Revit IFC to Archicad is fundamentally flawed

[MASz]

Going from Revit to Archicad with IFC is a seriously flawed process. The result is barely usable without a lot of work to fix it. I have raised this previously with the developers.

One of the biggest issues is that certain walls from Revit are being converted to .gsm objects. This makes them useless, you have to redraw them. This tends to happen with walls that use profiles.

The response from the developer is:
"It seems Revit exports these kinds of walls as BREPs and since our AddIn is doing corrections on the native Revit IFC export itself we cannot resolve this issue. We will check on our side if we somehow could generate native walls from BREPs in some cases, but the issue in general I think is a Revit export issue, not an Archicad import one."

They then closed the ticket and never followed up about the checking on their side. The response from my local support team is that it is a software limitation and they are unable to help further.

My suggestion was to take these walls and recreate them as walls with SEO - this is the process I have to do manually myself. I also pointed that the walls correctly import in other software such as VisualARQ for Rhino. These suggestions did not go anywhere.

I can't even use the Add-In for Revit, I can't set the Coordinate Base as I can in the native exporter. If the origin is very far away in Revit, then this will bug the import into Archicad. I have raised this and it was not addressed. While the Add-In is useful in some ways, it does not fix the issues with geometry.

The other issue is that NURBS objects mesh badly and become low poly, which is an issue with the exporter. Unfortunately my only workaround has been to hotlink the RVT, then copy certain objects across. There is supposed to be the level of detail for element geometry, but in my experience this setting doesn't really do much. Everything is still low poly. This can look awful in particular for elevations.

In summary my recommended workflow from Revit IFC Survey is:

• Open IFC file
• Save
• Find select and delete all objects
• Save separately
• Reconstruct walls etc as needed by editing the Revit file, creating new IFCs , copying problem walls and using SEOs.

For high resolution objects:

• Hotlink Revit file
• Break link
• Copy objects as needed as needed across

I can see the roadmap mentions no plans to improve IFC. The only thing mentioned is "Support of IFC 4.3" which I doubt will be very useful in this case. In my experience, using IFC4 between Revit and Archicad creates even more .gsm objects and problems.

In regards to documentation, it is insufficient as well. I had to figure out a lot of this on my own. I could not find it covered anywhere.

So, what is going on here? Is this in the simply "too difficult to address" pile? It's a huge problem for me since so many companies in Australia are using Revit. I am even getting survey files in Revit IFC now. It really cuts out Archicad from the entire process. To basically see no interest from Graphisoft to try and fix the problems is so frustrating. It presents me with a dead end and I cannot progress or push on this issue further.

I am wondering what the experience is from other users, since I can't imagine that anyone who has to go through Revit to Archicad is having an easy time at all.

  

[MASz]

The add-in manual states the following:

"Although both Archicad and Revit support the import of IFC4 files, IFC2x3 Coordination View 2.0 is
currently the latest worldwide-certified IFC standard and the recommended IFC version for model sharing
among different disciplines and systems. So, this Add-In imports only IFC2x3 files.

I have tried using IFC4 Design Transfer View, which does import NURBS but also causes BREP problems with walls that would otherwise be fine (see attached, BREPS in blue)

And yes, the best bet is to import IFC and try to modify anything that comes in converted. You do need to take a close look. You may have to make changes in Revit specifically for this purpose, and then modify in Archicad. I have not worked with any Revit engineering files, so your mileage may vary.

 

[MASz]

I think one idea would be to add a system that works like Revit's wall profiles: https://help.autodesk.com/view/RVT/2023/ENU/?guid=GUID-F3B8DD5E-5380-45C1-B0D6-E6B081224E63

That way, when IFC is imported from Revit that contains such elements, it could just work natively rather than having to create SEOs or anything like that.

[stefan]

IFC2x3 Coordination View 2.0 is still widely used. And it has some support for extrusions upon export, but every time you have geometry that is not a strict extruded shape, it will become BREP. This is try for Archicad IFC export and for Revit IFC export.

The purpose of this conversion is coordination and referencing, not handing over the design.

This is the Certified MVD most applications possess.

IFC4 Reference View is an updated version of IFC2x3 CV2.0, but more strict constraints on the type of geometry that is exported.

https://standards.buildingsmart.org/MVD/RELEASE/IFC4/ADD2_TC1/RV1_2/HTML/schema/views/reference-view...

Common characteristics of the workflow using reference models are:

• The full parametric behaviour, and thereby the intellectual engineering property, remains with the originator
• The receiver of the IFC4 Reference View model has access to the full model content
• The receiver of the IFC4 Reference View is not supposed to modify the model

This is the certified MVD for IFC4 that some applications have.

The first main objective of the IFC4 Reference View is to enable the exchange of highly accurate, not non-parametric, geometric representations of the model elements. Each model element is placed directly or indirectly within the project coordinate system, defining its own object coordinate system. The geometric representation items describing its shape are positioned within this object coordinate system.

In order to minimize the effort for receiving and interpreting the geometic representations by the receiving software systems, in terms of development effort, processing power and loading times, the complexity and variety of geometric models has been minimized for the IFC4 Reference View.

In scope of geometric shape representations of the 3D body geometry of physical and spatial elements are the following concept templates:

• "Body Tessellation Geometry", using tessellated geometry in form of triangulated tessellations for describing the body shape of the model element;
• "Body SweptSolid Geometry"; using extruded solid geometry or revolved solid geometry for describing the body shape of the model element;
• "Body AdvancedSweptSolid Geometry"; using advanced swept solid geometry of circular cross sections for describing the body shape of the model element, only the swept disk solid is in scope;

It is the default geometric representation of all model elements, allowing for a surface model representation with an indicator for closed shells (and therefore true volumes). The tessellated representation offers a very efficient way of exchanging 3D shape date, both for data set sizes and for processing time. Optionally the face normals can be exchanged as well.

Since curved shapes would lead to very densely triangulated areas, the following swept solid based representations are also in scope of the IFC4 Reference View, balancing simplicity and compactness of representation:

All other geometric models are out of scope of the IFC4 Reference View, in particular Boolean operations required for Constructive Solid Geometry CSG.

And finally, the IFC4 Design Transfer View supports more editable geometric definitions. However, this has to be set upon export from the source Revit file. If you just received an IFC from somebody and it's not exported as Design Transfer, you cannot do anything about it.