Geometry model

A geometry model is the specific digital representation a piece of software uses to store and reason about a part's shape, such as a boundary representation (B-rep), a triangular mesh, or a point cloud. Different geometry models trade off precision, file size and how easily they support operations like feature recognition or simulation.

Why geometry model choice matters for manufacturing software

Converting between geometry models, such as from a B-rep to a mesh for visualization or simulation, typically loses exact parametric information (like the true radius of a fillet), which is why manufacturing software generally prefers to work from the original B-rep where possible.

Where this comes up

Not shown on a drawing; it is a property of the digital file a part is delivered in (STEP, native CAD, mesh formats like STL) rather than the drawing itself.

Common mistakes

Assuming any 3D file format is interchangeable for manufacturing purposes. An STL mesh, common for 3D printing, discards the exact parametric geometry a CNC feature-recognition or CAM system typically needs.

Is a geometry model the same as a CAD file format?

Related but not identical; the file format (STEP, native CAD, STL) determines how a geometry model is stored and exchanged.

Why can't manufacturing software just use an STL file?

Because STL represents a shape as a triangular mesh approximation, discarding the exact curves and surfaces (like a true circular hole) that manufacturing calculations rely on.

Is a B-rep the best geometry model for manufacturing?

For most CNC manufacturing purposes yes, since it preserves exact geometry; other representations suit other purposes, like meshes for visualization or simulation.