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.

  

[Laszlo Nagy]

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?

[MASz]

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.

  

[Laszlo Nagy]

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.

[MASz]

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.

[mthd]

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 ?

[MASz]

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.

[MASz]

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.

[mthd]

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.

[mthd]

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.