If something is shown in BIMMeasure and, when selected, the properties associated with it are pre-fixed with “ifc” then the definition of that object / propertyset / prop erty has been subject to many hours of independent and international scrutiny.
The Industry Foundation Classes are platform neutral, open file format specifications to describe building and construction industry modelling data. It enables members of construction teams with different modelling systems to exchange models without the loss of data and functionality (subject to the ability of the ifc exporter and importers).
In relation to BIMMeasure, it is the ifcPropertyDefinition data that are utilised. For common building and construction objects ifc defines hundreds of property sets that are attached to the objects in the model. In addition, custom property sets may be defined by application vendors or end users over and above the ifc definitions.
However the model generating source application may not always fully populate the object BIM Properties so it always a good idea to review the BIM data provided prior to measuring.
In order to prevent ambiguities in BIM Properties the IFC specification also includes "Base Quantities" for a range of, but not all, objects. These Base Quantities have very specific definitions as to what the named property represents. For example, for an ifcBeam:
· GrossWeight: Total gross weight of the beam without add-on parts, not taking into account possible processing features (for example, cut-out's) or opening and recesses.
· NetWeight: Total net weight of the beam without add-on parts, taking into account possible processing features (for example, cut-out's) or opening and recesses.
All ifc compliant modelling systems will support Base Quantities but the option to include the Base Quantity data in an exported .ifc file may be optional.
It is strongly recommend that as part of the project data exchange protocols the Base Quantities are included in the generation of .ifc files. These will then appear in the BIMMeasure Properties as a separate set of data that can be utilised in the BIMMeasure Rule Sets. It should be noted however that not all ifc defined objects have BaseQuantities, even within the same family of objects.
The presence or absence of Base Quantities at a general level is indicated on the Attached Drawings screen when first opening a .ifc file.
If it is indicated that Base Quantities are missing it is recommended that the provider of the .ifc file is asked to reissue it with Base Quantities enabled.