Some NURBS properties do not convert

If you create subdivision surfaces from the following types of NURBS surfaces, you may get unexpected results.

• Degrees other than 3 (cubic) are not converted.
• Rational geometry (weighted CVs) is not converted.
• Trimmed regions on a NURBS surface are not converted
• NURBS spheres converted to subdivision surfaces will have incorrect surface normals at the poles. When viewed in shaded mode the converted sphere will have dark points indicating that the normals are being computed incorrectly.

Consider converting to a polygon mesh first

A subdivision base mesh created from NURBS will probably be too dense, and NURBS models are typically made of different surfaces that must be converted individually and then attached.

By using Modify > Convert > NURBS to Polygons first, you can reduce and attach the polygon mesh before converting to a subdivision surface.

Use the following options with Modify > Convert > NURBS to Polygons > to convert NURBS surfaces to a polygon mesh suitable for use as a subdivision base mesh:

• Set Type to Quads.
• See Tesselation Method to General.
• Set U Type and V Type to Per Surf # of Isoparms in 3D.
• In the Number U and Number V boxes, try to find the lowest numbers that roughly approximate the shape of the surface.

If you converted multiple NURBS surfaces, use Mesh > Combine to merge them into a single polygon mesh. Then use Edit Mesh > Mergeor Edit Mesh > Merge Edge Tool to merge internal border edges. To show border edges clearly, choose Display > Polygons > Custom Polygon Display > and turn on Border Edges.