Producing Geometry You Can Trust
QC provided an engineer for our project who did a great job of collecting the dimensional data for the parts to be reverse engineered, creating the CAD models, and producing prints for manufacturing. He kept in regular contact with me throughout the project, allowing us to quickly resolve issues as they arose. He was also very responsive when asked to make changes to the prints. Overall, a superior job.
- Paul,
Power Generation
NURBS Surface Models
A NURBS surface model is constructed of numerous non-parametric surface planes – a method best suited for organic shapes. Individual features are not editable in a NURBS model, which is often referred to as a "dumb solid". The model can be cut, scaled and features added to it. But it cannot be offset from.
NURBS surfacing is often used when every aspect of the part must be replicated (including defects) as accurately as possible – such as for Finite Element Analysis (FEA). All surface variations are replicated - including texture if necessary. Accuracy of results are very dependent on the steps taken in the post-processing of the scan. This is the most accurate method of reverse engineering exact geometry.
Development of NURBS (Non Uniform Rational Basis Spline) began in the 1950s by engineers who were in need of a mathematically precise representation of freeform surfaces like those used for ship hulls, aerospace exterior surfaces, and car bodies, which could be exactly reproduced whenever technically needed. Prior representations of this kind of surface only existed as a single physical model created by a designer.
The pioneers of this development were Pierre Bézier who worked as an engineer at Renault, and Paul de Casteljau who worked at Citroën, both in France. Bézier worked nearly parallel to de Casteljau, neither knowing about the work of the other. But because Bézier published the results of his work, the average computer graphics user today recognizes splines — which are represented with control points lying off the curve itself — as Bézier splines, while de Casteljau’s name is only known and used for the algorithms he developed to evaluate parametric surfaces. In the 1960s it became clear that non-uniform, rational B-splines are a generalization of Bézier splines, which can be regarded as uniform, non-rational B-splines.
At first NURBS were only used in the proprietary CAD packages of car companies. Later they became part of standard computer graphics packages. Today NURBS can be a cost-effective output from virtually all scanning software systems.
