[Figures 24 & 25] Paraform has powerful surfacing tools that can create great models. Images courtesy of Paraform Corp.

A few of the software packages that apply NURBS surfaces to scanned polygonal data sets are Raindrop Geomagic, Paraform, RapidForm and Cyberware CySlice. Some of these packages have advantages over the others. Paraform seems to have been able to create scan data cleanup tools, curve building tools, and surfacing tools that are very powerful and easy to use. Some of the work produced using Paraform is shown in Figures 24 and 25. Paraform has been used in many films, including Hollow Man, End of Days and Harry Potter and the Sorcerer's Stone.

The process of applying NURBS surfaces onto dense scan data is usually done in the following steps:

1. The scan data is imported into the system. The file format used for importing the data depends on which software is being used for surfacing and which file format was exported from the scanner.

2. The scan data is cleaned up. During the cleaning process, seal all the holes that exist in the scan data and ensure that the surfaces of the scanned data are free from surface discontinuities (noise) and irregularities caused by the scanning process.

3. The boundaries for each surface are laid out. Some software has defined a workflow for the surfacing operation so that only one surface can be made at a time. Some products, however, enable the user to lay out the entire model before creating any surfaces. Creating all the boundaries for all the surfaces can be advantageous. When this type of model is built, the success of the model depends largely on how the surfaces are laid out. A lot of time is wasted if the modeler has to reorganize the surfaces after the model is built. Paraform, one of the packages mentioned earlier, is built so that the patches can be laid out prior to surfacing. Paraform also has one of the most impressive toolkits on the market for laying out the exact parameterization of each surface and determining tangency conditions with accuracy and control.

4. The surfaces themselves are built. Sometimes, as is the case with Paraform, an additional step is required before surfacing, which requires the construction of a spring. A spring is a mesh that stretches between the curves that identify the surface boundaries. This mesh determines the density and accuracy of the surface that will be built on top of the spring. Although this step takes additional time, the benefits are paid back to the modeler by providing additional control. During the process of surfacing these boundary curves, there will be some areas where the curves, for some reason or another, are not exactly right for creating a surface. These conditions are places where the curves cannot meet exactly or have small breaks. At this point, the modeler must replace the curve or edit the curve to get the surface to build. Again, Paraform has excellent curve-editing capabilities.

Wrapping NURBS surfaces onto dense polymeshes holds the promise of creating complex patch models from objects that already exist. The only limitation to thistechnology, it seems, is that it will not create objects that do not already exist. The models that can be imported into these packages do not necessarily have to be scan data. Many polygonal objects can be quickly and easily built and imported into these packages. By building a rough polygonal model and using a smoothing function to increase the resolution of the model, the modeler can quickly create a complex patch model for a low-resolution polygonal model. Using this methodology, modelers can create anything they desire using this software.