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.
/result - How to construct the trail geometry.
- Preserve Original - Preserves the original geometry.
- Connect as Mesh - Connects the resulting points as a mesh.
- Connect as Polygons - Connects the resulting points as polygons.
- Compute Velocity - As the points move faster, corresponding velocity attributes are computed.
/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.
/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 - The number of frames to keep cached in available memory.
/clear - Resets the cache memory buffer.
Evaluate Within Frame Range
/evalframe - This option specifies that the Trail SOP will only evaluate, or cook, within the current frame range (
$FEND). If this option is not enabled, the SOP can evaluate prior to the start frame.
/surftype - This option is used to select the type of surface, when using a Mesh Primitive Type.
- Rows - Creates horizontal lines.
- Columns - Creates vertical lines.
- Rows & Cols - Both Rows and Columns. Looks like Quads in wire frame display, but all polygons are open (if the primitive type is polygon).
- Triangles - Build the grid with Triangles.
- Quadrilaterals - Generates sides composed of quadrilaterals (default).
- Alternating Triangles - Generates triangles that are opposed; similar to the Triangles option.
/close - When selected, closes the rows in the output selection.
/velscale - Scales the velocity by a specific value when Compute Velocity is selected.
The particles thrown off the end-most points recieve a higher velocity than those close to the root of the L-system:
Temporal modelling with the Trail SOP:
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: