Mesh Basics & Terminology
Meshmixer operates on triangle meshes, which are objects comprised of three types of elements: vertices, edges, and triangles.
- Vertices are points in 3D space. We can also associate other information with vertices -- for example, color.
- Edges are connections between pairs of vertices.
- Triangles are triples of vertices.
In Meshmixer we also use the term faces to refer to triangles (though really triangles are only one type of face). Edges connect the corners of triangles, and vertices are points where two or more edges meet (corners of the triangles).
We use the term neighbours to refer to two triangles that share an edge, two edges that share a vertex, or two vertices that share an edge. We use the term incident to refer to an element that is part of another. For example, an edge is “incident upon” one or more triangles.
A mesh boundary is one or more edges incident upon only one triangle. A mesh is called open if it has one or more boundaries, and closed if it has no boundary edges.
A shell is a connected set of triangles. In other words, starting from one triangle, you can walk to any other triangle in the shell without leaving the surface. This is also sometimes referred to as a connected component.
Surface normal and tangent: you can think of a tangent plane at a point on the surface as the plane that is parallel to the surface at that point. The normal vector at a point is the vector that is perpendicular to this tangent plane. You can think of the normal vector as the vector that points “straight out” of the surface, and the tangent as the plane that fits “along” the surface at a given point.
UVs/Texture coordinates: UV mapping associates with each vertex in the mesh a 2D coordinate. This allows for texture mapping, which "wraps" a 2D image onto a 3D surface. The texture coordinates or UVs are the set of 2D coordinates for all triangle vertices.
Manifold vs non-manifold: A manifold surface has either one or two triangles neighbouring every edge in the mesh. A non-manifold surface can have three or more triangles on a single edge. Usually there are only a small number of non-manifold edges in a non-manifold mesh. See the section on Complexes for more details.
Meshmixer allows you to assign a tag to any triangle in the mesh. These tags are represented by colours in the application. A set of triangles with the same colour (or tag) is called a Face Group.
NOTE: To see face groups, you must choose Group Color (Default) in Mesh Color Mode in the preferences window.
To assign a set of triangles to a new Face Group, select them using the Select tool, then choose Modify > Create FaceGroup. To remove the Face Group identifier from a set of triangles, select the triangles and click Modify > Clear FaceGroup.
Once you have one or more Face Groups you can do things with them. In Select mode, double click inside a group to select the entire group. Some tools are also aware of Face Groups. For example, in the Remesh tool, you can check the option Preserve Group Borders:
This will make it so that the shape of the Face Group is preserved, even if we add or remove triangles. In this example, notice that the outline of the green face group remains the same, even as many triangles are added inside and outside of the group.
The Stamp tool creates shapes in the mesh by refining the mesh (inserting vertices, edges, and triangles), and assigning triangles to Face Groups.