|On this page|
The Point Velocity SOP provides a simple interface to compute and manipulate
the velocity attribute,
v, of a geometry’s points. The node includes
functionality to robustly compute velocity from time-dependent deformation of
the incoming geometry, as well as several ways to generate and composite noise
on top of it.
The order of tabs corresponds to the order in which their corresponding operations are performed (from left to right). When enabled, Add Velocity modifier is applied last.
Geometry whose point velocities to manipulate.
Only points in this group will be affected by this node.
When enabled, this vector is added to every point’s velocity.
Controls how the velocity point attribute is initialized.
Compute from Deformation
Point velocities are deduced from their time-dependent motion.
The incoming point velocities are kept; if the input geometry does not contain a velocity point attribute, it is created and initialized to zero.
The given Default Value is written to each point’s
Velocities are initialized using the value of the given point attribute.
Velocities get set to this value; only available when Initialization mode is Set Value.
Frame offset used for computing point velocities from deformation.
If Velocity Approximation is set to Central Difference, the geometries used are offset forward and backward by Frame Sample.
Evaluate Within Frame Range
Enabling this option ensures that the geometry is not evaluated outside of the provided Frame Range.
When Evaluate Within Frame Range is enabled, the node ensures that the input geometry is not evaluated outside of this range.
Finite difference method to use for computing velocities from deformation.
Approximates velocity by considering the difference in particle positions from the current frame and the frame offset backward by Frame Sample.
Approximates velocity by considering the difference in particle positions from the current frame offset forward and backward by Frame Sample.
Approximates velocity by considering the difference in particle positions from the current frame offset forward by Frame Sample and the current frame itself.
If Evaluate Within Frame Range is enabled and one of the frame samples lies outside the specified Frame Range, this node will try to use an alternate approximation scheme.
When this option is enabled, this node will also approximate point accelerations. This is useful for rendering curved trajectories with acceleration motion blur.
The calculated accelerations will only be non-zero if Velocity Approximation is set to Central Difference.
The computed acceleration will be stored in this point attribute.
Compute Angular Velocity
Enabling this option will use the difference in orientations to compute the
angular velocity (stored in the
w point attribute).
Match by Attribute
When this option is enabled, points on successive frames will be identified by using the value of the provided attribute rather than the point number.
Attribute to Match
Name of the integer or string point attribute to use for matching successive frames (when Match by Attribute is enabled).
Name of the point attribute to use for initializing velocities. Only available when Initialization is set to From Attribute.
Attribute corresponding to Attribute Name is multiplied by this value to get the initial point velocities.
Add Curl Noise
Adds divergence-free curl noise to point velocities.
If this option is turned on, produced noise will vary with time.
Controls the amount of added curl noise.
Time rate of change of the noise pattern is inversely proportional to Pulse Duration; only available when Animated is enabled.
Controls base feature size of the generated noise.
Feature size along each axis is governed by the product of Swirl Size with the applicable component of this parameter.
Offset within the evaluated noise field. Can be used as a seed to modify the noise values without affecting the overall look of the pattern.
Controls influence falloff for each successive noise layer.
Specifies the number of composited noise layers.
Noise for each point is produced by sampling a volumetric field using the
value of this vector attribute. If this parameter is set to
applied noise pattern will vary based on the motion of the points. If this
is undesirable, a
rest attribute can be added to the input geometry and
its value used instead.
Add Object Motion
Adds the velocity of an animated object-level node to point velocities.
The object node to extract a transform from.
Before being added to point velocities, the object velocity is scaled by this amount.
Frame offset used for computing the object’s velocity.
If Velocity Approximation is set to
Central Difference, the
object transforms used are offset forward and backward by Frame
Finite difference method to use for computing the object’s velocity.
Approximates velocity by considering the difference in object’s transformations from the current frame and the frame offset backward by Frame Sample.
Approximates velocity by considering the difference in object’s transformations from the current frame offset forward and backward by Frame Sample.
Approximates velocity by considering the difference in object’s transformations from the current frame offset forward by Frame Sample and the current frame itself.
Modify point velocities with conical noise.
Conical noise is not spatially coherent, nor does it continuously depend on the seed values.
In Add mode, each point’s velocity is offset by a random vector, which falls within the defined cone. In Rotate mode, each point’s velocity is randomly jittered within a cone of the specified size (without affecting speed).
Controls the cone height (and the amount of added conical noise) when Mode is set to Add.
Controls the cone width.
The cone opens in this direction; only available when Mode is set to Add.
When enabled, value of this vector point attribute is used to control the cone orientation for each point, instead of the global Direction parameter; only available when Mode is set to Add.
If the referenced point attribute does not exist or is zero, the global Direction vector is used.
When enabled, the randomly generated vector is biased towards the center of the cone (for positive values) or the edge of the cone (for negative values).
Value of this parameter is used to seed the random number generator. The generated noise can be altered by changing the seed.
When enabled, the value of this attribute is used for seeding the random vector for each point instead of the point number; this enables consistent noise generation when deleting points.