Unite Close Vertices finds groups of mesh vertices that lie closer to each other than a given distance and replaces each group with one vertex. You need it when a mesh has open seams: two edges that should be joined run next to each other, each with its own, almost identical vertices.
Such seams appear, for example, in STL files exported from CAD, when neighboring faces of a part are triangulated separately, and after combining several mesh parts. A seam looks closed, but MeshInspector counts it as a hole, and the parts on both sides can even be separate components.
When MeshInspector opens an STL file, vertices with exactly the same coordinates are already merged. A seam stays open when the coordinates differ slightly, and this is what Unite Close Vertices fixes. Mesh Healer also unites boundary vertices with exactly the same position before it repairs Holes or Disconnected Parts, but it does not unite vertices that are only close.
Unite close vertices
- Select the mesh.
- On the Mesh Repair tab, click Unite Close Vertices.
- Set Close distance. Keep Only boundary vertices on.
- Click Apply (or press Enter).
The panel closes, and the number of united vertices is written to the log, for example "661 vertices were united". To undo, press Ctrl+Z (Cmd+Z on macOS).
Settings
| Setting | What it does | Default |
|---|---|---|
| Close distance | Vertices located closer than this distance are united. | 0 |
| Only boundary vertices | Only vertices on a boundary (the edge of a hole) can be united. Inner vertices stay, even if they are close to each other. | On |
Which Close distance to choose
- The gap in a seam is usually much smaller than any edge of the mesh. Start with a small value, check the Holes and Components rows in the Information panel after Apply, and increase the value only if the seam is still open.
- Keep Close distance well below the Avg Edge Length shown in the Information panel. All vertices closer than this distance are merged, including both ends of real short edges, and small details collapse.
- Keep Only boundary vertices on. Seams are boundaries, so you rarely need to unite inner vertices.
- To see the problem spots before you unite, use Select Twin Edges, which finds pairs of vertices located very close to each other, and Select Short Edges, which selects all edges not longer than a given value.
Example: an open seam in a CAD part
We took the CAD part from our demo files and moved one half of it by 0.0005 mm to reproduce an open seam. MeshInspector showed 2 holes and 2 components, while the original part has none. The average edge length of the part is 5.9 mm.
With Close distance 0.001 mm and Only boundary vertices on, Unite Close Vertices united 661 vertices. The seam closed: no holes, 1 component, and 39,730 vertices, the same as in the original part.
A too large value destroys the mesh. With Close distance 2 mm and Only boundary vertices off, the same closed part lost most of its geometry: 38,419 vertices were united, 79,516 triangles became 2,661, and the part got 18 holes.
Example: a jagged scan boundary
On a 3D scan, several vertices along an open boundary can lie very close to each other and form an uneven, jagged edge. Run Unite Close Vertices with Only boundary vertices on and a small Close distance: nearby boundary vertices are merged, and the edge becomes cleaner and more continuous.
