Best seat in the house

ýPixar uses polygonal and subdivision surfaces modelling technology to create 3D animated characters,¯ Sederberg explains. ýA lot of industrial designers have started to look towards this type of modelling because itÝs much easier to get a nice complex surface with smooth transitions between features.¯

Rhino produces NURBS that start out as rectangular planes, which then can be bent and tweaked to form the curve the designer wants. To make an irregular form that is a self-contained volume, designers typically have to panelise the form with a patchwork of NURBS. With T-Splines, on the other hand, designers can use polygonal or sub-divisional modelling techniques, beginning with a 3D volume that can be stretched, extruded, and twisted, while maintaining the volumeÝs continuity.

The final NURBS computer model is sent to automated CNC mills via IGES files to cut the prototypes and ultimately the moulds for 900 PC aluminium casting.

ýWith T-Splines, we can make a non-rectangular shape that is one surface and smooth everywhere,¯ says Sederberg. ýIf we made this shape in Rhino without T-Splines, we would have to spend a lot of time making sure the edges of composite surfaces patch together correctly without gaps or misalignment. ÙYou donÝt have to deal with patches.Ý -- thatÝs just a few words, but thatÝs essentially what T-Splines mean to Rhino users. ItÝs a huge time-saver.¯

There are a host of polygonal based modellers already on the market, according to Sederberg, including brands like 3ds Max, Hexagon, modo, and Silo. The limitation to these applications has been that they produced pretty pictures ± animation, film effects, or video-game scenes ± but could not be linked to NURBS, which product designers use to communicate geometry to factory machines. Through T-Splines in Rhino, these two separate modelling methods are finally linked in tandem. Polygon-produced shapes can now be produced as real-world objects.

ýT-Splines is the first program to actually do that polygonal modelling in a way thatÝs compatible with NURBS,¯ he says. ýWith T-Splines, you can easily get very complex geometries, and in the end be able to manufacture it.¯

Stanchion production

DondersÝ chairs give an excellent example of how polygons and NURBS can now come together in a design process.

ýMany of the chair parts are surfaces that Rhino can model very well all by itself,¯ says Sederberg. But one highly detailed part - the ornately curled stanchion under the arm of the chair - makes it a prime candidate for polygonal manipulation.

ýI donÝt think you would even dream of modelling something like that in Rhino. ItÝs something thatÝs easy to model in the T-Splines plug-in, but for someone whoÝs already familiar with polygonal modelling, itÝs also easy for them to model the entire shape in a polygonal modelling application.¯

Donders modelled the stanchion in a popular polygonal modelling program called Hexagon, and then brought it into T-Splines in Rhino, where he seamlessly converted the shape to NURBS. ýItÝs just a push-button operation to convert the data. Without additional work or editing, the designer has an extremely complicated ironwork design ready for fabrication,¯ says Sederberg. ýThe Blackpool project focuses on one aspect of the T-Splines plug-in ± the ability to convert low-polygon-count meshes to T-Splines inside Rhino, so that the form can be manufactured,¯ Sedenburg says.

As for the Grand Theatre, the audiences are now seated in style after the completed restoration. Donders may have stumbled upon something big with his revival design. ýThe architect who built the Grand in 1894, Frank Matcham, built almost 30 other public auditoriums and music halls throughout the UK,¯ says Donders. The popular appeal of MatchamÝs theatres has spawned a national society to preserve his work. Donders has just received orders for hundreds more chairs - to fill rows in the Royal Hall in Harrogate, as well as another location in the West End of London.

The T-Splines plug-in for Rhino version 1.0 was released in September 2007, and is now available through the companyÝs website, or through various Rhinoceros resellers. The module contains a suite of polygonal modelling and surface building tools, along with the flexible data translation capabilities for models from other applications.

www.peterdonders.com
www.tsplines.com
www.rhino3D.com