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Issue with roof coming from Revit

  1. C by Cyril on 5 Nov 2020, edited 13 Nov 2020 # +1 votes

    Hi,

    I encountered an unusual strange issue I don’t know how to fix. I made a BEM model based on Opening Design Aalseth Residence. When I export to IFC it from Revit, roof became :

    • made of thin layers instead of a solid geometry

    • roof are wrongly classified as IfcSlab despite

    <img src="https://community.osarch.org/uploads/editor/ke/0tmqknurxhcb.png" alt="Boat house"

    title="Boat house" width="300" /><img src="https://community.osarch.org/uploads/editor/61/z4d7cncxtuc3.png" alt="Boat house"

title="Boat house" width="300" />

    I have no override anywhere. I tried with IFC 2x3 CV2 and IFC 4 RV and got same result. I opened the IFC in XBIMXplorer and Blender with BIM Addon and get same result so it is really an export issue.

    As anyone ever encountered this issue ?

    This model will be used to showcase BEM analysis I am working on and will be available as Revit file, ArchiCAD file and hopefully when we will found out how to generate IfcRelSpaceBoundary2ndLevel some day as Blender file.

  2. B by Bedson on 5 Nov 2020 #

    If you add a Shared Parameter called IfcExportAs and give it the value of IfcSlab.ROOF then this should correctly classify the element when exported from Revit.

  3. C by Cyril on 5 Nov 2020 #

    @Bedson said:

    If you add a Shared Parameter called IfcExportAs and give it the value of IfcSlab.ROOF then this should correctly classify the element when exported from Revit.

    According to wiki it is hardcoded : https://wiki.osarch.org/index.php?title=Revit_and_IFC_classes but I missed that the roof is decomposed by 2 slabs while main class is IfcRoof as expected.

    The real issue is only on geometry then.

  4. M by Moult on 6 Nov 2020 # +1 votes

    It's been on my to-do list to finish that somewhat empty table on the wiki page - you'll notice roofs are empty. I want to confirm (i.e. by reading the code) exactly what the behaviour is. For example, curtain walls can be treated as roofs, and I need to check the effect of exportByComponents here.

    I'll try and replicate your bug on Monday when I get access to Revit :)

  5. C by Cyril on 6 Nov 2020, edited 6 Nov 2020 #

    Thanks. For info I opened an issue #244 and it include sample files containing the issue.

    Edit : apparently actually an IFC4 RV only issue (I probably did something wrong in my previous tests)

  6. M by Moult on 13 Nov 2020, edited 13 Nov 2020 # +1 votes

    A note that the behaviour for roofs may change when the IFC4 certified version gets released (currently 17 days and counting!)

    See this commit: https://github.com/Autodesk/revit-ifc/commit/64786c58fd6a34254cbf0e292966459334599fa8#diff-533e2b27282abd03f34b4bcb24d70fc76015f0c6534c96b45599a5f17be35af4R212-R216 - see how in RoofExporter.cs it can now export just a roof, without being a slab aggregation.

    I see similar improvements for other categories, like walls, which from skimming through now seems to be able to be assigned to any IFC class.

    This is good news.

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