topic NURBS Export in Revit API Forum

NURBS Export

vilo176 — Fri, 14 May 2021 16:32:00 GMT

Hi Folks,

I'm having a (suspected) issue when trying to export Revit geometry.

Basically, I've a scene with several objects of all kinds, and I want to export them in parametric description.

The problem arrises with RuledFace & HermiteFace.

To export them, I'm using "ExportUtils.GetNurbsSurfaceDataForSurface()" to cast the surface into a NURB like surface.

I've attached 2 screenshots :

"Revit wall.jpg" contains the Revit Wall defined by 2 RuledFace (Front / Back) & 4 PlanarFace (Top / Bottom / Left / Right).

"Exported.jpg" contains the exporter geometry.

Gray faces (Top / Bottom / Left / Right) are good.

Red faces (Front / Back) are what "GetNurbsSurfaceDataForSurface()" gives me for RuledFace, and you can see that they are not well placed.

Am I missing something in "GetNurbsSurfaceDataForSurface()" datas ?

Thanks 😉

Re: NURBS Export

jeremy_tammik — Sat, 15 May 2021 04:16:34 GMT

I cannot tell off-hand what might be causing this. If all else fails, please submit a minimal reproducible case for passing on to the development team for analysis:

https://thebuildingcoder.typepad.com/blog/about-the-author.html#1b

Re: NURBS Export

vilo176 — Sat, 15 May 2021 08:58:30 GMT

I've made another example, here are the new shots + RVT.

Underlying surfaces are filled in gray, and face boundaries are displayed in wireframe.

In case of NURBS surfaces (which are naturally bounded), face boundary must be inside surface (hence the issue here).

The obvious solution would be to stay with a RuledSurface definition (that is good), and not rely on "GetNurbsSurfaceDataForSurface()", but this leads to another issue : there is no guaranty that the reconstructed surface will be exactly the same as Revit ones, because a RuledSurface has to be recomputed.

Re: NURBS Export

vilo176 — Sat, 15 May 2021 09:31:06 GMT

Correction : by exporting directly RuledSurface curves, I have the same issue (boundaries not being inside the surface Min-Max).

So "GetNurbsSurfaceDataForSurface()" is not the problem here.

Re: NURBS Export

vilo176 — Mon, 17 May 2021 10:38:21 GMT

It seams that "degenerated" faces can be identified by "RuledSurface.IsExtruded".

When "IsExtruded == false", face definition (through "GetNurbsSurfaceDataForSurface") is good (i.e. Surface & Edges are lying within the same UV domain).