buildingSMART Forums

LOD and IFC equivalent?


I understand that LODs (level of detail / development / design / whatever) are rather loosely defined, but it does serve a useful primary purpose - that at different stages of the design, BIM elements have varying levels of “resolution”. This information is useful, because right now, given a vanilla BIM model in practically any format (not just IFC), it is impossible for anyone to know how accurate that model is and what they can trust. It also doesn’t help that programs like Revit don’t understand the concept of NULL attribute value = don’t export, and tend to put a bunch of properties in there that may or may not be audited. This is bad - because architects don’t know what is resolved and what isn’t, QSes may not know how much error could be in the costing, shop drawers might not know what is ready and what isn’t, etc.

Does IFC have any concept following the premise of an LOD? i.e. that an element can be very resolved, or just schematic?



I absolutely agree that it’s a problem that you cant see the difference between a sketch and a finished designed element. But is this not solved with using classifications? I think that by using classifications you easily can adopt to your local standard(s). You also can make your viewer software display the classification in a way that fits your need.

Is there any way you think using classification doe’s not fill your need?



You are correct. Using an IfcClassification does fulfill the requirements.

Consider this solved.



I think that’s why MVD (IFC data filter) and validation according to particular MVD is very important, to get ONLY required data for some particular purpose.



Hmm, I think MVD and LOD are two different things: MVD is whether or not the model is suitable for a usecase, LOD is how reliable the current state of data is in the model.



Currently there is not a complete classification to solve the issues related to LoD (which has lot of definitions)
But it seem that some classifications like CoClass have started to focus on it

Another issue is that “all classifications don’t support granular assets” this is why I introduced a concept that maybe IFC, IFD, and other groups focus on this “important” issue



MVD is not alternative to LOD.
For example using ReferenceView you can provide very different levels of details for geometry representations, from boxes to photo-quality with textures.
I do not think we have now LOD inside IFC, but you can use external specification.

IFC has one restriction here - only one Body representation. Some time ago I raised the question should not we allow more then one representation for Body to keep different LODs (or aspects) in one model.



IFC offers more than one shape representation.



but only one representation identifier body