IFC notdefined userdefined意思

NOTDEFINED is for when you don’t know what the predefined type is going to be yet (for early stage design when you don’t know what the Predefined Type will be). Example you know it’s a boiler but you have no idea if it’s steam or water. Note, you actually use the value NOTDEFINED.

in most cases, the “userdefined” value is included in an enumeration for a more speficic type, e.g. IfcBeamTypeEnum. Here the following rule applies:

1. the user can classifiy the beam in his/her design by declaring it as IfcBeam (often done automatically by the software) and add the value from the type enumeration, e.g. JOIST, this declares the model element to be more specifically a joint (by using the enumerator JOIST)
2. the user can classifiy the beam in his/her design by declaring it as IfcBeam (often done automatically by the software) and add the value from the type enumeration USERDEFINED. Then he/she has to fill in an own value, e.g. “my favoured beam”. This will be exported as ObjectType in the IFC file and provides a user defined typing of the beam

so essentially the combination of USERDEFINED and the user value stored in ObjectType allows for an dynamic extension of the available types in IFC. It can also be used today in infrastruction to added own types without waiting for the new extensions of IFC5.

https://forums.buildingsmart.org/t/userdefined-enumeration/214

https://bimblog.bondbryan.co.uk/ifc-industry-foundation-classes-an-introduction-for-autodesk-revit-users/#more-7365

https://bimblog.bondbryan.co.uk/ifc-industry-foundation-classes-predefined-types-in-autodesk-revit/

IFC notdefined userdefined意思

原文：https://www.cnblogs.com/hao1997/p/14884342.html