Too many proprietary CAD systems make interoperability impossible. But the situation is about to change. It wasn’t long ago the only way to get a CAD model from one system to another was to first translate it into the IGES format and then translate it into the system at hand. But just as translating spoken languages sometimes mangles the original messages, this so-called neutral-file format could deliver geometry that only resembled the original model. Passing geometry through IGES is likely to separate surfaces at edges, erase essential text, and give blends the heave ho. In the parlance of CAD gurus, the neutral file format does not encourage interoperability.
The IGES format was supposed to provide a conduit for moving geometry built in one system to almost any other. In a perfect world, for example, a designer should be able to create geometry, send it to an analyst for strength studies, and eventually to manufacturing for production without needing cleanup or modification.
But talk to people on the shop floor, and you’ll find that cleaning or fixing models is not the exception – it’s the rule. Mold shops in particular get models from almost every available CAD system. They come in IGES, the widely used DXF format, the international STEP format, and the ACIS®SAT format. And when manufacturing people don’t have a nearly identical CAD system on the receiving side, they have to tweak and adjust models until they have geometry for good tool paths. “Logica launches MMS interoperability solution Logica, the supplier of mobile messaging and mobile payments, has announced that has become the first company to deploy a proven MMS intercarrier messaging solution with a unnamed mobile operator.” (Logica launches MMS 2002)
Flawed files are so pervasive that a few automakers solve the problem heavy handedly by insisting that suppliers use only their approved brand of software. Smaller companies dealing with several automakers must then maintain at least one of every approved CAD system. The method might solve interoperability or translation problems for the big boys, but for third and fourth tier suppliers, maintaining several CAD systems produce a heavy support burden that consumes many thousands of dollars.
There is a light at the end of the tunnel because one company is delivering solutions to this interoperability problem – Spatial Technology Inc. Spatial’s ACIS 3D modeling kernel, the de facto modeling standard, delivers solid, surface, and wire-frame modeling to developers of CAD software, NC packages, analysis programs, and dozens of other products. Departments using ACIS-enabled applications can import SAT models from any of the over 180 ACIS-enabled applications, such as Autodesk’s Mechanical Desktop, Applicon’s Bravo, Baystate’s CADKEY, Ashlar’s Vellum Solids, VDS’s IronCAD, or Knowledge Revolution’s Working Model 3D, and read them flawlessly.
The SAT interoperability works. The good news is about to get better. Spatial’s ultimate goal is to let anyone using an ACIS-enabled CAD system bring in a design, regardless of where it was created, and automatically turn it into usable geometry – watertight models, good enough for finite-element analysis, manufacturing, or other engineering functions.
With the upcoming ACIS 5.0 release, the “interoperability release, ” this goal is becoming a reality. A peek at ACIS 5.0 provides a look at impressive and growing capabilities available from no other single source. For the first time ever, engineers can use any model, regardless of where it’s generated. “A more viable approach is to achieve large-scale interoperability via a network-based solution, using similar principles as communications networks used by Internet providers and voice carriers. Such a network would connect existing systems into regional, statewide or national systems to create a private Intranet for multi-agency interoperability without requiring the purchase of new end-user equipment. ” (Herther 2002)
Users of ACIS-enabled applications can successfully read SAT files from other ACIS-enabled systems and immediately use them. But model flaws can creep into SAT files coming from either legacy or proprietary non-ACIS based applications. Flaws show up in many forms, such as gaps in geometry or surfaces that don’t meet at edges. In Spatial’ s vocabulary, the model fidelity is low and suffers from a lack of precision. Even for this geometry, Spatial now has a few tricks up its sleeves.
The soon-to-be-released ACIS 5.0 is Spatial’s “interoperability release.” For the first time ever, technology will be in place to let engineers turn a wider range of flawed geometry into `watertight’ models for almost any downstream operation. ACIS 5.0 will include enhancements to the company’s groundbreaking ACIS Healing Husk, which turns low- fidelity models into high-fidelity SAT models. And for those models that just can’t be fixed, ACIS 5.0 has capabilities for working with low tolerance models. The result? Interoperability between all applications – either ACIS-enabled or proprietary non-ACIS based. A review of the unique blend of technologies will provide a glimpse at how Spatial’s new interoperability solution works. Key features include:
* The high fidelity (precision) of ACIS
* Data translation
* Tolerant modeling
Interoperability between ACIS-enabled and non-ACIS systems is made possible by the ACIS kernel’s high-fidelity modeling. So what does this high-fidelity mean? If all geometry could be described by classic, closed equations, such as lines, arcs, conics, spheres, cubes, etc., then solid models could provide an exact representation of real-world parts. But some geomesuch as lines, arcs, conics, spheres, cubes, etc., then solid models could provide an exact representation of real-world parts. But some geometry, such as free-form surfaces, can’t be defined by these classic, closed equations. For these elements, kernel modelers use mathematical representations, such as B-splines. And different kernel modelers may have different algorithms for capturing these elements.
