Software strategy: BIM comparison: how does BIM software stack up with the 3D model concept?

CADalyst,  Jan, 2005  by H. Edward Goldberg

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AS SOFTWARE VENDORS PUSH THE BIM (building information modeling) concept, many firms are wondering how the various options stack up against the others. This article attempts to codify the distinctions among the major 3D building modeling applications. As outlined in the November issue of Cadalyst (http://aec.cadalyst.com/aec/article/article Detail.jsp?id=133495), this genre of software uses the concept of working with components such as walls, doors and windows to create a virtual 3D building model from which views and information are extracted. The end result is the production of construction documents that resemble those created by 2D CAD or standard drafting methods, but these are created more quickly and contain information such as quantities, materials and areas that can be used in the construction and management of buildings.

The major BIM software products, in my opinion, are Bentley Architecture, Graphisoft ArchiCAD, VectorWorks ARCHITECT and Autodesk's Revit and Architectural Desktop. This conclusion is based on quantity of installed seats, true object CAD or parametric modeling capability, routines or programming dedicated to the architecture and construction industry and extraction of views and information directly from a 3D model. Note that I am not proficient with all of these programs, but have attempted to compare their capabilities by observing their operation by competent professionals.

BIM software solutions generally divide on two categories: unidirectional vs. bidirectional editing and single-file vs. multifile databases. All of these solutions initially design a 3D model and then extract views, such as elevations and sections, and other information. In a unidirectional approach, manipulating the extracted views and information will generally not automatically change the model or other views. Unidirectional approaches generally keep information in separate document files that are electronically linked, but where changes will not affect the model.

On the other hand, changes to extracted views and information in a bidirectional software, such as Revit, Bentley Architecture, ArchiCAD and VectorWorks ARCHITECT, do affect the model as well as all the other views and information throughout the project. To achieve this result, all information must be interrelated at all times. To create such a permanent interrelationship, the software solution must keep all the information about the project (models, views, sheets, schedules and so forth) in a single database file, or manage relationships between databases in multiple files. Though the bidirectional, single-database concept creates a very efficient operating environment, it also produces a much larger single file than those programs that use the unidirectional, electronically linked file solution. The single file, in the case of Revit and to a lesser extent with ArchiCAD and VectorWorks ARCHITECT, is probably larger than any DGN file or individual DWG file in an Architectural Desktop project, but is likely to be smaller than the total collection of files that make up an Architectural Desktop or MicroStation project. The multi-file approach is inherently more scalable and likely to perform better because it doesn't need to handle the entire model all the time, but it can require a bit more management and care in setting it up. Users need to weigh the pros and cons of each approach to match their needs.

* Graphisoft ArchiCAD

Graphisoft ArchiCAD, introduced in 1984, was the first product among these solutions to create a virtual model. Now in its ninth version, ArchiCAD's bidirectional associative models keep all the data in one PLN file that can hold a 60,000-square-foot building--including all construction documents--in a 30MB file. ArchiCAD uses the GDL (geometric description language) model creation language. GDL contains all the information necessary to completely describe building elements as 2D CAD symbols, 3D models and text specifications for use in drawings, presentations and quantity calculations. The program also ships with the RCC (Richard Creveling database) that can be interpreted by Timberline software to instantly create Level 2 cost estimates.

ArchiCAD is a rare program--VectorWorks ARCHITECT is another--that is offered on the Macintosh as well as Windows platform. This is an excellent BIM program, and because it's been around the longest, it may have the most routines dedicated to architecture and construction. It's very popular in Europe and is used by prolific firms such as Davis Brody Bond in New York and D'Aleo and Associates in Baltimore.

Besides ArchiCAD, Graphisoft offers ArchiFM for facilities management and recently introduced a complete new product line for design/build firms, construction firms, engineering firms and consultants. This product set, which includes GS Constructor 2005 and GS Estimator 2005, allows companies to perform model-based calculations for scheduling, estimating and purchasing and provides a comprehensive platform with which they can manage an entire construction project. Constructor also includes a next-generation MEP modeling environment as well as a structural modeling library.