The view for 'Arch. design >> Quantities take off / cost estimating' defines the subset of the IFC model that is used for transferring data from architectural design applications to quantity takeoff and cost estimating applications.
Architectural applications and quantity takeoff applications deal with the same objects (e.g. walls, doors and windows), but the information content for those objects in the applications are quite different. Architectural applications see the world though graphics and the focus has been to produce drawings that can be understood by other people, Quantity takeoff applications are not necessarily interested in any graphics (although some of the more advanced begin to be), instead their focus is in the information content of the building elements. In the IFC model graphics is a vehicle to transfer some of that information content (attribute driven geometry), but most information is exchanged using other mechanisms.
Because of this difference in the applications they do not share the same view of the building objects. An architectural application is interested in the aspects of e.g. a wall that are needed to display its graphics correctly, this might include the material layers and their materials. A quantity takeoff application takes that same wall, but from a different perspective - it assigns actual material, work tasks and labor to the wall to get the price for that wall. In the near future (if ever) the IFC model will not be able to provide both views of that wall, instead we fall back to the method of giving the wall a type and only exchanging the type information through IFCs. Both applications have their own understanding what that type means and they now internally what to do with it. Since the details of the type are not communicated through IFCs this has to happen somewhere else, luckily agreeing on the types is already a common practice in building projects today.
In addition to the actual building elements the IFCs have a lot of information about the relationships between the different building elements. There is support for containment, referencing, grouping and many kinds of specialized relationships such as the relationship between spaces and their boundaries. Although these relationships don't show up in the actual cost estimates they are valuable information for structuring and deriving information. Using these relationships the quantity takeoff applications can e.g. deduct the area of opening from walls or deal with wall connections.
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Copyright © 2000 VTT Building Technology
Author: Jiri Hietanen (jiri.hietanen@qpartner.com)
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