Trail SOP

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The Trail SOP takes an input SOP and makes a trail of each point of the input SOP over the past several frames, and connects the trails in different ways. It will generate trails of any input geometry, whether it is a cube translating, a deforming surface, or particles. This is useful for multi-frame ghosting effects and temporal modelling.

When using a Particle SOP or Spring SOP as input, it is important to keep the trail increment to integer values. Otherwise, the trail will not work well.


Result Type result - - How to construct the trail geometry.

  • Preserve Original preserve - Preserves the original geometry.
  • Connect as Mesh mesh - Connects the resulting points as a mesh.
  • Connect as Polygons poly - Connects the resulting points as polygons.
  • Compute velocity velocity - As the points move faster, corresponding velocity attributes are computed.

Accurate Timing accurate -

Trail Length length - This sets the length of the trail by establishing the maximum number of frames for the Trail SOP to use, i.e. a Trail Length of 25will connect the geometry from the previous twenty-five frames.

Trail Increment inc - This will skip the given number of frames to build a trail with fewer points in it, but the same length. This will lower the resolution of the trail by reducing the number of points in the trail. This is better for ghosting when using Preserve Original. If you set the Increment to 2 or more, you will see the same length trail, but fewer copies of the geometry.

Cache Size cache - The number of frames to keep cached in available memory.

Evaluate Within Frame Range evalframe - This option specifies that the Trail SOP will only evaluate, or cook, within the current frame range ($FSTART, $FEND). If this option is not enabled, the SOP can evaluate prior to the start frame.

Connectivity surftype - - This option is used to select the type of surface, when using a Mesh Primitive Type.

  • Rows rows - Creates horizontal lines.
  • Columns cols - Creates vertical lines.
  • Rows and Columns rowcol - Both Rows and Columns. Looks like Quads in wire frame display, but all polygons are open (if the primitive type is polygon).
  • Triangles triangles - Build the grid with Triangles.
  • Quadrilaterals quads - Generates sides composed of quadrilaterals (default).
  • Alternating Triangles alttriangles - Generates triangles that are opposed; similar to the Triangles option.

Close Rows close - When selected, closes the rows in the output selection.

Velocity Scale velscale - Scales the velocity by a specific value when Compute Velocity is selected.  

Reset reset -

Reset Pulse resetpulse -


Velocity Computation

The particles thrown off the end-most points recieve a higher velocity than those close to the root of the L-system:


Temporal Modelling

Temporal modelling with the Trail SOP:

TrailSOP TemporalSculpt.gif

The corners of a translated and rotated cube are used as a source for the Trail SOP with a Trail Length of 50 frames connected by Columns:


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An Operator Family that reads, creates and modifies 3D polygons, curves, NURBS surfaces, spheres, meatballs and other 3D surface data.

A surface type in SOPs including polygon, curve (NURBS and Bezier), patch (NURBS and Bezier) and other shapes like sphere, tube, and metaball. Points and Primitives are part of the Geometry Detail, which is a part of a SOP.

To pulse a parameter is to send it a signal from a CHOP or python or a mouse click that causes a new action to occur immediately. A pulse from a CHOP is typically a 0 to 1 to 0 signal in a channel, and a pulse via python is via a .pulse() call on a pulse-type parameter, such as Reset in a Speed CHOP.