The degree to which these different algorithms accurately represent real-world parts is a measure of “fidelity.” In addition, the precision of the representation, mathematical operations, and storage of models contributes to the total “fidelity” of a solid model.
* ACIS is the standard for high-fidelity modeling in terms of both precision and topology richness for representing real-world parts:
* ACIS performs mathematical operations and stores models to a precision of 10-6, which is a precision greater than any other 3D solid modeling kernels.
ACIS also has the richest set of topology (wire frame, surface, solid, hybrid, non-manifold) and the broadest geometry coverage (analytic, NURBS, procedural) for representing the original intent of a design.
Once geometry is raised to the accuracy of the high fidelity ACIS SAT file, it can go anywhere. The precision of ACIS has impressed many others. Data translation begins the process of changing low-fidelity non-ACIS models into high-fidelity ACIS SAT models. ACIS-enabled applications use Spatial’s Translators Husks or other third-party data translators to turn models stored in different file formats, such as VDA-FS or IGES, into ACIS SAT files. (An ACIS Husk is an optional library of task-specific functions that software developers can plug into their ACIS-enabled applications).
The German Automobile Manufacturers Association wrote VDA-FS, a European standard for the transfer of surface data between dissimilar CAD/CAM systems. The neutral file format allows exchanging geometry, topology, and annotation data. Spatial partnered with GSSL of India to produce the ACIS VDA-FS Translator Husk to work with the German standard. Spatial also worked with GSSL to produce the ACIS IGES Translator Husk to work with IGES files. In 1999, Spatial plans to introduce a STEP Translator Husk.
Both the VDA-FS and IGES Husks perform limited cleanup and repair of models, and compensate for some subtle differences between VDA- FS or IGES implementations by various CAD applications. The Husks also provide user-controlled options to tune the accuracy of imported and exported files.
Once a model is translated into a SAT file, and if the file is in need of repair, an ACIS-enabled application can fix the model using the ACIS Healing Husk, the first widely available technology for correcting model flaws. Spatial first released the Healing Husk in March 1998. This month, with ACIS 5.0, Spatial introduces enhanced capabilities for its ACIS Healing Husk. Here’s a glimpse at how the Husk works. The Husk’s analysis software first checks that trimming curves are in tolerance of the surface, and that two faces sharing an edge are within the edge’s tolerance. Other checks by the Husk include looking for faces that should be adjacent to one another.
“The SunPCi co-processor card is the latest addition to Sun’s family of PC interoperability solutions which enables Sun workstation customers to work in the same e-mail, spreadsheet and other office productivity applications as their colleagues in different departments.” (NEW SUN CARD 1998)
Next, the Husk checks to see whether the surfaces can be simplified. ACIS can recognize the NURBS as spheres, cylinders, and cones and translates them into primitives to simplify the geometry. Then the Healing Husk provides information back to users about where problems are in the body. Users can decide whether to fix the models automatically or manually in a process called stitching. Stitching is a bit of a misnomer because it doesn’t’ t exactly bring edges together. Instead it adds topology to a surface model that would allow turning surfaces into a solid.
After stitching, the Husk repairs inaccuracies in the model. It performs a series of geometric operations to improve the precision of face, edge, and vertex data. Finally, the Husk corrects face normal, removes duplicate vertices and faces no longer associated with geometry, and delivers a high fidelity, “healed” ACIS SAT model.
The ACIS Healing Husk provides functions to either automatically heal the entire body or manually heal individual parts of the body. In the manual mode, users can attach attributes to poorly formed model faces that might cause trouble for downstream users. These attributes or notes can be stored for later examination. When the flawed area does not affect users, they may wish to remove the attributes and ignore the problematic geometry.
The ACIS 5.0 release introduces new tolerant modeling capabilities in the kernel. Tolerant modeling will let ACIS 5.0-enabled applications work with low-tolerance models when geometry just can’t be fixed through healing. The philosophy chosen by Spatial is to work with tolerances on edges and vertices rather than trying to turn poor geometry into perfection. The approach is to tolerate imperfections and work around them ¬ let the software heal as much as possible and then attach tolerance information to uncorrectable areas. Tolerant modeling is the technology that will make ACIS 5.0-enabled applications essential to every engineering department.
