Machine Design

Surface modeler makes multisided patches

The FreeDimension modeler for conceptual and industrial design differs from standard surfacing software by making multisided patches using a patentpending N-Sided Surface technology.

FreeDimension's six and seven-sided patches align perfectly on feature curves and boundaries of a car object.

FreeDimension handles difficult design tasks such as converging six fillets of differing radii with different setbacks. It created an interior blend comprising a single, 12-sided patch.

A simple object has points, handles, and ribbons that affect the object's shape. Pulling the ribbon (upper right) causes that area of the surface to get larger. Twisting the ribbon (lower left) curls the surface near it.

A hairdryer design included a fillet that dissipated at one end. The number of points, handles, and curves was reduced without really changing the geometry, which yielded a better-looking object.


It replaces the more conventional foursided Bezier and Nurbs surfaces found in what's sometimes called "square modeling." The multisided approach helps designers get their creative juices flowing because it closely mimics how users typically work when sketching concepts with pencil and paper.

The software lessens the burden of laying-out patch networks to build up objects. Patches easily fit expected configurations of object features. Users can, for instance, simply make a triangular patch instead of shoehorning rectangular patches to fit a triangular region. Better yet, designers don't have to think in terms of patches at all and instead can focus on the feature curves of objects. That's because N-sided patches align easily with an object's natural features. And there are no collections of subpatches lurking underneath main surfaces.

The software's design flexibility makes trimming patches less important, although the facility is available. Far fewer patches are required for typical designs. An example comes from a difficult design that involved a vertex blend with six fillets of varying radii and setbacks meeting the vertex. To handle the blend, the software generated an interior blend comprising a single, 12-sided patch. This would be exceedingly difficult with a conventional modeler.

Surface input comes from curve creation and tangent "ribbon" (lofted surface) manipulation, with many supporting operations such as global deformations, reflections, snaps, and constraints. Users generate curves by defining points and so-called "handles" or tangent vectors in space. This is similar to the Adobe Illustrator method except it's in 3D. Designers can use any number of points and handles on curves without worrying about ripple effects on other boundaries, a potential problem with Nurbs curves.

Ribbons are defined by "surface handles" or cross tangents to the curve that control the slope of the surface. Aligning surface handles from two adjoining patches provides G1 (tangential) continuity between patches.

FreeDimension is essentially a surface modeler but it can calculate volumes when surfaces enclose them. A B-spline surface converter outputs standard surfaces. Also, the software accepts SketchUp models and outputs to OBJ, STL, and IGES polygon files as well as Nurbs. The program creates compact databases, which hold data such as points, tangent vectors, and pointers from the face. And user interaction is optimal because the computation order is linear in the number of features added (plotting algorithm speed against an increasing number of features would produce a straight line).

In a recent application, a hairdryer design included a rather challenging fillet that dissipated at one end. After putting together the hairdryer body, I simplified the design reducing the number of points, handles, and curves, without really changing the geometry. This yielded a betterlooking object that consisted of only three other patches. The entire body half contained only 10 patches. In that regard, FreeDimension actually rewards users for "thinking simple."

There are a few minor problems with the software. For one, it does not include a true subdivision feature. This lets users drop curves across any face, but the resulting subdivided surfaces no longer matches the original one. This encourages designers to rough in entire objects before fine-tuning. Not a bad habit overall, but some users may find it annoying. The company is working on including the feature. Also, it would be helpful to have a button for creating perfectly circular curves.

FreeDimension is easy to learn because of its few fundamental inputs. The online help with video support is useful. However, the program needs better documentation. The biggest hurdle for novices is adapting to a new way of thinking about design, that of controlling surfaces from curves, handles, and ribbons. But after users clear that hurdle, they can find surprising new design methods.

FreeDimension comes from FreeDesign Inc., 1700 Kylie Dr., Suite 120, Longmont, CO 80501, (303) 956-1158,

— Kun Gao
Kun Gao is a surface-design consultant and can be reached at [email protected].

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.