nParticleShape

Lifespan

Lifespan attributes provide a number of ways to specify how particle lifespan is determined.

Particle Size

Radius

Determines the overall radius of the nParticle object. The Radius setting provides the input value for the Radius Scale ramp.

Radius Scale Randomize

Sets a random multiplier for the per-particle attribute values.

Collisions

Collide

When on, the current nParticle object collides with passive objects, nCloth objects, and other nParticle objects that share the same Maya Nucleus solver. When off, the current nParticle object does not collide with passive objects, nCloth objects, or other nParticle objects that share the same Maya Nucleus solver.

Self Collide

When on, particles generated by the nParticle object collide with each other. When off, these particles do not collide with each other.

Collide Strength

Specifies the strength of collisions between nParticles and other Nucleus objects. At the default value of 1, nParticles fully collide with each other and with other Nucleus objects. Collide Strength values between 0 and 1 dampen the full collision, while 0 turns off nParticle collisions (which has the same as effect as turning off the object's Collide attribute). Setting Collide Strength to values greater than 1 slightly increases the force of collisions, while values less than 0 can create a weak repulsive force between objects.

You can set Collide Strength on a per-particle basis with a Collide Strength Scale ramp.

Collision Layer

Assigns the current nParticle object to a specific collision layer. Collision Layers determine how nParticle, nCloth, and passive objects that share the same Maya Nucleus solver interact.

nParticle objects on the same collision layer collide normally. However, when nParticle objects are on different layers, particles on lower value layers will have priority over particles on higher value layers. So an nParticle object on collision layer 0.0 will push an nCloth object or another nParticle object on collision layer 1.0, which in turn will push an nCloth object or another nParticle object on collision layer 2.0. This collision priority occurs in the range set by the Collision Layer Range attribute on the nucleus node.

Note

nCloth and Passive objects in collision layers only collide with nParticle objects that are in the same collision layer, or in layers of higher value.

See Collision Layer in the nClothShape node description.

Collide Width Scale

Specifies a collision scale value for collisions between the current nParticle object and other nucleus objects.

Self Collide Width Scale

Specifies a self-collision scale value for the current nParticle object. Self Collide Width Scale allows you to scale the thickness of collisions that occur between particles emitted from the same nParticle object. Setting Self Collide Width Scale improves the smoothness of particle emission of self colliding particles, and speeds up the simulation. Self Collide Width Scale is 1.0 by default.

Display Color

Specifies the color of the collision volumes for the current nParticle object. Display Color is only visible when your scene view display mode is set to Shading > Smooth Shade Selected Items or Shading > Flat Shade Selected Items.

Bounce

Specifies the springiness or bounciness of the current nParticle object. Bounce determines the amount of the nParticle’s deflection or rebound on collision with itself, passive objects, nCloth or other nParticles objects that share the same Maya Nucleus solver.

The amount of Bounce an nParticle object should have is determined by the type of nParticle effect. For example, nParticles with a Bounce of 0.0 would not be bouncy (such as steel) and an nParticle with a Bounce of 0.9 would be very bouncy (such as rubber). Bounce is 0.0 by default.

Note

Bounce values greater than 1.0 can cause instability and should be avoided.

Friction

Specifies the amount of friction for the current nParticle object. Friction determines how much nParticles resists relative motion on collision with itself, passive objects, nCloth, and other nParticle objects that share the same Maya Nucleus solver.

The amount of Friction an nParticle object should have is determined by the type of nParticle effect. The affect of Friction is influenced by the nParticle object’s Stickiness value. See Stickiness.

Stickiness

Stickiness specifies the tendency of nParticles to stick to other Nucleus objects when nCloth, nParticle, and passive objects collide.

Stickiness and Friction are similar attributes in that Stickiness is an adhesion force in the normal direction, while Friction is a force acting in the tangent direction. As with Friction, the Stickiness value used in a collision is the sum of the two colliding objects. So, for full sticking, the Friction and Stickiness on the colliding objects should be 1.0. Note that if Stickiness and Friction are both set to 2 on an object, this object will stick to other Nucleus objects that have Stickiness set to 0.

For particles from the same nParticle object to stick to each other, Self Collide must be turned on.

Max Self Collide Iterations

Specifies the maximum number of iterations per simulation step for the current nParticle object's dynamic self collisions. Max Self Collide Iterations clamps the number of iterations to prevent high level property values or a large number of steps from locking up the nParticle object.

Dynamic Properties

Forces In World

If you prefer that a field affect a particle object in its local space, select the particles, display the Attribute Editor, and turn off Forces In World.

