topic Revit IFC to Archicad is fundamentally flawed in Collaboration with other software

Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 01:28:56 GMT

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.

Re: Revit IFC to Archicad is fundamentally flawed

Laszlo Nagy — Mon, 26 Feb 2024 01:34:40 GMT

It should not be a problem if Revit Walls are converted to Archicad Library Parts when the imported IFC geometry is used only as reference, as per recommendations.

When the model is far from Origin, do you use the Survey Point in the IFc exchange process?

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Mon, 26 Feb 2024 23:18:42 GMT

I do not know what you are suggesting with your first line. Why would I only be using it as a reference? If it a survey, then I need to use it as a base that can document correctly and be modified. The GSMs are not editable, they do not display correctly in plan, they destroy windows and doors, etc. It is generally destructive. In the real world, Revit surveys are becoming more common place and Archicad is not equipped to deal with it.

My process for the origin is as follows:

Origin for Archicad

In Revit standard IFC export, Project Origin: Project base point
In Archicad, Match Archicad Project Origin with: IFC Global Origin

I've attached screenshots. You have several coordinate base options in the vanilla exporter as compared to the add-in.

Re: Revit IFC to Archicad is fundamentally flawed

Laszlo Nagy — Mon, 26 Feb 2024 23:29:50 GMT

It is generally recommended to use IFC from other software as reference.

The simple reason is there are so many applications, all with their own philosophy, concepts, geometric capabilities, data structure, etc. that it is unrealistic to expect all native geometry from one application to convert to the native geometry of the other application through IFC exchange.

For example, Walls in Revit can be double curved Walls. Archicad Walls do not have this capability. So when an IFC from Revit contains such a geometry, it cannot be converted to an Archicad Wall. So, it is converted to one of two things: Morph or Object (Library Part). Both can conserve the geometry.

And there are hundreds of these cases for each pair of applications where you have these differences.

This is why the industry realized the workflow of "Model stuff in App A, send it to App B through IFC, and continue modeling it in App B" is not realistic.

Maybe a vertical rectangular Column in Revit can be converted to a vertical rectangular Column in Archicad through IFC because both applications support that type of geometry. But as I said, in many cases, a lot of geometry types cannot be converted to native elements. This is why, as a general guideline, it is recommended to use IFCs from other applications as reference only.

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 00:53:36 GMT

Thanks for the clarity.

The biggest concern here is Revit. I mean, there specifically is Archicad Connection plugin for Autodesk Revit. The advertising suggests it should be usable and editable, where exactly does it say "only for reference"? This feels like a contradiction. While I don't expect double curved walls to work, clearly there are workarounds to get the wall profiles to work. I have had to make it work. The possibility to support certain BREP walls was raised. With that feature alone, it would be a lot better. Those NURBS windows and objects are a different story, but maybe that could work better with IFC4?

It is pretty disheartening otherwise to essentially be told that there will not be any solution to this, that if I get a Revit survey then I am my own. I am very hesitant to recommend that anyone uses Archicad given things like this. Many would be better off using Revit.

The link RVT feature could also be developed further if Graphisoft's attitude is that IFC is unworkable. It does have potential, especially the way it is handling NURBS. That one is specifically as a non-editable reference as opposed to IFC from what I can see.

Re: Revit IFC to Archicad is fundamentally flawed

mthd — Tue, 27 Feb 2024 01:14:02 GMT

Hi @MASz, I haven’t needed to import a 3D Revit file from an engineer just yet but I was also under the impression from that advertisement that it was possible with an add on ? ? ?

Here is the advertisement for AC25 about collaboration with Revit & Solibri.

https://www.youtube.com/watch?v=qLNZahp8z-g

Anyone able to give us some more insight about these methods ?

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 01:25:48 GMT

The video shows hotlinking an RVT file. It is not editable as everything comes in as an object, i.e. elements such as walls and slabs are all converted to objects. That's just an inbuilt feature of Archicad.

The add-in is here: https://graphisoft.com/downloads/interoperability

The manual covers the extra features. However, it does not solve any of the geometry problems I have discussed. The developer response says that it is correcting the native IFC export, so then the native IFC export geometry is bad then so too will be the geometry coming from the add-in. But I can't recommend the add-in if the origin needs to be controlled. There is still no indication of whether this control will be added, but you do lose a lot of other settings as well.

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 01:38:07 GMT

Having another look at the video, it is pretty misleading.

It shows hotlinking an RVT file. Then cuts to editing a wall. You cannot actually do this. Perhaps they redrew a wall.

Re: Revit IFC to Archicad is fundamentally flawed

mthd — Tue, 27 Feb 2024 01:38:48 GMT

Thank you for helping me to understand better the capabilities of 3D import from Revit. Looks like IFC is the preferred method if we want things to be edible in 3D but with those limitations that you outlined above. I will keep that in mind if I ever have to import a 3D model from from Revit.

Re: Revit IFC to Archicad is fundamentally flawed

mthd — Tue, 27 Feb 2024 01:50:07 GMT

On the roadmap, under the research section, it appears that IFC 4.3 may help but that is yet future ?

Doing the extra work to get the 3D imported model correct is all we can do for now.

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 17:01:37 GMT

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.

Re: Revit IFC to Archicad is fundamentally flawed

MASz — Tue, 27 Feb 2024 09:05:04 GMT

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.

Re: Revit IFC to Archicad is fundamentally flawed

stefan — Tue, 27 Feb 2024 09:06:39 GMT

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/index.htm

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.