Off the shelf plug-and-play CAD/CAM

Dave Wilson looks at a new way to obtain interoperability in the world of Windows-based CAD/CAM

The CAD/CAM world is currently divided between those packages that support Windows and Windows NT and those that prefer the world of UNIX. In both camps, software developers have recognised that to compete in the mechanical engineering marketplace in the long term, they must provide software that can interoperate with other packages.

Future CAD packages will become even more specialised to meet the needs of the user base. Even now, in the mechanical CAD world, a standalone solids modelling package is simply not viable. It must be able to work with any number of other types of packages that are capable of providing highly specific functions, such as FEA or CFD.

In the Windows environment, a group of software companies formed the Design and Modelling Applications Council (DMAC) in early 1995 with the purpose of formulating a methodology for providing interoperability between CAD/CAM software, FEA applications and office productivity tools. The DMAC includes such well known companies as ANSYS, Intergraph, Matra Datavision and SolidWorks.

The DMAC decided to base their solution on Microsoft’s COM (Component Object Model) technology – an operating system based communications medium that allows clients and servers to communicate with one another. The DMAC approach built on top of the COM concept by extending the concept of the 2D OLE commonly used between programs such as Word and Excell to meet the needs of 3D engineering applications.

The extended OLE, called OLE for Design and Modelling (or OLE for D&M), gives the user a live connection between CAD, CAM and CAE applications. The benefit of this approach is that data representing a 3D model can be shared with other applications at runtime, without the need for intermediate file translation. This provides data access, rather than the data exchange which is commonly used today.

Since no data translation actually takes place, there will be no loss of high level data such as features and no need to track the changing data formats that are used. The OLE solution also allows a link with the 3D model to be maintained between heterogeneous systems, so it is possible to query data in a `live’ fashion. Additional functionality, associated with the data at runtime, can also be obtained. For example, designers could be notified the moment at which changes occur.

OLE for D&M is itself a set of custom Component Object Model (COM) interface specifications. Through these interfaces, an application makes its native design and modelling capabilities transparently available to other OLE for D&M-aware software.

OLE for D&M specifies a standard set of geometry and topology interfaces for all applications. It supports embedding, display, and in-place activation, as well as access and control of model geometry and topology through the native design. Although model geometry is readily accessible to OLE for D&M programs, changes can only be made through the original design tool. Model accuracy, precision, and scale are always maintained as designed. And because COM and Distributed COM (DCOM) share programming models, remote applications and distributed design teams can also be supported.

Modelling applications use 3D entities and define relationships between these entities. Manipulations of one entity may require information about another entity to produce or maintain the correct relationship. Geometric relationships are the most obvious example, but modeling applications are not limited to this. To provide interoperability between modelling applications, OLE interfaces have been defined to allow for the manipulation of three-dimensional objects and to allow an object to be in-place edited in the context of its overall model.

Current specifications, program header files, and documentation can be downloaded free of charge directly from the DMAC worldwide web site at www.dmac.org. The DMAC encourages future enhancements and extensions. Two extensions to OLE for D&M, including support for non-manifold topology and a generic add-in mechanism, are currently being considered.

The effectiveness of the approach was demonstrated at a recent technology preview in London. There, the interoperability of several packages from vendors such as ANSYS, Delcam, Intergraph, Pathtrace, and SolidWorks, was shown. In the demonstration, the Pathtrace software directly accessed the Integraph SolidWorks geometry and topology, without going through an intermediate translation step.

There has been a lot of discussion between the companies on what part of the OLE for D&M specification should be required by vendors supporting the standard and what should not be required. In reality, this comes down to how much of the specification is actually required by a given program.

Nevertheless, the DMAC is attempting to identify a means by which compatible products can be identified. It may be that, in the future, a compatibility certification will emerge to classify which programs adhere to the standard, but that probably will not happen until after software applications begin shipping.

{{DMACWeb site: http://www.dmac.orgEmail: dmac-exec@list.intergraph.com}}

{{Microsoft EuropeTel: France + 33 1 46 35 10 10Enter 471}}

{{ANSYS (Strucom)Tel: 0181 983 3999Enter 472}}

{{IntergraphTel: Swindon (01793) 619999Enter 473}}

{{Matra DatavisionTel: Coventry (01203) 693939Enter 474}}

{{SolidWorksTel: Luton Hoo (01582) 431166Enter 475}}

{{PathtraceTel: Reading (01189) 756084Enter 476}}