CreateContext fails inconsistently across machines for small extruded profiles

[A-Shawqi]

Hello,

I have a few IFC files that process fine and generate wexBIM successfully on my local development Windows 11 machine, but fail on other machines with the same XBIM version. The geometry engine throws an error when processing IfcExtrudedAreaSolid entities that have profiles with very small coordinates.

The failure happens during CreateContext() when processing some IfcExtrudedAreaSolid entities that have very small profile coordinates (sub-millimeter values). On the local dev machine, this works fine, but on other machines, it throws an exception and stops the whole geometry creation and doesn't gerate wexBIM.

I’ve uploaded a sample IFC file that reproduces the issue on some machines:

XBIM-Issue-Sample.ifc

There are two example problematic entities in the file: #2173596 and #2182386.

Environment

Failing machines:

• Windows 11 and Windows Server 2022
• .NET 6.0

XBIM Assembly Versions

• Xbim.Geometry.Abstractions: 6.0.0.0
• Xbim.Geometry.Engine.Interop: 6.0.0.0
• Xbim.Common: 6.0.0.0
• Xbim.ModelGeometry.Scene: 6.0.0.0
• Xbim.Tessellator: 6.0.0.0

Full Stack Trace From Log

System.Exception: General Error Creating IfcExtrudedAreaSolid, #2173596
   at Xbim.Geometry.XbimGeometryCreator.Create(IIfcGeometricRepresentationItem geomRep, 
      IIfcAxis2Placement3D objectLocation, ILogger __unnamed002) 
      in E:\build_os\_work\6\s\Xbim.Geometry.Engine\XbimGeometryCreator.cpp:line 352
   at Xbim.ModelGeometry.Scene.Xbim3DModelContext.<>c__DisplayClass42_0.<WriteShapeGeometries>b__0(Int32 shapeId)
   at System.Threading.Tasks.Parallel.<>c__DisplayClass44_0`2.<PartitionerForEachWorker>b__1(...)
--- End of stack trace from previous location ---
   ...
Xbim.Common.Exceptions.XbimException: Processing halted due to model error, see logs
 ---> System.AggregateException: One or more errors occurred.
      (General Error Creating IfcExtrudedAreaSolid, #2173596)

Problematic IFC Geometry

Looking at the IFC data, the failing entity uses a profile with very small coordinate values (around 0.0002–0.0004 meters):

#9=IFCDIRECTION((0.,0.,1.));
#2173596=IFCEXTRUDEDAREASOLID(#2173592,#2173595,#9,0.10000000000000323);
#2173592=IFCARBITRARYCLOSEDPROFILEDEF(.AREA.,'WALL SKIRTING 100',#2173591);
#2173591=IFCINDEXEDPOLYCURVE(#2173590,$,.F.);
#2173590=IFCCARTESIANPOINTLIST2D(
  ((-0.00044555529947738125,-0.00022277764973369045),
   ( 0.00022277764974193906,-0.00022277764973369045),
   ( 0.00022277764974299011, 0.00044555529947703089),
   (-0.00044555529947738125,-0.00022277764973369045))
);
#2173595=IFCAXIS2PLACEMENT3D(#2173593,#9,#2173594);
#2173593=IFCCARTESIANPOINT((0.00041523525350357888,0.6766566561126065,0.));
#2173594=IFCDIRECTION((0.12132557005372908,0.99261276742299553,0.));

The profile ends up being a very small triangular / near-degenerate shape.

What I Already Tried

• Forcing single-threaded execution (context.MaxThreads = 1) → still fails
• Trying V5 engine mode using AddGeometryServices(builder=>builder.SetVersion(Xbim.Geometry.Abstractions.XGeometryEngineVersion.V5))→ still fails
• Double-checked that both machines use the same XBIM NuGet packages versions

Questions

1. Is there a minimum coordinate size or profile area that the geometry engine requires?

2. It’s strange that some machine handles this fine, while other machines don’t, Any idea what could be the reason?

3. Is there a way to configure CreateContext() to skip problematic shapes and continue processing the rest of the model instead of throwing and stopping everything?

4. Could this be related to Visual C++ runtime, OpenCASCADE, or native dependency differences between the machines?

5. Are there any known workarounds for IFC files that contain extremely small geometry like this?

Any guidance would be really appreciated. Happy to provide more details if needed.

[andyward]

My guess is this will come down to ModelFactor Precision which is what handles minimum coordinate size.

I have a recollection that MemoryModel and EsentModel handle the default precisions differently, and this being a large model may trigger the use of Esent. Can you try forcing the use of memory Model? IfcStore.Open(...) has an overload parameter to do this.

The precision on this model is 1.0000000000000001E-05. try setting it to 1.E-05 ... I'm not sure if that tiny FP may be causing issues:

#22=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.0000000000000001E-05,#20,#21);

Detail: You've already identified there are degenerate shapes in there. This can create circumstances where the OpenCASCADE code exits uncleanly which may give these kind of transient crash. Unfortunately once you've got an unclean stack it's hard to recover. We have to trap these edge cases in the managed layers.

To help diagnose further can you provide the actual (Package) versions of xbim Geometry/Essentials you're using (rather than teh fixed 6.0.0.0 assembly version)?

[A-Shawqi]

Hi @andyward, thanks so much for the detailed response and suggestions!

I tried what you mentioned and I'm using version 6.3.873-netcore of the XBIM Geometry package on both machines. One thing I noticed is that even with v6, the Xbim3DModelContext constructor default engineVersion is still v5. When I explicitly set it to v6, some models that were failing now work successfully on all machines.

Unfortunately, a few models still fail on one machine while working fine on another. For example, this model: XBIM-Boolean-Issue.ifc has been running on the XBIM desktop viewer (develop branch) for over a day now - the process hasn't finished or crashed (unlike with v5), but the log shows many of these warnings:

........
BOPAlgo_AlertAcquiredSelfIntersection
BOPAlgo_AlertTooSmallEdge
BOPAlgo_AlertBOPNotAllowed
WARN Boolean cut returned an empty result
WARN GeomScene: #1293961=IfcWall [Contains openings but its basic geometry can not be built, Boolean cut returned an empty result]
WARN Boolean resulting shape is invalid, skipping SimplifyResult()

Interestingly, the same model opens in BIM Collab ZOOM in just a few minutes on the same machine.

A few questions if you have time:

Is there a way to skip or timeout invalid/complex self-intersecting boolean operations in the XBIM context? Or at least have it throw an exception like before rather than hanging?

Could you point me to any machine or software requirements that might affect CreateContext? It works consistently for all these models on one of my dev machines but fails on the server - would help me know what to check/update on the server.

Thanks again for your help!