Note that the orientation of the local axes of a particle object matches the orientation of the world space axes unless you rotate the object.

Tip

If you have not keyed, parented, or otherwise controlled the transform attributes of a particle object, you can turn off Forces In World to speed up dynamic calculations for the object. When Forces In World is on, Maya does extra computations to convert world space to local space coordinates.

See Apply forces in an object’s local space.

Ignore Solver Gravity

When on, solver Gravity is disabled for the current nParticle object.

Ignore Solver Wind

When on, solver Wind is disabled for the current nParticle object.

Local Force

Applies a force similar to Nucleus Gravity to the nParticle object in the amount and direction specified. The force is applied locally and does not affect other Nucleus objects assigned to the same solver.

The total force acting on the nParticle, is the sum of the set Nucleus Gravity and Local Force. For example, to double the force of gravity acting on the object, set the Local Force Y value to -9.8. Turn on Ignore Solver Gravity if you want only the Local Force to affect your nParticle object.

Local Wind

Applies a force similar to Nucleus wind to the nParticle object in the amount and direction specified. The wind is applied locally and does not affect other Nucleus objects assigned to the same solver.

The total wind acting on the nParticles is the sum of the set Nucleus wind and Local Wind. Turn on Ignore Solver Wind if you want only the Local Wind to affect your nParticle object.

Dynamics Weight

A value of 0 causes fields, collisions, springs, and goals connected to the particle object to have no effect. A value of 1 provides the full effect. A value less than 1 sets a proportional effect. For example, 0.6 scales the effect to 60% of full strength.

Expressions are unaffected by Dynamics Weight.

Conserve

The Conserve value controls how much of a particle object’s velocity is retained from frame to frame. Specifically, Conserve scales a particle’s velocity attribute at the beginning of each frame’s execution. After scaling the velocity, Maya applies any applicable dynamics to the particles to create the final positioning at the end of the frame.

Conserve doesn’t affect motion created by keyframes. Keyframes affect only a particle object’s worldVelocity attribute, not its local velocity attribute.

If you set Conserve to 0, none of the velocity attribute value is retained. The velocity is reset to 0 before each frame. At the end of each frame, the velocity is entirely the result of dynamics applied during that frame.

If you set Conserve to 1, the entire velocity attribute value is retained. This is the real-world physical response.

If you set Conserve to a value between 0 and 1, a percentage of the velocity attribute value is retained. For example, if you set Conserve to 0.75, each frame Maya first reduces the velocity attribute 25%, then it calculates any dynamic or expression effects on the object.

For example, suppose you create a particle falling with the acceleration of gravity, 9.8 units per second per second. The following table compares how Conserve values of 1 (default), 0.5, and 0 affect the velocity attribute after several frames execute.

Frame	Velocity with Conserve = 1	Velocity with Conserve = 0.5	Velocity with Conserve = 0
2	<<0,0,0>>	<<0,0,0>>	<<0,0,0>>
3	<<0,-0.41,0>>	<<0,-0.41,0>>	<<0,-0.41,0>>
4	<<0,-0.82,0>>	<<0,-0.61,0>>	<<0,-0.41,0>>
5	<<0,-1.23,0>>	<<0,-0.71,0>>	<<0,-0.41,0>>
6	<<0,-1.63,0>>	<<0,-0.77,0>>	<<0,-0.41,0>>

With Conserve set to 1, velocity increases each frame at the exact acceleration rate of gravity.

With Conserve set to 0, velocity stays a constant value—the particles do not accelerate. At the beginning of each frame, velocity is reset to 0. The gravity field’s acceleration is then added to the velocity of 0, which results in the same number <<0,-0.41,0>> being used at the end of each frame.

With Conserve set to 0.5, velocity increases each frame at a much slower rate than gravity. At the beginning of each frame, velocity is scaled to 50% of the value it had at the end of the prior frame. The acceleration of gravity is then added to this scaled value to create the slowly increasing velocity used at the end of the frame.

Drag

Specifies the amount of drag applied to the current nParticle object. Drag is the component of aerodynamic force parallel to the relative wind which causes resistance. Drag is 0.05 by default.

Damp

Specifies the amount the motion of the current nParticles are damped. Damping progressively diminishes the movement and oscillation of nParticles by dissipating energy.

Mass

Specifies the base mass of the current nParticle object. Mass determines the density or the weight of an nParticle object when its Maya Nucleus solver’s Gravity is greater than 0.0.

