Hi Thomas, I understand the problems with changing topology by moving vertices.
But there are situations where no such topology changes can happen (wireframe of edges, triangular faces), and in other situation I would take care of updating the topology. All this depends on the simple question: how can I modify the coordinates of the vertices of a shape? I am discussing with these diagrams in mind : http://1.bp.blogspot.com/_ZnQO9nI8DrY/SYn-gThQeZI/AAAAAAAAAGs/C9FUDoDKdkY/s1600-h/abstract-1.png http://2.bp.blogspot.com/_ZnQO9nI8DrY/SYn-gi04zCI/AAAAAAAAAG0/ed5c_GHlW5g/s1600-h/abstract-2.png (It is the last two diagrams on http://opencascade.blogspot.com/2009/02/topology-and-geometry-in-open-cascade.html in case the picture links are broken) Each Compound, Face, Edge has a TopoDS_TShape list of subshapes. Iterating through them should lead me to the Vertex subshapes. Modifying their 3D_point should be reflected in the geometry of each element which is higher in the hierarchy of subshapes. Is it possible to iterate like this in pythonOCC? In OpenCascade? Is it the wrong track? Thank you Willy ________________________________ From: Thomas Paviot <tpav...@gmail.com> To: pythonOCC users mailing list. <pythonocc-users@gna.org> Sent: Thu, February 25, 2010 2:37:25 PM Subject: Re: [Pythonocc-users] retrieve vertices of an edge Willy, The use of hash codes in the Topology module *is* the essential difference. Regarding your sample at the end of the message, the result is not a surprise: the t.vertices() returns an iterator over the shape topology. When moving the vertex, you just move a copy of this vertex. But you also have to tell the TopoDS_Shape that it has to take the new coords into account. In your sample, when moving the vertex, you actually don't modify the shape, so the second time you iterate the vertices, you get the same results. I remember we already discussed that topic with Jelle: if one move a vertex, how could we update the underlying topology? This question is not simple, since when moving one vertex, you may modify the topology: for instance, if you move one vertex from a cylinder shape, the resulting shape is not a cylinder anymore. I know it is doable in the SpaceClaim CAD software: you load any topology (from a STEP file for instance), and then you just drag edges/vertices while the kernel ensures the shape consistency. Jelle started to implement something in this way: the Topology module provides a edges_from_vertex(self, vertex) method that returns edges connected to a vertex. But I don't know which algorithm should be performed over resulting edges. Best Regards, Thomas _______________________________________________ Pythonocc-users mailing list Pythonocc-users@gna.org https://mail.gna.org/listinfo/pythonocc-users
