topic How to facet AcDbSubDMesh objects? in ObjectARX Forum

How to facet AcDbSubDMesh objects?

Anonymous — Tue, 01 May 2012 12:02:46 GMT

AcDbSubDMesh objects are produced by the MESH command in autocad 2010 upwards. I wonder if anyone can let me know how to get at the underlying geometry of the object, to produce an array of triangles or polygons representing the object?

Thanks

Malcolm

Re: How to facet AcDbSubDMesh objects?

Alexander.Rivilis — Wed, 02 May 2012 04:54:13 GMT

What about using method explode of class AcDbSubDMesh?

Re: How to facet AcDbSubDMesh objects?

adam.nagy — Wed, 02 May 2012 10:29:01 GMT

Hi there,

I have just written a blog post that also might be of help:

http://adndevblog.typepad.com/autocad/2012/05/facet-subd-mesh.html

Cheers,

Adam Nagy

Autodesk Developer Network

Re: How to facet AcDbSubDMesh objects?

Anonymous — Wed, 02 May 2012 10:41:32 GMT

I think I can answer my own question. There seem to be a couple of ways to go. The first is pretty direct:

Given an AcDbEntity *pEnt pointer:

AcDbSubDMesh *pMesh=(AcDbSubDMesh *)pEnt;

AcGePoint3dArray vertexArray;
AcArray<Adesk::Int32> faceArray;

Acad::ErrorStatus es = pMesh->getFaceArray(faceArray);
if(es==Acad::eOk){
es=pMesh->getVertices(vertexArray);
}

And then walk through the faceArray and Vertex array to extract the geometry. The above however doesn't do any smoothing, so that you end up with a large number of elements even for simple geometry. For example, for a simple default cube, this gives 54 (or 56 can't quite remember) faces. I don't know if someone has any suggestions on this.

In order to reduce the face count, all I can come up with is to go via a solid, and choosing the appropriate bConvertAsSmooth and optimize flags:

AcDbSubDMesh *pMesh=(AcDbSubDMesh *)pEnt;

AcDb3dSolid *pSolid=NULL;
pMesh->convertToSolid(false,true,pSolid);

if(pMesh!=NULL){

AcDbFaceterSettings faceter;
AcGePoint3dArray vertexArray;

AcArray<Adesk::Int32> faceArray;
AcGiFaceData* faceData=NULL;

Acad::ErrorStatus es=acdbGetObjectMesh(pSolid,&faceter,vertexArray,faceArray,faceData);

}

Going via a solid seems to be clumsy and so I'd be interested in any comments!

Re: How to facet AcDbSubDMesh objects?

Anonymous — Wed, 02 May 2012 11:37:02 GMT

Adam

Thanks for that - very helpful - saw it just after I'd posted.

Can you offer anything on the smoothing/welding issue to reduce the face count for simple geometry?

Malcolm