The Mass an nParticle should have is determined by the type of nParticle effect you want to achieve.

Mass affects behavior in collisions and behavior with Drag. nParticles with high Mass have greater influence on other nParticle or nCloth objects with low Mass, and they are less influenced by Drag.

Force Field Generation

Generates a force field that can push (positive fields) nCloth objects and other nParticle objects away from the current nParticles, and pull (negative fields) nCloth objects and other nParticle objects toward the current nParticles. A Point Force Field can only be exerted on Nucleus objects that are assigned to the same Nucleus solver as the nParticle object generating the Point Force Field.

See Force Field Generation.

Point Field Magnitude

Sets the strength of the Point Force Field. Positive Point Field Magnitude values push nCloth objects and other nParticle objects away from the current nParticles. Negative Point Field Magnitude values pull nCloth objects and other nParticle objects toward the current nParticles.

Self Attract

Sets the strength of self attractive forces between the points (individual particles) of an nParticle object. Positive Self Attract values pull the points (individual particles) of an nParticle object together. Negative Self Attract values push the points (individual particles) away from each other.

Point Field Distance

Sets the distance (in field units) from the radius of the force generating nParticle that the Point Force Field is active. Outside the Point Field Distance, the Point Force Field does not affect nCloth objects and other nParticle objects.

Rotation

Compute Rotation

When on, nParticles rotate on a per-particle basis after they collide or self-collide. Compute Rotation also creates Rotation PP and Angular Velocity PP per-particle attributes on the nParticleShape node.

You can use Rotation PP to rotate instanced geometry on a per-particle basis. Rotation PP and Angular Velocity PP can be used with an expression to add and control per-particle rotations.

Rotation Friction

Sets the amount of friction that is applied to particles during collision or self-collision. Increasing Rotation Friction increases the tendency of particles to rotate. When set to 0, particles do not rotate.

You can add Rotation Friction PP as a dynamic attribute and use it to control rotations in an expression.

Rotation Damp

Specifies the amount of damping applied to the nParticle's rotational velocity. Increasing Rotation Damp causes particle rotation to slow down after collision or self collision. When set to 0, no damping is applied to the rotation, causing the particles to rotate forever if no collisions or self collisions occur.

You can add Rotation Damp PP as a dynamic attribute and use is to control rotations in an expression.

Wind Field Generation

Air Push Distance

Specifies the distance over which the wind created by the motion of the current nParticle object affects nCloth objects or other nParticle objects in the same Nucleus system. The motion of the current nParticle object determines the direction of the wind.

When Air Push Distance is 0, no wind is generated by the motion of the current nParticles. When Air Push Distance is greater than 0, the wind created by the motion of the current nParticle object affects nCloth or other nParticle objects in the same Nucleus system. The higher the Air Push Distance, the greater the distance over which the wind created by the motion of the current nParticle object affects nCloth or other nParticle objects in the same Nucleus system.

Note

• We recommend that you do not use Wind Shadow Distance and Air Push Distance together.
• Air Push Distance is more processor-intensive than Wind Shadow Distance.
• The effect of Air Push Distance is relative to the wind velocity, so a stationary object will slow down the wind within the push distance.

Air Push Vorticity

Specifies the amount of circulation or rotation in the flow of air being pushed by the current nParticle object, as well as the amount of curl in the flow of wind created by the motion of the current nParticle object. Air Push Vorticity changes the direction of the wind created by the motion of the current nParticle object.

Air Push Vorticity only affect’s your nParticles when Air Push Distance is greater than 0.

Wind Shadow Distance

Specifies the distance over which the current nParticle object blocks the dynamic wind of its Nucleus system from other nParticle, nCloth, and passive objects in its system.

When Wind Shadow Distancee is 0, no wind is blocked by the current nParticle object. When Wind Shadow Distance is greater than 0, the dynamic wind of its Nucleus system is blocked by the current nParticle object. The higher the Wind Shadow Distance, the greater the distance for which the current nParticle object blocks the dynamic wind of its Nucleus system.

Wind Shadow Diffusion

Specifies the amount the dynamic wind curls around the current nParticle object as it blocks the dynamic wind of its Nucleus system.

Wind Self Shadow

When on, the current nParticle object blocks the dynamic wind of its Nucleus system from affecting itself.

Liquid Simulation

Enable Liquid Simulation

When on, Liquid Simulation properties are added to the nParticle object. See Liquid Simulations.

