How to facet AcDbSubDMesh objects?

[Anonymous]

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

[Alexander.Rivilis]

What about using method explode of class AcDbSubDMesh?

[adam.nagy]

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

[Anonymous]

Ah

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!

[Anonymous]

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