The convergence of CAD standards Presented By: Waleed Abdelaziz Kandil By: Jerry Laiserin, FAIA Web Address: T O P I C 92 Date: APRIL 2002

CAD Standards Muddle In an ideal world, a CAD standard would be just what the name implies: a single set of rules and procedures for documenting and conveying building design information regardless of the software used to create it or the medium in which it is viewed. But in the real world, there are multiple, overlapping standards, each of which addresses a different set of issues regarding the organization and appearance of CAD files and the sharing of information with non-CAD applications. Recent advances among standard-setting organizations offer renewed hope for more widespread adoption of existing standards, convergence of standards, and perhaps even unification of the various standards frameworks.

Who carries it out? The primary players driving this integration are: 1- The National CAD Standard (NCS), produced under the auspices of the National Institute of Building Sciences (NIBS) in Washington, D.C. 1- The National CAD Standard (NCS), produced under the auspices of the National Institute of Building Sciences (NIBS) in Washington, D.C. 2- The Industry Foundation Classes (IFCs), developed by the International Alliance for Interoperability (IAI), across the Potomac River in Alexandria, Virginia 2- The Industry Foundation Classes (IFCs), developed by the International Alliance for Interoperability (IAI), across the Potomac River in Alexandria, Virginia

Drawn and quartered The NCS is the result of a convergence among three previously independent standard-setting efforts: 1- The AIA’s CAD Layer Guidelines (CLG). 1- The AIA’s CAD Layer Guidelines (CLG). 2- The Construction Specification Institute’s (CSI) Uniform Drawing System (UDS). 2- The Construction Specification Institute’s (CSI) Uniform Drawing System (UDS). 3- The Department of Defense’s Tri-Services CAD Center’s plotting standards. 3- The Department of Defense’s Tri-Services CAD Center’s plotting standards. Collectively, these components define how design files are organized internally (CLG); what goes into a drawing, how drawings are aggregated onto sheets, and sheets into sets (UDS); and how the digital components are printed or plotted. Collectively, these components define how design files are organized internally (CLG); what goes into a drawing, how drawings are aggregated onto sheets, and sheets into sets (UDS); and how the digital components are printed or plotted.

Version 3 of the standard will be available later this year and will include new terms, abbreviations, and layers from architecture-related disciplines such as civil engineering, piping, communications, and so forth, as well as a new administration section that clarifies many optional components for conformity to the standard. According to Alexander “Sandy” Shaw, who coordinates NCS activities for NIBS, these incremental improvements show the maturity of NCS “in the 2D organizational direction.” He adds, “We will continue to reach out to related disciplines to expand the usefulness of the 2D information; however, we’re also looking beyond 2D toward objects and the facility lifecycle information model.” Having the National CAD Standard built into CAD software, as shown here in ArchiCAD, automates drawing tasks such as title blocks and sheet titles, and ensures coordination and consistency of detail and sheet formats.

Object lessons CAD objects represent a new, more intelligent representation of buildings and building components. The real power of objects lies in their ability to present virtual buildings. CAD objects have attributes and behaviors, such as the handedness and swing of a door. Interoperability among different programs is far more problematic for complex CAD objects than it is for simple 2D lines. This is where IFCs come in: a system of definitions for classes of objects, such as doors, walls, and stairs. If two or more programs, such as space-planning software, a CAD tool, and a cost-estimating package, all comply with the same IFC standard, then they can use and operate on each other’s model data. a system of definitions for classes of objects, such as doors, walls, and stairs. If two or more programs, such as space-planning software, a CAD tool, and a cost-estimating package, all comply with the same IFC standard, then they can use and operate on each other’s model data.

IAI has released several versions of IFCs. While many of IAI’s 600-plus member software firms chose to wait for the most recent IFC 2.x before integrating the standard into their wares. a significant number of IAI members, operating separately under the banner of Building Lifecycle Interoperable Software (BLIS), chose to get a head start by incorporating the earlier IFC 2.0 standard into their products. For example, a space-planning spreadsheet in Microsoft Excel can be converted to a simple floor plan in Microsoft Visio and then turned into a 3D object CAD model in Graphisoft’s ArchiCAD—all through the interoperability features of IFC 2.0, without file conversions or reentry of data. A New IFCs ArchiCAD is the first product to implement and integrate both the object-based IFC 2.0 standard and the 2D-based National CAD Standard. a trend likely to be followed by other vendors that have recently committed to IFC 2.x.

Playing tag Because IFCs support the ability to move data via “tags”, the AIA foresee an opportunity to add XML tags to NCS drawing entities so they can be integrated more easily with IFCs. Owners still have to confront the dominance of legacy information—2D drawings for hundreds of millions of square feet of space. Owners still have to confront the dominance of legacy information—2D drawings for hundreds of millions of square feet of space. NCS provides the continuity and consistency for drawings, but companies moving to object models like IFC need to manage their migration and be committed to maintaining the extended value of the model data. Using some form of XML will smooth that process. It is hopeful that intermediate steps such as XML will help bring the NCS and IFCs closer together.