Incompressibility

Specifies the amount liquid nParticles resist compression. For water-like liquids, use low values. Increasing Substeps on the nucleus node magnifies the affect of Incompressibility.

Rest Density

Sets the arrangement of nParticles in the liquid when the nParticle object is at rest. A Rest Density of 2 specifies that, when the nParticles are settled, on average, there would be 2 nParticles overlapping at any point. A value of 2.0 provides good results for most liquids.

Liquid Radius Scale

Specifies the amount of overlap of nParticles based on nParticle Radius. Lower values increase overlap between nParticles. A value 0.5 provides good results for most liquids.

Viscosity

Viscosity represents the resistance of the liquid to flow, or how thick, and non-liquid the material is. When this value is high, the liquid flows like tar. When this value is small, the liquid flows more like water. For example, a value of 0.01 produces water-like liquids. For more viscous liquids, use a value of 0.1.

Increasing Substeps on the nucleus node magnifies the affect of Viscosity.

Surface Tension

Specifies the amount of surface tension applied to liquid nParticles. Surface Tension is an attractive force that creates contracting and expanding behavior on the surface of a liquid nParticle object as it moves. The effects of Surface Tension are intended to add realistic surface tension to your nParticle liquid simulations.

The higher the Surface Tension values, the greater tendency nParticles have to attract one another, which causes the overall surface area of the nParticle object to become smaller and more uniformly covered.

Surface Tension affects the behavior of all nParticles belonging to the object, not just those that are visible at the surface of the liquid effect.

Output Mesh

Output Mesh attributes allow you to control the size, smoothness, and dynamic characteristics of Blobby Surface nParticle objects when they are converted to polygon meshes. To see the effects of Output Mesh settings, you must first convert your nParticle object to a polygon mesh by selecting Modify > Convert > nParticles to Polygons. nParticles must be either created or emitted into the scene to be converted to polygons. nParticles emitted after the conversion will continue to add to the size and overall appearance of the nParticle output mesh. Output Mesh attributes are applicable all Particle Render Type nParticles. However, the nParticle output mesh always creates an iso-surface, which is based on nParticle Radius and Threshold.

Threshold

Determines the smoothness of the surface created by overlapping Blobby Surface nParticles. Threshold is based on the overall density of overlapping nParticles. Each nParticle has a density of 1 at its center, which then falls off to a value of 0 at the nParticle's edge.

Blobby Radius Scale

Specifies the amount nParticle Radius is scaled to create an appropriately smooth surface on Blobby Surface nParticles. Increasing Blobby Scale Radius does not affect nParticle Radius, meaning that nParticles can overlap due to Blobby Scale Radius without affecting their dynamic behavior. Increasing Blobby Scale Radius and Threshold together create smooth surfaces on nParticle output meshes.

Motion Streak

Motion Streak elongates individual nParticles based on the direction of nParticle motion, as well as the distance the nParticle travels in one time step. When Motion Streak is 0, nParticles are round. When Motion Streak is 1, nParticles are elongated to a length that is equal to the distance travelled in one time step. Motion Streak applies only to nParticles converted to nParticle output meshes. Motion Streak is useful for creating a motion blur type of effect, and for shaping the flow of Liquid Simulation effects.

Mesh Triangle Size

Determines the size of the triangles used to create the nParticle output mesh. Small Mesh Triangle Size produces high resolution output meshes with smoother surfaces. Small triangles take more computing resources and time to simulate. Mesh Triangle Size can be affected if the particle system bounds are very large relative to the set Mesh Triangle Size. See Max Triangle Resolution.

Max Triangle Resolution

Specifies the grid size that is used to create the output mesh. Max Triangle Resolution clamps the resolution of the voxel grid used in generating the nParticle output mesh's triangles. If the grid size required to create an nParticle mesh exceed the Max Triangle Resolution value, the output Mesh Triangle Size automatically increases to compensate for increasing size of the mesh.

Mesh Smoothing Iterations

Specifies the amount of smoothing applied to the nParticle output mesh. Smooth iterations increase the lengths of the triangle edges, making the topology more uniform, generating a smoother iso-surface. The smoothness of your output mesh increases with increased Mesh Smoothing Iterations values, however, calculation time also increases.

Color Per Vertex

When on, color per-vertex data is generated when you convert an nParticle object to an output mesh. Color per-vertex data is derived from the nParticle object's per-particle color values. The data is color set data and can be applied to the nParticle output mesh like other color set data.

Opacity Per Vertex

When on, opacity per-vertex data is generated when you convert an nParticle object to an output mesh. Opacity per-vertex data is derived from the nParticle object's per-particle opacity values. The data is color set data and can be applied to the nParticle output mesh like other color set data.

