IFC-compliant workflow

[yorikvanhavre]

Idea: being able to load and save IFC files with minimal or no data loss. while preserving FreeCAD's free modelling paradigms that are not too tied to the IFC structure

Workflow

• Open an IFC file
• Modify some elements
• Save the IFC file
• Only the modified elements are modified, the rest stays the same

Implementation

• The file is imported "the normal way", this is different than BlenderBIM: not supported entities are discarded, and the different import styles of FreeCAD continue to work
• When opening an IFC file, an entry is created in the document meta, referring to the original IFC file, wtih sha hash
• Alternative: The whole IFC file can be embedded?
• IFC objects are created with an "unmodified" tag
• The user modifies, creates objects, etc... normally. For each of them, the "unmodified" tag is removed. Deleted objects are added to some delete log
• When saving to IFC (being the original IFC file or a new one), the original file is read first
• If IFC data is unavailable, or if the sha has changed, the user is warned
• The ifcbin is ran on the file to collect/catalog existing elements
• The existing building structure is collected
• New IFC shape representations are generated
• Existing objects are updated, new objects are created, deleted objects are deleted. Attached shape representation sare collected
• Shape representations are deep-deleted, with elements that only depend on them
• Exported objects are marked as unmodified
• The new hash is stored, or the included IFC content is updated

[brunopostle]

Linking to this discussion on 'Native IFC' definitions for reference: IfcOpenShell/IfcOpenShell#2240

[luzpaz]

Sweet, thanks @brunopostle !

[yorikvanhavre]

To use the new BIM IFC importer where most of the work here is gonna be done, several options:

1. Use latest FreeCAD code, then there is nothing to do (just make sure Preferences -> import/export -> IFC -> multicore is > 0)
2. In Open/Import file dialog, make sure to select "Industry Foundation Classes (BIMWB)" as the importer

[Moult]

I might recommend starting with a smaller scope, like attribute editing :) I'm super keen for this to be a reality!