Object DOP. A single sphere is dropped onto a ground plane.

ActivateObjects Example for RBD Packed Object dynamics node

This example shows how to modify the "active" point attribute of an RBD Packed Object to change objects from static to active.

AnimatedObjects Example for RBD Packed Object dynamics node

This example shows how to use animated packed primitives in an RBD Packed Object and set up a transition to active objects later in the simulation.

EmittingObjects Example for RBD Packed Object dynamics node

This example shows how to use a SOP Solver to create new RBD objects and add them to an existing RBD Packed Object.

Chainlinks Example for RBD Pin Constraint dynamics node

In this chain simulation, the individual chain links react to one another in an RBD sim.

InheritVelocity Example for RBD State dynamics node

This example demonstrates the use of the RBD State node to inherit velocity from movement and collision with other objects in a glued RBD fracture simulation.

Simple Example for RBD Visualization dynamics node

This example demonstrates a simple rigid body dynamics simulation using the RBD Object DOP. A single sphere is dropped onto a ground plane. It adds in an RBD Visualization DOP to show the impact forces that are applied as a result of the collision.

ReferenceFrameForce Example for Reference Frame Force dynamics node

An RBD vase filled with water performs the water simulation in the vase’s reference frame.

RippleGrid Example for Ripple Solver dynamics node

This example demonstrates how to use the Ripple Solver and Ripple Object nodes. Bulge SOPs are used to deform a grid to create initial geometry and rest geometry for the Ripple Object which is then piped into the Ripple Solver.

Freeze Example for Script Solver dynamics node

This example uses the Script Solver to remove objects from the simulation once they fall below a certain threshold velocity. This technique can be used to speed up simulations that are known to settle down to a static arrangement.

ScalePieces Example for Script Solver dynamics node

This example demonstrates how to use the Script Solver node to scale fractured pieces of an RBD sim over time.

SumImpacts Example for Script Solver dynamics node

This example uses the Script Solver and SOP Solver to change the color of RBD objects based on the total impact energy applied to the object at each timestep.

DelayedSmokeHandoff Example for Smoke Object dynamics node

This example shows a way to turn an RBD into smoke a certain number of frames after the RBD object has hit something.

RBDtoSmokeHandoff Example for Smoke Object dynamics node

This example shows a way to turn an RBD object into smoke. It uses multiple different colored smoke fields inside the same smoke object.

VolumePreservingSolid Example for Solid Object dynamics node

This solid object has a strong volume-preserving force (e.g. flesh). The effect of the volume-preserving force is clearly visible when the object hits the ground plane.

VisualizeImpacts Example for SOP Solver dynamics node

An example that shows how you can visualize impact data in an RBD simulation by using a SOP Solver to add custom guide geometry to the RBD Objects.

This example has three toruses falling on a grid with green lines showing the position and magnitude of impacts. The force visualization is added as ancillary geometry data to the actual toruses, so the RBD Solver is entirely unaware of the effect. The SOP Solver could also be used as an independent SOP network to extract impact visualization from an RBD Object.

StaticBalls Example for Static Object dynamics node

This example uses static object nodes in an RBD simulation of a grid falling and bouncing off three spheres before it hits the ground.

FractureExamples Example for Voronoi Fracture Solver dynamics node

This example actually includes eight examples of ways that you can use voronoi fracturing in Houdini. In particular, it shows how you can use the Voronoi Fracture Solver and the Voronoi Fracture Configure Object nodes in your fracture simulations. Turn on the display flags for these examples one at a time to play the animation and dive down into each example to examine the setup.

SimpleVortex Example for Vortex Force dynamics node

This example uses a few balls to visualize the force generated by a Vortex Force DOP.

CompressedSpring Example for Wire Object dynamics node

This example demonstrates how an initial pose may be specified for a wire object.

FadedTorus Example for Attribute Fade geometry node

Here is an example of accumulating and fading an attribute

ConnectedBalls Example for Connectivity geometry node

This example demonstrates how to use an attribute generated by the Connectivity SOP to color different pieces of geometry from a DOPs simulation.

LowHigh Example for Dop Import geometry node

This example shows how to create a low res - high res set up to support RBD objects. The two main methods are to reference copy the DOP Import SOP and feed in the high res geometry or to use point instancing with an Instance Object.

ProxyGeometry Example for Dop Import geometry node

This example demonstrates a technique of using the DOP Import SOP to allow the use of proxy geometry in a DOP simulation. One set of geometries are used in the simulation, then the transform information for those objects is applied to higher resolution versions of the geometry.

dopimportrecordsexample Example for DOP Import Records geometry node

This example demonstrates a creating points for each matching record in the DOP simulation. This lets us create a point for each object or a point for each impact.

glueclusterexample Example for Glue Cluster geometry node

This example shows how to use the gluecluster SOP and glue constraint networks to cluster together the pieces of a voronoi fracture. This allows clustering to be used with Bullet without introducing concave objects.

PartitionBall Example for Partition geometry node

This example demonstrates how to break geometry in a DOPs simulation using the Partition SOP to determine the DOP Objects.

PlateBreak Example for TimeShift geometry node

This example demonstrates how to use the TimeShift SOP to achieve a slow-motion effect during a fracture simulation.

TransformFracturedPieces Example for Transform Pieces geometry node

This example demonstrates using the Transform Pieces SOP to transform high-resolution geometry from the results a DOPs rigid-body fracture simulation that used low-resolution geometry.

Dynamics nodes