Incandescence Per Vertex

When on, incandescence per-vertex data is generated when you convert an nParticle object to an output mesh. Incandescence per-vertex data is derived from the nParticle object's per-particle incandescence values. The data is color set data and can be applied to the nParticle output mesh like other color set data.

Velocity Per Vertex

When on, velocity per-vertex data is generated when you convert an nParticle object to an output mesh. Velocity per vertex is derived from the internal mapping of nParticle velocity values to R, G, and B color values. You can use velocity per-vertex data to create motion blur when the mesh is rendered using mental ray for Maya renderer.

Velocity per-vertex data is passed to the output mesh through the polySurfaceShape node's color set named Motion Vector Color Set. By default this color set uses the velocityPV data generated from the nParticle object.

Uvw Per Vertex

When on, UVW texture coordinates are generated when you convert an nParticle object to a polygon mesh. The texture coordinates let you map a texture to the surface of your output mesh. See nParticle output meshes.

You may need modify the meshes' UVs to get the desired placement of the texture on the mesh. You can view and edit UVs using the UV Texture Editor. For more information about UVs, see Introduction to UV mapping and UV Texture Editor reference in the Modeling guide.

Use Gradient Normals

When on, user normals are created for the output mesh. The normals are based on the direction of the opacity gradient within the particle density. This can improve the appearance and smoothness of the nParticle output mesh, particularly in areas of the mesh that have thin triangles. This setting only affects the output nParticle mesh and not volume nParticle renders.

Caching

Specifies the simulation data that will be saved to a server or local hard drive when the current nParticle object is nCached.

Post Cache Ramp Evaluation

Specifies how ramp attribute data is evaluated. When on, the ramp output is re-evaluated using the cached input attribute rather than the cached data. This attribute is off by default.

If you turn off Post Cache Ramp Evaluation, you need to scrub your simulation before ramp attribute data is read from the cache again.

Memory Cache

When turned on, the motion your nParticle object is saved to memory (not to disk). If you cache data in memory for emitted nParticles, and then later change the rate or another attribute of the emitter or emitted nParticles, you must disable the cache to see the effect of the attribute change.

Emission Attributes

Max Count

Contains the maximum count of particles this shape will allow. If some particles die off, new particles will again be accepted up to the max count, and so on.

Level Of Detail

This attribute is currently only used to scale the amount of emission to be used for quick motion tests without having to change emitter values. This attribute affects only emitted particles.

Inherit Factor

Contains the fraction of emitter velocity that particles emitted into this object inherit.

Emission In World

This boolean attribute tells the particle object to assume that particles created from emission are in world space, and to transform them into object space before adding them to the particle array. This makes the particles respond as if they were in the same space as the emitter when they are in some non-identity hierarchy.

Die on Emission Volume Exit

When this boolean attribute is set to true, if the particles were emitted from a volume, they die when they exit that volume. By default, this attribute is set to false.

Emission Overlap Pruning

Removes newly emitted nParticles before they appear in the simulation based how much they will overlap with existing nParticles. This value scales the collision radius used to determine overlap. A value of 1.0 it guarantees no self collisions with other particles on emission.

Shading

Particle Render Type

This attribute specifies the rendering method for the particles.

	Rendered with software renderer	Rendered with hardware renderer	Rendered with mental ray renderer
MultiPoint
MultiStreak
Numeric
Points
Spheres
Sprites
Streak
Blobby Surface
Cloud
Tube

Depth Sort

This boolean attribute toggles depth sorting of particles for rendering on or off. By default, it is set to false (off).

Threshold

Determines the smoothness of the surface created by overlapping Blobby Surface nParticles. Threshold is based on the overall density of overlapping nParticles. Each nParticle has a density of 1 at its center, which then falls off to a value of 0 at the nParticle's edge.

Opacity

Sets the overall nParticle opacity.

Per Particle Attributes

See Set attributes on a per particle basis and Per particle and per object attributes.

Details on particle expressions can be found in the MEL and Expressions book.

Add Dynamic Attributes

See Add custom attributes.

Goal Weights and Objects

See Goal Weights and Objects

Instancer (Geometry Replacement)

See Instancer (Geometry Replacement)

Sprite Attributes

See Sprite Attributes

Render Stats

Render Stats are accessible from any object’s Attribute Editor.

• Render Stats

mental ray

See forAbout the mental ray for Maya renderer more information.