Tracer is an advanced particle multiplication operator. This particle generator allows You to increase the amount of particles in any simulation without actually adding extra load to the solver. Particles are created “outside” of the main simulation and once created, those extra particles are “dragged” along with their neighbors. A simple low particle count simulation can easily be turned into a million particle simulation that looks as if it was created with a much higher initial particle count.

Tracer particles can either be generated procedurally, on the fly, or they can be supplied through the means of particle groups. 

On - (Bool) This input data stream determines whether the operator is considered 'on' or 'off.' You can connect other operators to this input channel such as a Bool Helper to activate/deactivate the whole operator.

Time - (Time) This input data stream is used to define the local time for the operator when the user wants to override the default system time.

All other operator input options represent the identical UI controls and are explained in detail in the below rollout menu section.

*Born Particle - (Particle) This output data stream sends particle data for newly created particles to other operators. Every particle birth will activate all rules connected to this particle data stream. As a result , this can be used to directly assign a value to the particle.

*Source Particle - (Particle) This output data stream sends particle data of the original (source) particles to other operators. Every particle will activate all rules connected to this particle data stream. As a result , this can be used to directly assign any value to the particle.

Source - defines the source particles to be used as a “tracking” and creation reference for tracer particles.

Include Sub Groups - check this option to include particle Sub Groups for the source particles.

Tracer -

Include Sub Groups - check this option to include particle Sub Groups for the tracer particles.

Create Tracer - check this option to automatically generate tracer particles based on the source particle input. If this option is not checked, existing particles supplied in the selected Tracers particle group will be used. There are various options to create tracers.

At Start - when checked, tracer particles will be created at Frame 0 or at the relevant simulation start frame.

At Birth - check this option to create tracer particles at birth of any source particle.

At Enter Group - this option will create tracer particles when new particles enter the source particle group.

Radius - defines radius around the source particle were the tracer particles are randomly created.

Factor - sets a multiplication value to define the amount of tracer particles created for each source particle.

Clip Volume - check this option to delete all “outside” tracer particles when they are created. This feature creates a volume around the source particle cloud and this bounding volume is used to decide if a particle lies outside of the original particle cloud, and then it gets deleted.
This option is best used to create flat surfaces bny avoiding tracer particles to be created outside the original particle cloud's surface.

Surface Radius - sets the distance from the source particle to be used to create the hull around the source particles.

Cell Size - sets the raster size in world units for the bounding volume. The finer this volume is created the closer it resembles the real hull of the source particle cloud.

Iso Value - defines the ISO value to be used for the hull creation. ISO of 0 means the exact surface of the bounding volume.

Filter - the bounding, or hull volume data can be filtered by various functions.

Box - select this option to use a box filter.

Gaussian - when selected, a gaussian filter is used.

Mean Curvature - check this option.to use a Mean Curvature filter method.

Laplacian - use this option to filter the hull data with a Laplacian filter method.

Iteration - sets the amount of filter passes to be used.

Show - for debugging purposes the bounding volume can be visualized in the 3ds max viewport. There are multiple options to visualize the clipping volume dimensions. There are None, Source Bounding Box and Clip Volume.

Transfer Data - check this option to transfer all essential particle data over to the newly created tracer particles. The following parameters will be transfered: Mass, Size and Data Channels. Note, due to the volume nature of this functions either the average collected value within the radius will be used or the nearest particle will be used to set the newly created tracer particle.

Radius - defines the search radius for the particle paramter transfer.

Type - parameter transfer can happen in 2 ways. Either by using the average values of all source particles within the radius found or by just picking the nearest source particle to transfer the data.

Show - to visualize the volume or grid resolution used to transfer the data, choose the Grid option.

Trace - check this option to trace or track the source particles and move the tracer particles along. The velocity of the source particles will be used to define the speed of the tracers.

Radius - sets the search radius for the tracer particles to look for source particles. The Type option defines the method of how to find the source particles.

Type - there are several interpolation types to define the velocties that will be used to move the tracer particles.

Nearest - check this option to use the velocity of the closest source particle to moev a tracer particle.

Tri LInear - this option will interpolate velocities found in the source velocity grid to be used by the tracer particle. This usually results in a smoother tracking/following.

Quadratic Linear - this option will interpolate velocities found in the source velocity grid to be used by the tracer particle. This usually results in a smoother tracking/following. This option is the slowest but usually results in the most natural outcome.

Out Of - tracers can become “disconnected” from a source particle. This setting offers multiple options to handle such situations.

Original Velocity - when a tracer particle becomes disconnected, its original velocity will be maintained.

Zero Velocity - when a tracer particle becomes disconnected, its velocity will be set to zero.

Kill Particle - when a tracer particle becomes disconnected, its velocity will be set to zero.

Show - lets you visualize the Grid, used for the interpolation of velocities.Keep in mind, to update the Grid preview a simulation step might be necessary.