TYPE: POP
TITLE: Follow POP

The Follow POP applies forces on the particles so that they 
follow a leader. To help visualize the effect of this operator, 
turn on the template flag to view the acceleration guides.

This POP modifies the following attributes: accel.

Parameters:
    Activation                  - Turns the POP on and off	/activate
    Source Group                - Subset of points to act as followers
Follow
    Behavior                    - The type of following behavior
        Normal Follow           - Force applied is such that for particles
                                  of unit mass, the velocity for the
                                  next frame will be towards the specified
                                  position with a speed equal to that of
                                  the leader.
        Accelerating Follow     - Force is a unit force towards the
                                  leader. Note this will cause the particle 
                                  speed to continually increase.
    Minimum Distance            - Particles closer than this will be brought
                                  rapidly to a stop.		/mindistance
    Maximum Distance            - If non-zero, particles further than this
                                  distance from followed point will NOT
                                  follow.			/maxdistance
    Ambient Speed               - If the speed of the leader falls below this
                                  speed, the ambient speed is used as the 
                                  target speed instead.		/ambspeed
    Attract Distance            - If the distance to the leader is
                                  less than this, the force is repulsive.
                                  Otherwise, it is attractive.	/attdistance
    Predict Intercept           - If toggled, the particle will try to predict
                                  the leader's direction on the next frame and
                                  head it off.
    Stop At Leader              - Particle comes to a complete stop when it
                                  reaches the leader.
    Scale                       - Multiplier for applied force	/scale
    Speed Scale                 - Multiple of target's speed to use	/sscale
Leader
    Leader Group                - Subset of points to act as leaders
    Leader                      - Specifies what is used as the leader.
        Particle Spatial Center - The center of the box bounding the leader
                                  particles.
        Particle Center of Mass - The center of mass of the leader particles.
        Particle Density Center - Corresponds to the center of mass with all
                                  particles having equal mass.
        Individual Particles    - Each following particle is assigned one
                                  leader particle to follow.
    Follow Index                - How to interpret the follow index
Defaults
    Ignore Mass                 - Ignore particle mass
    Override Mass               - Override particle mass
    Mass                        - Mass to use for override	/mass

Local Variables 
    Overview - The standard local variables are usable in this POP.  Please
               refer to the Houdini manual for more details.
