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This operator calculates and applies forces necessary to make particles orbit around a center-point.
You can use the second input to specify the center particles, or use the parameters on the Center tab to choose a group in the first input that will specify the center.
The Center Type parameter on the Center tab let you choose how the center works:
You can specify the center with 3D coordinates.
The "center" can be a computed point based on the center particles (the spatial center of the leader particles, the center of mass, or the center of density).
Each particle in the center stream can be the center for individual particles from the satellite stream. Houdini can automatically assign satellites to centers, or you can set a
orbitattribute on particles to determine which center they will orbit. Use the Property POP to set the orbit-related attributes on particles.
Orbit works similarly to the Follow POP, which makes particles follow a leader or leaders.
To help visualize the effect of this operator, turn on the template flag to view the acceleration guides.
This operator modifies the following attribute:
Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.
Note that this is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.
Use the value of the Axis parameter below instead of the orbit axis attribute if it exists on a particle.
A vector to use as the orbit axis, when Override axis is on.
Use the value of the Radius parameter below instead of the orbit radius attribute if it exists on a particle.
Radius of orbit (in units), when Override Radius is on.
Use the value of the Speed parameter below instead of the orbit speed attribute if it exists on a particle.
Speed of the orbit (in RPM), when Override Speed is on.
Scaling factor that controls how fast particles move into their proper orbit from their initial position.
Subset of points from the first input to act as centers. You can use this parameter instead of connecting the second (Center) input.
Specifies what the particles orbit around.
Particle Spatial Center
The center of the box bounding the center particles.
Particle Center of Mass
The center of mass of the center particles.
Particle Density Center
The center of mass, with all particles having equal mass.
Use the coordinates in each particle’s orbit center attribute (or the coordinates in the Center Point parameter below if Override Center Point is on).
Each orbiting particle orbits a center particle. If you
on the follower particles, they will use the attribute
to decide which leader to follow (using the Orbit
index parameter below). Otherwise, Houdini will
automatically assign followers to leaders.
Override Center Point
Use the value of the Center Point parameter below instead of the orbit center attribute if it exists on a particle, when Center Type is "Center point".
Point to orbit around, when Center type is "Center point" and Override Center Point is on.
(Available when Center type is "Individual Particles")
Controls how the node interprets the
attribute on particles to assign satellites to centers.
Particles that do not have
orbit attributes are assigned
to leaders automatically, using particle order to refer to a
orbit attribute on the satellite particles refers
to the particle ID of the center they should orbit.
orbit attribute on the follower particles refers
to the position of the center particle in the list of
particles. In a particle system where leader particles
are dying and points are being reused, this could mean
the centers change as particles die (even if they are
not in the center stream).
The particles that will be made to orbit the center or centers.
The particles that define the center(s) to orbit. If you do not connect this input, you must set the Center Group parameter on the Center tab.
Standard POP local variables
The seconds a particle in the template has been alive.
AX AY AZ
Acceleration of the particle.
BBX BBY BBZ
The point’s relative position in the bounding box.
Point is dead.
Processing iteration number.
A collision for this particle was detected (for example, by the Collision POP) during the processing of this timestep (that is, this iteration of the particle simulation). This variable is cleared at the beginning of each timestep. Note that the collision POP actually detects any collisions which would have occurred the during the previous frame.
Percent of total life used (from 0 to 1).
Expected lifetime of particle.
MAPU MAPV MAPW
Point or vertex texture coordinates.
Total number of points.
Total number of points in source group.
NX NY NZ
The point number of the currently processed point. The
PT is not constant like
ID; it changes based on the number of points.
RESTX RESTY RESTZ
The rest position.
The sliding state of the particle.
Elasticity of a point.
Point is stopped.
1 if particle is stuck to a collision object.
TX TY TZ
Surface UV values.
VX VY VZ
Point spline weight.
Distance from particle to last collision.
HCR HCG HCB
Diffuse color at the collision point on the surface the particle collided with.
ID for last collision. You can control how this attribute is set in the Collision or Limit POP to help distinguish types of collisions.
The time at which the last collision occurred.
The texture map UV coordinates for the surface location where the last collision occurred.
HNX HNY HNZ
The normal at the surface location where the last collision occurred.
HTX HTY HTZ
World space position of the last collision.
The UV coordinates for the surface location where the last collision occurred.
Number of times the particle has collided.
Added by Color POP
Point or vertex alpha value.
CR CG CB
Diffuse point or vertex color.
Added by Property POP
Charge of the particle.
Point is clinging to geometry.
Leader to follow.
SCALEX SCALEY SCALEZ
Added by Proximity POP
Either the point number or id of the particle nearest to this one.
The distance to the nearest particle.
The number of particles within a specified proximity to this particle.
Added by Rotation POP
ROTX ROTY ROTZ
Added by Source POP
ID number, which always remains constant.
Original Source point was birthed from.
Parent’s ID Number.
Added by Speed Limit POP
Added by Sprite POP
Sprite rotation around view axis (in degrees).
Texture coordinate of sprite’s lower-left corner.
Size of sprite in texture space.
Controlled by Suppress Rule POP
Suppress default position rule.
Suppress default velocity rule.
Suppress default up-vector rule.
Suppress default aging rule.
1 if particle is suppressing its default rotation rule.
1 if particle is suppressing its default angular velocity rule.
Added by Up Vector POP
PVX PVY PVZ
UPX UPY UPZ
Absolute speed of particle.