Solid Modeling Solutions: Difference between revisions

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==History==

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The development of ''Non-Uniform Rational B-Spline'' (NURBS) originated with seminal work at [[Boeing]] and [[SDRC]] (Structural Dynamics Research Corporation) in the 1980s and '90s, a company that led in mechanical computer-aided engineering in those years.<ref>[http://isicad.net/articles.php?article_num=14940 "NURBS and CAD: 30 Years Together"], Ushakov, Dmitry, isicad, December 30, 2011.</ref> Boeing's involvement in NURBS dates back to 1979, when they began developing their own comprehensive CAD/CAM system, TIGER, to support the diverse needs of their aircraft and aerospace engineering groups. Three basic decisions were critical to establishing an environment conducive to developing NURBS. The first was Boeing's need to develop its own in-house geometry capability. Specifically, Boeing had complex surface geometry needs, especially for wing design, that could not be found in any commercially available [[CAD/CAM]] system. As a result, the TIGER Geometry Development Group was established in 1979 and has received strong support for many years. The second decision critical to NURBS development was the removing the constraint of upward geometrical compatibility with the two systems used at Boeing at that time. One of these systems had evolved due to the iterative process inherent to wing design, while the other was best suited for adding to the constraints imposed by manufacturing, such as cylindrical and planar regions. The third crucial decision was simple but essential: adding the "R" to "NURBS." Circles were to be represented precisely, with no cubic approximations allowed.

By late 1979, there were five or six well-educated mathematicians (PhDs from Stanford, Harvard, Washington, and Minnesota). Some had many years of software experience, but none of them had any industrial, much less CAD, geometry experience. Those were the days of the oversupply of math PhDs. The task was to choose the representations for the 11 required curve forms, which included everything from lines and circles to Bézier and B-spline curves.

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There are two reasons why NURBS wereIGES so quickly accepted by IGESNURBS. The first was that IGES was in great need of a way to represent objects. Up to that point, there were, for example, only two surface definitions in IGES, and the B-spline form was restricted to cubic splines. The other, surprisingly important, reason for the rapid acceptance was that Boeing, not being a CAD system supplier, was not a threat to any of the major turnkey system vendors. Evidently, IGES easily bogs down when different vendors support their own slightly different representations for the same objects. At this first IGES meeting, it was discovered that the peopleSDRC withrepresentatives the best understanding ofunderstood the presentation were the SDRC representativesbest. Evidently, SDRC was also active in defining a single representation for standard CAD curves and was working on a similar definition.

Boehm's B-spline refinement paper from CAD '80 was of primary importance. It enabled the staff to understand non-uniform splines and to appreciate the geometrical nature of the definition so as to use B-splines in solving engineering problems. The first use of the geometrical nature of B-splines was in the curve/curve intersection. The Bezier subdivision process was utilized, and a second use was our curve offset algorithm, which was based on a polygon offset process that was eventually communicated to and used by SDRC and explained by Tiller and Hanson in their offset paper of 1984. The staff also developed an internal NURBS class taught to about 75 Boeing engineers. The class covered Bezier curves, Bezier to B-spline and surfaces. The first public presentation of our NURBS work was at a Seattle CASA/SME seminar in March 1982. The staff had progressed quite far by then. They could take a rather simple NURBS surface definition of an aircraft and slice it with a plane surface to generate an interesting outline of some of the wing, body and engines. The staff were allowed great freedom in pursuing our ideas and Boeing correctly promoted NURBS, but the task of developing that technology into a useable form was too much for Boeing, which abandoned the TIGER task late in '84.