Loads from YouTube (Google) when you press Play
Orient Mesh Normals finds the parts of a mesh that face the wrong way (inside out) and flips them, so that all normals point outward. Use it when an imported model shows inside-out patches, when its volume comes out negative, or before Boolean operations, offsets and 3D printing, which need a consistently oriented surface.
What flipped normals look like
Every triangle has a front side and a back side, and its normal points out of the front side. On a correctly oriented closed model all normals point outward, so you see only the front sides. MeshInspector draws the back side of a surface in a different color from the front side, so an inside-out part stands out at once. A second sign is a negative Volume in the Information panel.
To see the directions of the normals as short lines, use Inspect › Show Normals.
Fix flipped normals
- Select one or more meshes in the Scene tree.
- Click Mesh Repair › Orient Mesh Normals.
- Keep the default settings and click Apply.
In this example, the main part of a plate model is inside out: the viewport shows its olive green back side, and Volume is negative.
MeshInspector checks every triangle, flips the whole components that face the wrong way, and closes the panel. After Apply, the plate shows its blue front side, and Volume is positive again. To go back, use Undo (Ctrl+Z, or Cmd+Z on macOS).
How the check works
MeshInspector casts a ray from each triangle and counts how many times the ray crosses the surface. Take a closed box: a ray that goes out of a correctly oriented wall leaves the box and never comes back, which is 0 crossings, an even number. A ray from a wall that is inside out points into the box and crosses the opposite wall once, an odd number, so this wall is flipped.
The check counts triangles, but the tool flips whole connected components: a component is flipped when enough of its area faces the wrong way (see Component Threshold below).
Settings
| Setting | What it does | Default and tip |
|---|---|---|
| Mode | How a triangle is checked; the three modes are below. | Shallowest works for most models. |
| Virtual Fill Holes | If the mesh has holes, fills them virtually for the check, so that rays leaving through a hole are counted correctly. The holes of your mesh stay open. | Off. Turn it on for open meshes, such as scans with holes. |
| Component Threshold | A component is flipped when at least this % of its area is oriented incorrectly. | 50% |
The modes of Mode, as the app describes them:
- Positive checks that the ray along the normal crosses the surface an even number of times.
- Shallowest checks one direction, along the normal or against it, whichever has fewer crossings: along the normal the number must be even, against it odd.
- Both Sides checks both directions: along the normal the number must be even, against it odd.
Tips
- Select several meshes to orient them in one run.
- The count of crossings is reliable only on a closed, clean surface. If the result looks wrong, repair the mesh first with the Mesh Healer: its Flipped Normals check uses the same three settings.
- To see which triangles the check finds without changing the mesh, use Select › Select Disorientations.
- To flip a whole mesh, or one component that you pick, by hand, use Flip Normals.
