Post-processing modifies a node’s solved geometry without adding another branch to the scene tree. Each step receives the result of the previous stage, applies one operation, and passes its output forward.

Use the object tree for design structure—primitives, Booleans, groups, and feature relationships. Use post-processing for result-level changes such as mirroring, trimming, offsetting, and shelling. This article follows Constructive Solid Geometry in Rig Cad and Transforms and Reference Frames in Rig Cad.

The examples focus on the ordered stack and four foundational steps: Mirror, Cut Plane, Surface Offset, and Shell.

The stack runs in order

A post-processing stack is evaluated from its first step to its last:

solved node → step 1 → step 2 → final output

Each step operates on the geometry produced immediately before it. Reordering the stack can therefore change topology, dimensions, and even whether a later step succeeds.

Every foundational step has an Enabled option. Disable a step to bypass it without deleting its settings. This is the fastest way to compare the processed and unprocessed result or isolate the step that introduces a failure.

Check compatibility before adding a step

Available steps depend on the node’s dimensionality, path type, and solver.

Compatibility only means the step can run on that representation. The geometry must still support the requested offset, wall thickness, or cut without collapsing or self-intersecting.

Interactive Sandbox
View project
The root contains a prebuilt Mirror → Surface Offset → Shell → Cut Plane stack. Toggle each step in Variables, inspect its settings in Properties, and observe how every stage receives the output above it.
Explore the Post-Processing Stack DemoInteractive Rig Cad editor

Mirror

Mirror uses a plane to keep one side of the input and reflect it across that plane. It is useful when the final result should be symmetric but the source geometry is easier to construct on one side.

The plane is defined by:

  • Origin X, Y, and Z — the plane’s anchor point;
  • Azimuth — its horizontal heading, measured counter-clockwise from +X;
  • Elevation — its vertical angle above the XY plane; and
  • Invert — which side is kept and mirrored.

Place the plane from model dimensions rather than viewport appearance. A centered mirror plane should normally derive its origin from the same variables that position the source feature.

Cut Plane

Cut Plane removes one side of a plane. Use it to trim a result, expose an interior, or create a controlled planar termination.

The plane uses the same origin, azimuth, and elevation controls as Mirror. Offset moves the plane along its normal; positive values move outward and negative values move inward. Invert selects the opposite side to keep.

Cut Plane changes the output geometry. It is not a temporary viewport section. If the cut is only for inspection, use a non-destructive viewing or section tool instead.

Surface Offset

Surface Offset moves a boundary away from or toward the original surface:

  • a positive offset expands the result;
  • a negative offset shrinks it; and
  • an offset of zero leaves the boundary unchanged.

For open 2D paths, the operation creates rounded strokes. Positive offsets on 3D paths create tubes. Mesh Segments controls the resolution around rounded 3D edges or tubes; increase it only when the visible result requires more smoothness.

For 2D profiles, Corner Shape selects round, miter, or square corners. Rounded corners use Corner Segments. Mitered corners use Miter Limit to prevent excessive spikes.

Surface Offset changes the overall boundary. It does not create a controlled wall by itself; use Shell when wall thickness is the design requirement.

Shell

Shell creates a wall around the input surface.

  • Wall Thickness sets the wall size.
  • Wall Position places the wall inside, centered on, or outside the original surface.
  • Offset Method selects CP for speed and preservation of the original surface structure, or Tess for difficult curved surfaces that need closer geometric following. These are Shell algorithm labels; CP here does not refer to the control-point variables used in profile projects.

Mesh and corner controls affect the generated approximation where applicable. Higher segment counts can improve appearance but increase geometry cost.

A shell can fail when the requested thickness exceeds a narrow feature, tight concavity, or local radius. Start with a small thickness, verify the result, and then increase it.

Order changes the result

The same steps can produce different geometry when reordered.

  • Shell → Cut Plane shells the original result and then trims the completed wall.
  • Cut Plane → Shell trims first, so Shell processes the new boundary created by the cut.
  • Surface Offset → Shell changes the reference boundary before wall generation.
  • Shell → Surface Offset offsets the completed shell, including its inner and outer boundaries.

Choose the order from the intended construction, not by trial alone. When a stack fails, disable every step, then re-enable them from top to bottom. The first failing step is where the input or settings need attention.

A focused editor exercise

Use the embedded demo to inspect the prebuilt stack:

  1. Select PostProcessing Demo in Objects and locate its four post-processing steps in Properties.
  2. Toggle mirrorOn off and on. Compare the authored half with the symmetric result.
  3. Toggle offsetOn, then adjust offsetAmount to expand or shrink the boundary.
  4. Toggle shellOn, then change wallThickness within its provided range.
  5. Toggle cutOn, then move cutOffset to reposition the vertical section plane.
  6. Move Shell above Surface Offset and compare the result, then restore the original order.
  7. Reset the article session when finished.

The exercise isolates one stage at a time, then demonstrates that reordering changes the input received by every later step.

Diagnose failures systematically

Symptom Likely cause First check
A step is unavailable Dimensionality, path type, or solver is incompatible Confirm the selected node’s output type
The result disappears after an offset A negative offset collapsed a narrow region Reduce the magnitude
Shell produces gaps or fails Thickness exceeds local feature size Start with a smaller wall thickness
Rounded output is visibly faceted Segment count is too low Increase it gradually
Geometry becomes unnecessarily heavy Segment count is too high Reduce resolution to the lowest acceptable value
Reordering changes the part unexpectedly A later step receives different topology Trace the stack from the first step
A plane acts on the wrong side Plane orientation or Invert is wrong Check origin, azimuth, elevation, and Invert

Next steps

Post-processing should refine a sound model, not replace its design structure. Continue with Mesh Cleanup in Rig Cad: Repair, Remesh, and Simplify Geometry to diagnose topology, rebuild triangle distribution, and control final polygon count.

For smooth field-defined inputs, use Signed Distance Fields: Geometry as a Function. For a focused construction rule that keeps Boolean and SDF cuts robust, use Oversize the Cutter.