Expand Selection adds one layer of triangles around the selected triangles of a mesh. Use it to make a selection a little larger, for example to take in the ragged border around a defect before you delete it. This guide also covers the two tools in its drop-down: Smart Expand, which grows a selection across flat and smooth areas first, and Expand Selected Edges, which grows a selection of edges.
Which tool to use
| Tool | What it adds | Use it to |
|---|---|---|
| Expand Selection | One layer of triangles per click | Grow a selection a little, step by step |
| Smart Expand | Triangles in flat and smooth areas first, then across sharp edges | Fill a flat face or a smooth area up to its sharp edges |
| Expand Selected Edges | One layer of edges per click | Widen a selected edge contour |
| Grow/Shrink Selected | Triangles within a distance in mm | Grow by the same distance on fine and coarse areas |
To make the selection smaller again, use Shrink Selection.
Expand a triangle selection by one layer
- Select triangles on the mesh, for example with Select Primitives.
- Click Select › Expand Selection or press Ctrl+= (Cmd+= on macOS).
- Repeat until the selection is large enough.
The tool works at once, without a panel. Each click adds every triangle that shares an edge with a selected triangle. A layer is as wide as the triangles at the border, so on a fine mesh one click grows the selection only a little. To undo a step, press Ctrl+Z (Cmd+Z on macOS).
Selected edges work as a fence: the selection does not grow across an edge that is selected. The button is unavailable when the mesh has no selected triangles, and when all its triangles are already selected.
Smart Expand
Smart Expand grows a triangle selection over flat and smooth areas first and crosses sharp edges and strongly curved areas last. Use it to select a whole flat face or a smooth area of a part from a few triangles.
- Select a few triangles inside the area you want.
- Open the drop-down arrow next to Expand Selection and choose Smart Expand.
- Drag the Expansion value up. The selection in the viewport changes as you drag.
- Close the panel to keep the result.
| Parameter | What it does | Default |
|---|---|---|
| Expansion | How much to expand the selection: 0% keeps your selection, 100% adds every triangle that can be reached from it | 0% |
The selection grows in order of curvature: the selection fills a flat face before it starts to cross the sharp edge around it. The value is the share of the triangles that the selection can reach. On the part below, a few triangles on the flat face grow to the whole face (3,016 of 12,946 triangles) at 23%; higher values continue across the edges of the face. At 100% the selection covers the whole connected part of the mesh. Selected edges stop the growth, so you can select edges first to fence off an area.
The result becomes one undo step when you close the panel. If you change the selection with another tool while the panel is open, the panel closes.
Expand Selected Edges
Expand Selected Edges adds one layer of edges around the selected edges, for example to widen a contour drawn with the Edge Selector.
- Select edges on the mesh.
- Open the drop-down arrow next to Expand Selection and choose Expand Selected Edges.
The tool works at once, without a panel. It takes the vertices of the selected edges, adds their neighboring vertices and selects every edge between these vertices. A contour one edge wide becomes a band of edges.
The button is unavailable when the mesh has no selected edges. To remove a layer of edges, use Shrink Selected Edges.
