The concept of parametric objects is central to understanding BIM and its differentiation from traditional 3D objects. Parametric BIM objects are defined as follows:
- Consist of geometric definitions and associated data and rules.
- Geometry is integrated nonredundantly, and allows for no inconsistencies.When an object is shown in 3D, the shape cannot be represented internallyredundantly, for example, as multiple 2D views. A plan and elevation of agiven object must always be consistent. Dimensions cannot be “fudged.”
- Parametric rules for objects automatically modify associated geometrieswhen inserted into a building model or when changes are made toassociated objects. For example, a door will fi t automatically into a wall,a light switch will automatically locate next to the proper side of the door, awall will automatically resize itself to butt to a ceiling or roof, and so forth.
- Objects can be defined at different levels of aggregation, so we can definea wall as well as its related components. Objects can be defi ned and managed at any number of hierarchy levels. For example, if the weight of awall subcomponent changes, the weight of the wall should also change.
- Objects’ rules can identify when a particular change violates object feasibility regarding size, manufacturability, and so forth.
- Objects have the ability to link to or receive, broadcast, or export setsof attributes, for example, structural materials, acoustic data, energy data,and the like, to other applications and models.
Technologies that allow users to produce building models that consist of
parametric objects are considered BIM authoring tools.
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