Parametric solids vs AI meshes: two engines, two jobs

Under the hood, AI 3D generation splits into two very different technologies. Parametric engines write CAD code that constructs exact solids — planes, extrusions, holes, fillets. Mesh engines synthesise a triangulated surface directly, the way an image generator synthesises pixels. Neither is “better”; they are good at opposite things.

When you want a parametric solid

Anything with dimensions that matter: brackets, housings, adapters, gears, fixtures. A parametric solid honours your numbers exactly — a 6.2 mm hole is 6.2 mm — and exports clean STEP for CAD and CAM. It can also be regenerated with changed parameters, which is what makes refine-by-description work.

When you want a mesh

Organic, sculptural, decorative shapes: figurines, stylised housings, ornamental panels, anything you would describe by look rather than by dimension. Constructive solid geometry is genuinely bad at free-form surfaces — asking a parametric engine for a “flowing organic helmet” gets you a lumpy approximation. Mesh generation shines exactly there, and the result prints fine.

The one-way street

Solids convert to meshes trivially — that is just STL export. The reverse is the hard part: a mesh carries no features, so there is no general way to recover a parametric model from it. Converting a mesh to a B-Rep shell is possible for some shapes, but the result is still not an editable feature tree. Decide which side of the street a part lives on before you generate it.

Photos as a starting point

Photo-to-3D runs through the mesh engine: it reconstructs the visible surface. That means dimensions in the photo are estimates, and internal geometry (wall thickness, hidden features) is not captured — if you need a specific wall thickness, state it in text as a spec. For mechanical parts, a photo plus a written spec (“like this bracket, but 80 mm wide with M6 holes”) routes the important numbers through the parametric engine.

Let the router decide, override when you disagree

AiCadGen classifies each request and routes it to the right engine automatically — mechanical language to the parametric engine, sculptural language to the mesh engine. If a request is ambiguous, say which output you want (“as an exact solid” / “as a sculpted mesh”), or set the engine explicitly in the options.