CAD and NURBS modeling for games

CAD and NURBS modeling describes shapes with exact mathematical curves and surfaces instead of a mesh of flat polygons. NURBS stands for Non-Uniform Rational B-Splines (GameFromScratch: Plasticity NURBS Based 3D Modeller). NURBS models "are vector-based and mathematically defined", so they stay smooth at any size (GarageFarm blog: The new face of NURBS Modeling: Plasticity 1.3). Games still need polygons, so every CAD model must eventually be converted (tessellated) into a mesh.

#NURBS vs. polygons

A polygon mesh is "connected faces/polygons (3, 4, N-sided)", while a NURBS model is "built from points, curves and surfaces" and stays resolution-independent, editable and measurable (moi3d.com: Moi3d Overview). In practice that means:

For hard-surface modeling, the main advantage is fillets. In Plasticity, Fillet Shell takes a positive distance to fillet an edge and a negative one to chamfer it, and supports variable distance, conic and G2 (curvature-continuous) fillets (Plasticity documentation: Fillet Shell). On a polygon model, the equivalent requires bevels, support loops or tools like MESHmachine (machin3.io: MESHmachine documentation).

#The tools

• Plasticity. A NURBS modeler by Nick Kallen's Plastic Software that CG Channel calls "CAD for artists", positioned as "a low-cost, artist-friendly alternative to tools like MoI and Fusion" (CG Channel news article on Plasticity 2026.1). It started as a tool "for concept artists" (GameFromScratch: Plasticity NURBS Based 3D Modeller). It is sold as perpetual Indie and Studio licences; Indie exports OBJ, STEP, STL and Parasolid, and Studio adds more formats (CG Channel news article on Plasticity 2026.1; Plasticity documentation: Import/Export). A Blender bridge add-on transfers mesh data between the two apps (GarageFarm blog: The new face of NURBS Modeling: Plasticity 1.3). Its Boolean command combines, subtracts or intersects solids and sheets (Plasticity documentation: Boolean).
• MoI (Moment of Inspiration). A NURBS modeler by Michael Gibson; its native 3DM format is "OpenNURBS / Rhino 3D compatible" (moi3d.com: Moi3d Overview). Its mesh export can output N-gons, quads and triangles, or triangles only (moi3d.com: Moment of Inspiration 4.0 command reference…).
• Rhino. The established NURBS modeler that MoI's 3DM format is compatible with (moi3d.com: Moi3d Overview). Plasticity's Studio licence imports Rhino files, BREP/NURBS/curve data only (Plasticity documentation: Import/Export).
• Fusion. Autodesk's CAD tool. Its OBJ export uses mesh refinement settings for surface deviation, normal deviation, maximum edge length and aspect ratio (Fusion API documentation: OBJExportOptions Object).

See modeling software for the wider landscape.

#Converting to meshes for games

#Tessellation

On export, the tool approximates each surface with polygons within a tolerance. Tighter tolerances follow curves more closely and cost more polygons.

Each tool names the controls differently:

• Plasticity offers Tris, Quads or Ngons topology, a single Density slider that adjusts the other values, and tolerances for face and edge deviation (in cm) and angle (in radians). Face Plane Tolerance is "One of the most effective ways to control polygon count"; the docs suggest 0.01 for low poly and 0.0001 for high poly, and edge and face angle tolerances of 0.35 (low) and 0.15 (high) (Plasticity documentation: Export OBJ). Remove Small Features drops details below a size threshold, which the docs describe as ideal for high-to-low work (Plasticity documentation: Export OBJ).
• MoI uses an Angle setting: "The Angle option controls the maximum angle allowed between the surface normals at the corners of each polygon." It warns that "Some programs have difficulty dealing with complex N-gon shapes" (moi3d.com: Moment of Inspiration 4.0 command reference…).
• Fusion exposes surface deviation (cm), normal deviation (radians), maximum edge length and aspect ratio (Fusion API documentation: OBJExportOptions Object).

#Three ways to use the export

1. As a high poly for baking. Export dense, triangulated, and bake onto a separate low poly (see the high-to-low workflow). Topology does not matter here, which suits CAD output.
2. As the start of a game mesh. Export at low density with N-gons, then clean up and retopologise in a polygon tool. Expect to fix long thin triangles around fillets.
3. As reference. Use the CAD model as an exact guide to rebuild a game mesh by hand. At Angelic, the concept department supplies Fusion 360 meshes as reference for the hard-surface artists (80 Level: Creating Assets Within the Mid-Poly Workflow…).

#Who uses it

Plasticity's early pitch was "a 3d modelling software for concept artists" (GameFromScratch: Plasticity NURBS Based 3D Modeller). Newer marketing targets hard-surface modelers, prop designers and Blender users looking for a gentler learning curve (GarageFarm blog: The new face of NURBS Modeling: Plasticity 1.3). MoI's own overview lists CAD, CAM, CNC and 3D printing uses, and courseware for a jewellery design department (moi3d.com: Moi3d Overview).

#Further reading