Saturday, 11 August 2012

GH to Archicad (OpenBIM IFC)

With the new release of Archicad v16, it permits me the opportunity to download and test improvements made to IFC support.  This is still in progress, and initially I was a little disappointed, but revisiting a single test case for Constructive Solid Geometry (CSG) or Solid Element Operation as it might be known to Archicad users leads me to confidence and optimism about IFC exchange with Archicad.

So here's the test case that has me excited.  I posted nearly 2 years ago about most software reverting to "coordination" IFC models, primarily faceted breps (meshed surfaces).  Possibly this is acceptable for visualization and clash detection (but not efficiently) but if you want smart models that can be enhanced and edited down stream, IFC is derived from STEP and capable of many advanced and accurate shape representations.  This is also explained in my Technical Paper from last year.

So in two years I've still had no success in other software understanding the CSG steps that can define a gothic arch roof, until now.  I was thrilled to see Archicad v16 import this accurately, which might enable some really exciting project work flows from Grasshopper.  Perspective view doesn't seem to render anything, but isometric does (maybe someone can explain why).

Here's the IFC file if you want to test yourself, and here's the Grasshopper Definition.

The first test I ran also worked quite well.  Archicad doesn't have nurbs (at least yet), so I converted the nurbs curves for the Klein Building slabs into polycurves.  IFC file, Grasshopper Def

Now for some tests with scope for improvement. I tried to import an IFC file with swept beams.  It was pleasing to see the straight beam generate accurate edit handles, but none of the curved beams worked.  IFC4 does not appear to developed, so useful improvements such as cardinal points are not accessible.  IFC file, Grasshopper Def

And the final test for the time being, the waffle structure.  Slabs come in fine, seems to be an orientation issue for the walls.  Geometry looks accurate otherwise.  IFC file, Grasshopper Def

I'm hoping to do some more tests very soon.  If you've comments, suggestions or questions, I look forward to hearing them.