Just scratching the surface

Citation

(2002), "Just scratching the surface", Sensor Review, Vol. 22 No. 3. https://doi.org/10.1108/sr.2002.08722caf.006

Just scratching the surface

Just scratching the surfaceKeywords: Distance, 3D scanning

Surfacing software has come a long way in the last 10 to15 years. Whereas now, the creation of accurate surfaces from point clouds is often regarded as integral to the manufacturing process, in the late 1980s, surfacing modules were incorporated almost as an afterthought in the major CAD packages – if they were there at all as most functionality was based on the creation of geometric entities. The potential positive impact of an accurate digital representation on overall design was paid scant attention compared to the time spent on the creation of expensive physical prototypes which often deviated wildly from the original concept model.

During this period manufacturers of 3D CAD software such as Dassault/IBM, Unigraphics/McDonnell Douglas and Parametric Technology Corporation had begun to address the role of surface creation and the need for it to be available to their customers. However, the modules that were first developed bore little resemblance to the sophisticated, dedicated surfacing packages on the market today, and the ability to handle large point clouds was severely limited if present at all.

Instead, these modules were far from easy to use and were unable to handle the creation of surfaces from point clouds, relying instead on sparse cross-sectional data. It is clear that the surfaces produced by these modules were unlikely to offer the degree of accuracy required, given the incomplete nature of the data sets and the lack of tools to create complex styling surfaces.

In the world of automotive design, surfaces as a medium were more widely used, with packages such as ICEM Surf and Alias Wavefront among the most popular.

ICEM, in particular, saw significant service in automotive styling becoming one of the standard packages used in automotive.

The fact remained that in order to progress, surfacing software as a whole needed the capability to deal with complex shapes and more specifically with point clouds, particularly in the light of the expanding use of three-dimensional scanning equipment at this time, not least in the automotive and product design fields.

The gap in the market was initially filled by Imageware, whose Surfacer package was the first designed specifically to create surfaces from mass point clouds and remains, in its latest incarnation (SDRC I-DEAS 9 Imageware products), one of the most powerful tools of this kind on the market today.

More recently, the leading solid modelling providers, such as Dassault Systemes/IBM (makers of CATIA) and Unigraphics, have greatly extended their surface modelling capability in order to provide a hybrid form of solid and surface modelling. Other providers have gone down the acquisition route purchasing and integrating high-end surface modelling technology. Two of the more significant examples of this were the purchase of ICEM Technologies by Parametric Technology Corp and the acquisition of Imageware Inc by SDRC.

Packages such as the above are referred to within the reverse modelling (or engineering) community as "classical" surfacing packages. Such packages provide a very high quality surface, but at a premium in terms of time, operator skill and involvement especially when class A surfaces are required.

The accuracy, in terms of model quality, of current "classical" surfacing packages is unquestioned but the time investment required, the high cost of employing a trained surfacer – who may not always be fully employed – and the fact that at early stages in the design process, this degree of accuracy may not be required, led in the late 1990s to the development of the first rapid surfacing packages.

Rapid surfacing packages, such as Geomagic Studio, Paraform and CopyCad, take a point cloud, create a polygonal mesh and then fit a surface(s) around the mesh. The accuracy of the fitting techniques can then normally be modified locally and globally. While at first they struggled to gain acceptance from the "classical" surfacing fraternity, they have come to the forefront as financial and time pressures on manufacturers continue to grow (Plate 6).

The key advantage of rapid surfacing as a technique is not surprisingly its inherent speed – often a fraction of the time taken to create a surface model using a "classical" approach. On some models, such as an automotive exterior, the overall time difference might not be that great but on extremely organic freeform models the difference could be days or even weeks. This might seem like a rather outrageous claim but consider the degree of difficulty in using a "classical" approach to surface a human face.

Plate 6 A high quality photorealistic virtual prototype of a spray gun created using Geomagic Studio from Raindrop Geomagic

Rapid surfacing also addresses the issue of ease of use for the occasional user. It is recognised that surfaces are used in some industries more than others, with only approximately 20-30 per cent of all CAD users requiring surface capability (Plate 7). Therefore, having permanent surfacing staff in house is often viewed as a luxury. However, as rapid surfacing techniques claim not to require the same degree of operator skill and training as do classical surfacing they hold out the possibility of the occasional user being able to quickly produce surface models. This of course makes surfacing more accessible to companies and industries previously excluded on the basis of cost and insufficient in-house capability.

Plate 7 Virtual prototype of a mainifold, created using "reverse modelling" technology that takes advantage of 3D scanning and rapid surfacing techniques

The faster turnarounds achievable through rapid surfacing do carry a cost. The ability to fit surfaces accurately to freeform point clouds in this way requires the surfaces to be fitted as highly parameterised NURB surfaces, whereas "classical" surfacing typically produces lower degree surfaces, often Bezier. Additionally the initial result from such a process is often dependent on the quality of the physical prototype. If for example there is an area missing then there are often limited tools for conceptual modelling.

Nevertheless, the lure of at least partially "deskilling" the surfacing operation and automating the surfacing process remains attractive, and increased market share is being enjoyed by rapid surfacing packages which continue to develop apace.

Recent developments include an announcement by Unigraphics of their Quickshape module based around Paraform software, and a strategic agreement between PTC and Raindrop Geomagic which will see Raindrop Geomagic Studio technology incorporated into future versions of Pro/ENGINEER, mechanical computer-aided design (MCAD) software, and ICEM Surf.

The introduction of rapid surfacing modules into mainstream 3D CAD packages inevitably means the frontiers for the use of rapid surfacing will be pushed back even further, particularly into areas where the level of accuracy demanded has traditionally been very high and the use of classical surfacing has therefore normally been regarded as de rigueur. Sectors which are seeing greater use of rapid surfacing include large-scale CAD operations such as those which have traditionally been the domain of "classical" surfacing tools such as automotive and product design (Plate 8).

This use of rapid surfacing is likely to grow further and could potentially help to avoid the types of situations which have occurred in the past, where the design model and engineering model have deviated between concept and first-off manufacture. Rapid surfacing at each stage of modification of the model will keep a check on the impact of modifications on the size and shape of the model and ensure it remains within the prescribed dimensional parameters, and so avoiding potentially costly design modifications after the first-off manufacturing stage.

Plate 8

Combining the best aspects of rapid and classical surfacing packages is something which is now being addressed by the industry. Companies producing classical surfacing tools may well look to exploit the growing demand for rapid surfacing by developing modules which allow them to offer a complete surfacing solution in one package, again appealing to the "one-stop shop" mentality of the major manufacturers. The recent merger between EDS with its Quickshape module and SDRC with its Imageware product line looks the most promising candidate for a hybrid classical/rapid surfacing package.

While there is an argument that in some markets there is not sufficient demand for both rapid and classical surfacing, the fact remains that in other areas companies will want a fast representation for initial testing and packaging followed by a more accurate surface at a later stage of the process – and therefore, those packages equipped to offer both rapid and classical surfacing competencies will be at an advantage.

For further information contact: Jim Clark, Business Development Manager, 3D Scanners UK, The TechnoCentre, Coventry University Technology Park, Puma Way, Coventry, CV1 2TT, UK. Tel: +44 (0)24 7623 6575; Fax: +44 (0)24 7623 6576; E-mail: jclark@3dscanners.co.uk