Geometry & modeling
Mesh
Definition
A mesh represents a shape as a surface of small flat polygons, almost always triangles, joined at shared edges and vertices. Meshes work well for rendering, games, and 3D printing, but they have no true faces, edges, or exact curves, so they are hard to dimension or edit as engineering geometry.
Also known as: polygon mesh, triangle mesh, tessellated geometry, polygonal model
Updated
What a mesh stores#
The simplest mesh formats store almost nothing else. The STL format is a list of triangular facets, each defined by a unit normal and three vertices. It has no scale information, so the coordinates are in arbitrary units and the receiving program has to assume millimeters or inches.
Richer formats such as OBJ, glTF, and 3MF add colors, materials, textures, units, or multiple objects. The geometry itself is still a set of flat polygons.
Approximation and resolution#
A curved surface in a mesh is only as accurate as its tessellation. A hole might be a 16-sided or 256-sided tube depending on export settings. Finer meshes look smoother and produce bigger files, but they never become a true cylinder with a single radius.
Mesh quality#
Mesh tools care about whether the surface is closed and consistent. The 3MF Core Specification requires meshes for model objects to have manifold edges, where every triangle edge is shared with exactly one other triangle, and consistent triangle orientation. The OpenSCAD manual warns that an imported STL must be manifold, without holes or self-intersections, or later boolean operations can fail.
Mesh in CAD work#
Meshes are normal for 3D printing, scanning, visualization, and simulation meshes for FEA. They are a poor starting point for mechanical design changes. Most CAD programs can import a mesh and even convert it to a solid, but the result is usually a body made of thousands of triangular faces rather than a few clean surfaces. For AI tools, mesh output is the main sign of text-to-3D rather than text-to-CAD.
Sources
Related terms
B-Rep
B-Rep is the way professional CAD kernels describe a solid: by its boundary, made of exact surfaces (faces), the curves where they meet (edges), and the points where edges end (vertices). Because the geometry is exact and the topology is explicit, B-Rep models can be measured, filleted, dimensioned, and manufactured precisely.
STL
STL is a simple mesh file format that stores a surface as a list of triangles, each with a normal and three vertices. It is the long-standing default for 3D printing, but it has no units, colors, or exact geometry.
Manifold
A manifold mesh is one where every edge is shared by exactly two triangles, so the surface clearly separates inside from outside. Slicers, mesh booleans, and CAD imports rely on manifold geometry to behave predictably.
Text-to-3D
Text-to-3D is AI that generates a 3D shape from a text prompt for visuals, games, or 3D printing, usually as a mesh or neural representation. It targets appearance rather than exact dimensions or editable CAD features.