Re: workable IFC-RDF conversion?

Hi Nicolas, thanks for the info!
That's the IfcEngine by rdf.bg, right? And I see the older Zhang approach
does the same.
Nata, it converts to one of:

   - 3D meshes (using "TIN Z..."),
   - Axis Aligned Bounding Box (using "POLYHEDRALSURFACE Z..."),
   - Minimum Volume Bounding Box (using "POLYHEDRALSURFACE Z...").

Unfortunately I won't be at LDAC this year. But I'll be at the Digital
Building Permit (DBP) conference until the end of this week,
where the ACCORD and CHEK projects will have a discussion on this and
related issues.

Thomas Krijnen emailed with his approach,
TUDelft has another approach,
there's Oraskari's IFCtoLBD ...

As Thomas said: it would be nice if the community can settle on some
"standardized" approach.
I hope we can discuss this and 2 more things at the DBP with OGC and others:

   - CityGML RDF representation, with similar concerns: how to capture
   geometry in literals, and how to avoid using "ADE" classes and props for
   extensibility
   - INSPIRE PLU  RDF representation (that's for land-use)

The IFC-RDF approach should align with GeoSPARQL as much as possible.
The main issue with GeoSPARQL is the lack of 3D. It can store Z and M
coordinates (for linear referencing) but doesn't do anything with them.
So we also need to work out useful cases, as you write, relating to LOD1,
LOD2, LOD2.5...

> SVG, GLTF

I think that OpenCascades is also used a lot.
Such a format is great for full model visualization.
There's no harm in keeping multiple representations of the same BIM,
and the question/trick is which aspects of a full geometry are most
important for the specific use cases.

Thanks Nicolas!

On Mon, Apr 15, 2024 at 2:57 PM BUS Nicolas <nicolas.bus@cstb.fr> wrote:

> Hi Vladmir,
>
> We use an IFC renderer (https://github.com/opensourceBIM/IfcEngine) to
> convert IFC implicit geometry to explicit vertexes (B-REP) and then
> serialize it in WKT.
> This approach has been inspired by Ruben de Laat and Chi Zang / Eindhoven
> University works (
> https://pure.tue.nl/ws/portalfiles/portal/117493668/20190311_Zhang.pdf ,
> https://github.com/BenzclyZhang/IFC-to-WKT_Converter)
> IfcOpenShell can also be used to extract geometry (
> https://ifcopenshell.org/ )
> From our point of view RDF geometry Level Of Detail has to be adapted to
> use case needs : 2D WKT for floorplan based use cases, bounding box for LOD
> 100, 2.5D (WKT polygon + height) or 3D for higher LODs
> We only use RDF for inference purposes and still prefer SVG or GLTF for 2D
> or 3D web rendering by using (eveBIM https://www.evebim.fr/telechargement or
> IfcOpenSHell).
>
> Hope that helps
>
> Will you attend LDAC 2024 conference this year ?
>
> Regards,
> Nicolas
>
>
>
>
>
> ------------------------------
> *De :* Vladimir Alexiev <vladimir.alexiev@ontotext.com>
> *Envoyé :* dimanche 14 avril 2024 12:12
> *À :* public-lbd@w3.org <public-lbd@w3.org>
> *Objet :* workable IFC-RDF conversion?
>
> Hi everyone!
> What do you use to convert IFC to RDF with workable geometries?
> Representing geometries with individual triples (eg EXPRESS lists, as
> IfcOwl does) is imho not workable.
>
> We've tried IFCtoLBD but there are various issues
> - see https://github.com/jyrkioraskari/IFCtoLBD/issues/106 for a diagram
> - see https://github.com/jyrkioraskari/IFCtoLBD/issues/99 for a list
>
> Thanks in advance!
>