New tolerant edge and vertex capabilities will let the software attach tolerance values to them. So even when edges do not exactly intersect, they’re brought close enough to be useful. Some CAD systems put out models so flawed users might import only a set of surfaces that should be a solid. Two edges might be stitched to one tolerance and another two edges to a different tolerance. Tolerant edge technology will let users work with these flaws. The last component of Spatial’s new interoperability solution is its viewing technology. Spatial has recognized that not everyone needs to modify geometry. Just examining it might be enough.
The ACIS 3D Open Viewer makes ACIS SAT models conveniently and widely available to an entire organization by letting its staff view models in Microsoft Office applications, like Word, PowerPoint, and Internet Explorer. Professionals in sales, marketing, finance, publications, engineering, and support can create information-rich 3D multimedia presentations, documents, and proposals using models developed in any of the over 180 ACIS-enabled applications. Users can rotate, pan, or zoom these models, and control their background and colors.
“Businesses also should address interoperability issues such as encryption (in individual stores and across transport), access control, replication, conflict resolution, content preservation, mapping (threads and links), data consistency and large text searches across environments. In addition, they may have to provide many simultaneous users with optimum performance and handle multiple data types such as image, voice, video and binary files.” (Cox 1997)
The ACIS kernel is established as a de facto modeling standard. ACIS 5.0 will cement the standard. Improved model interoperability combined with tolerant modeling and healing technology are the best reasons yet to take advantage of applications based on ACIS 5.0. And there are others. For example, Spatial’s top- notch development team has delivered more impressive features with ACIS 5.0 – all at an industry-leading pace – including new selective Booleans, enhanced blending capabilities, new bending functionality, and additional error-feedback features. New selective Booleans allow combining two or more bodies with greater flexibility and speed by letting users keep or discard a portion of these combined bodies. Users can pick, color, and highlight portions of the model they wish to keep or discard.
In ACIS 5.0 bending has been repackaged for far easier use. A user can now bend a part of a body by specifying where to bend it and between which limits, saving incredible amounts of time. For example, users can take a straight metal cylinder and bend it quickly and easily into a bicycle handlebar. Moreover, the speed of bending has been greatly improved and intelligence has been added to automatically determine which connected parts of a body also have to be bent.
The new spray system boosts the helicopter’s productivity by increasing the pesticide-tank capacity so the aircraft stays airborne longer. Previous systems used rectangular metal tanks attached to the underside of the aircraft. The tank volume was limited by the need to clear the landing gear and communications equipment on the helicopter. Vellum Solids made the design task more manageable because it’s based on the ACIS 3D modeling kernel which allows designing with wire frame, surfaces, and solids in one model. Most midrange solid-modeling programs make it necessary to model the tank only in solids because they do not offer surface modeling. Several are just beginning to include rudimentary surfacing functions. Such programs would require creating many different solid primitives representing various pieces of the tank. The designer would have had to position them correctly in relation to each other and then use Boolean commands to join them or subtract them out.
The open-hardware architecture of the PC bus often gets credit for fueling the personal computer revolution. In a similar way, the open- software architecture of the ACIS 3D modeling kemel works as a geometry bus, driving “plug-and-play” compatibility and freedom of choice in solid-modeling systems. The kernel is a foundation on which over 180 companies have written applications for special engineering functions. Models move seamlessly among these applications via the ACIS Geometry Bus by using the industry standard ACIS SAT file format. This means a wide range of engineers can use a single model throughout the product development process, from concept to manufacturing, using applications from multiple vendors without the hazard and burden of translating data. There is no need to suffer the drudgery and time wasted in fixing broken models. Such essential repair is the most time consuming problem for shops and facilities using high-cost closed proprietary design and manufacturing systems. The ACIS 3D modeling kemel provides a clear route around that roadblock.
Cox, Nancy, “Bridging The Interoperability Gap”, Network Computing, 03-01-1997, pp p. 112
Herther, Jay, “The interoperability quandary”, Mobile Radio Technology, 08-01-2002
“Logica launches MMS interoperability solution”, Europemedia, 11-21-2002
“New Sun Card Provides Workstation With Pc Compatibility” Vol. 11, Computer Workstations, 10-01-1998, pp. 4-5