# STEP/STL model traversal vertices question

Firstly, the rectangular model is used as the standard to explain, and the number of vertices is 8.

Next, I read the model and use the code to traverse the number of vertices of the model:

``````for (aVertexExp.Init(shape, TopAbs_VERTEX, TopAbs_SHAPE); aVertexExp.More(); aVertexExp.Next()) {
vertexCount++;
}``````

The number of vertices obtained here is 48;

Finally I use other methods to get vertices:

``````TopLoc_Location aLocation;
Handle(Poly_Triangulation) myT = BRep_Tool::Triangulation(myFace, aLocation);
TColgp_Array1OfPnt nodes(1, myT->NbNodes());
for (int i = 0; i < nodes.Length(); i++) {
gp_Trsf edgeTransf = aLocation.Transformation();
gp_Pnt aPoint = nodes.Value(i + 1);
// cout << "Point info -> " << aPoint.X() << "," << aPoint.Y() << "," << aPoint.Z() << endl;
gp_Pnt p = aPoint.Transformed(edgeTransf);
// cout << "Point info -> " << aPoint.X() << "," << aPoint.Y() << "," << aPoint.Z() << endl;
// cout << "Point info -> " << p.X() << "," << p.Y() << "," << p.Z() << endl;

this_face.vertex_coord.push_back(p.X());
this_face.vertex_coord.push_back(p.Y());
this_face.vertex_coord.push_back(p.Z());
}``````

The number of vertices obtained by this method is 24.

Because a vertex will be shared by all three edges, it is three times the number of vertices after meshing.

I can use this method to filter out duplicate vertices and get non-redundant vertices.

However, I can't understand why the first method is 6 times the number of vertices.Hope someone can answer the question.

thanks agin.

Sunlin. Hello. TopoDS_Vertex not related with nodes.

TopoDS_Vertex related to the Edges of the face. Pnts that you extract from mesh just a nodes.

Best regards, Dmitrii. Could you explain in detail how TopoDS_Vertex related to the Edges of the face? Or is there any relevant documentation that can be provided?

If I want to obtain the number of vertices of the real model through OCCT, which data should I obtain?

Best regards, Sunlin. They are not related at all.

TopoDS_Vertex a topology component. It can be free vertex or begin or end of the TopoDS_Edge (topology component).

Poly_Triangulation is a mesh structure. nodes in this structure a vertices is triangle vertices.

Best regards, Dmitrii. Is there a way to get the real-world coordinates of a TopoDS_Vertex? Or a TopoDS_Edge? TopoDS_Vertex is just an gp_Pnt. TopoDS_Edge can contains any types of curves.

To extract geometry from topology, you can use:BRep_Tool

Best regards, Dmitrii.