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Manual Segmentation

In one sentence: Paint mesh faces interactively with a brush to define user-labelled regions when automatic segmentation is insufficient.

Overview

Workbench: Reverse Engineering
Menu: Reverse Engineering → Segmentation → Manual Segmentation…
Shortcut: none

Opens a task panel with a brush tool and a segment list. You select a segment label and paint faces onto it by dragging the mouse over the mesh in the 3-D view. Each segment becomes a separate Mesh::Feature in a "Segments" group.

Intuition

Think of it like painting by numbers, but you decide where each colour goes. You have a blank mesh and a list of labelled buckets (segments). You pick a bucket and drag your brush over the faces you want to assign to it. When you are done, each painted region becomes its own sub-mesh.

Use this when the automatic Mesh Segmentation gets the boundaries wrong — for example where two surface types blend smoothly into each other and the curvature threshold is ambiguous.

When to use it

  • Automatic Mesh Segmentation produces wrong segment boundaries and you need to correct them.
  • The mesh has ambiguous curvature transitions that no threshold setting can separate correctly.
  • You have domain knowledge about the part geometry and can paint the correct boundaries by hand.

When NOT to use it

  • Large meshes with clear geometric primitives — use Mesh Segmentation for automatic classification; it is faster and more consistent.
  • Already-split meshes — use From Components.

Step-by-step

  1. Choose Reverse Engineering → Segmentation → Manual Segmentation….
  2. In the task panel:
  3. Select the mesh from the Shapes drop-down.
  4. Click Add under the Segments list to create a new segment label.
  5. Select the segment you want to paint into.
  6. Left-click and drag over mesh faces in the 3-D view to paint them onto the selected segment.
  7. Right-click and drag to remove faces from the current segment.
  8. Scroll the mouse wheel to change the brush size.
  9. Repeat steps 3–6 for each region.
  10. Click OK. FreeCAD creates a "Segments" group with one Mesh::Feature per painted segment.

Parameters (brush controls)

Control Action
Left-click drag Add faces to the current segment
Right-click drag Remove faces from the current segment
Scroll wheel Increase / decrease brush radius

Common mistakes and pitfalls

Painted faces belong to the wrong segment

Cause: The segment selection in the list did not change before painting.
Fix: Click the correct segment in the Segments list before painting. The active segment should be highlighted.

Brush paints through the mesh to the far side

Cause: The brush applies to all faces projected under the cursor, including faces on the back of the mesh.
Fix: Rotate to a view where only the intended faces are facing the camera, or use the zoom to restrict the field of view.

Python API

Manual Segmentation is an interactive-only tool. Access the results after creation:

import FreeCAD as App

doc = App.ActiveDocument
segs_group = doc.getObject("Segments")   # or "Segments MyMesh"
if segs_group:
    for obj in segs_group.Group:
        print(obj.Name, "—", obj.Mesh.CountFacets, "faces")

See also