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Wire From Mesh Boundary

In one sentence: Extract the boundary loops of a mesh as Part wires or a planar face that can be used in subsequent CAD operations.

Overview

Workbench: Reverse Engineering
Menu: Reverse Engineering → Segmentation → Wire From Mesh Boundary…
Shortcut: none

Finds all boundary edge loops of a mesh (edges that have only one adjacent face — the perimeter of any holes or the outer edge of an open mesh) and creates a Part::Feature. If the loops are co-planar, the result is a face; otherwise it is a compound of wires.

Intuition

An open mesh has edges on its perimeter — like the border of a cookie cutter shape. Wire From Mesh Boundary traces all those border edges and converts them into a proper CAD wire (a connected chain of edges) or a face. You can then use that wire in sketches, as a sweep path, or as a boundary edge for surface filling.

When to use it

  • You have an open mesh (e.g. only the top surface of a scanned part) and want to extract the boundary profile as a CAD curve for modelling.
  • You need a closing face to make a mesh watertight for FEM or 3-D printing.
  • You want to reference the mesh perimeter in a Sketcher sketch.

When NOT to use it

  • Watertight, closed meshes — a closed mesh has no boundary edges; the tool will create nothing or report no boundaries found.
  • When you need the full mesh converted to a solid — use Mesh workbench → Convert Mesh to Solid or Part workbench → Shape from Mesh.

Step-by-step

  1. Select one or more Mesh::Feature objects.
  2. Choose Reverse Engineering → Segmentation → Wire From Mesh Boundary….
  3. FreeCAD creates a Part::Feature:
  4. If all boundary loops are co-planar: a face is created.
  5. Otherwise: a compound of wires is created.

Parameters

This tool has no parameter dialog.

Result types

Condition Result
Boundary loops are co-planar Part::Feature with a face (filled)
Boundary loops are non-planar Part::Feature with a compound of wires
No boundary edges found Nothing created

Common mistakes and pitfalls

Produces wires instead of expected face

Cause: The mesh boundary is not planar — it curves in 3-D space, so a flat face cannot fill it.
Fix: Use the resulting wires as boundary curves for the Surface workbench's Filling tool.

No result produced for a closed mesh

Cause: A watertight mesh has no boundary edges — there is nothing to extract.
Fix: Use Poisson Reconstruction or the Mesh workbench's cut and segmentation tools to create an open mesh first.

Python API

# Wire From Mesh Boundary is command-driven:
import FreeCADGui as Gui
Gui.doCommand("Gui.runCommand('Reen_MeshBoundary', 0)")

# Access the result:
import FreeCAD as App
wire_feat = App.ActiveDocument.ActiveObject
print(type(wire_feat.Shape))  # Part.Face or Part.Compound

See also