Hi Thomas,
thank you very much for the quick answer and for the simple solution.
(I studied the Topo._loop_topo() method, and I can't see why their use of
TopExp_Explorer succeeds while mine fails. I don't see an essential difference
except they use hash codes to get unique result sets.
Strangely, in my example code after the first call v[0]=ex.Current(), v[0] is
not Null. But after ex.Next() and v[1]=ex.Current(), both v[0]==v[1] and
v0.IsNull() is True. Whatsoever, the Topology package solved this problem)
Next I want to implement possibilities to clean data stored in a large
wireframe of Edges, or in a Compound of Faces.
I need to relocate single vertices so that the Edges follow the movement of the
vertices. (A more complicated case would involve to relocate edges or faces of
a compound so that neighbouring elements follow the movement without changing
the topology. Of course this is not always possible, so lets discuss the simple
movement of edges connected to one vertex in a wireframe.)
I cannot use a mesh structure, because it does not preserve the topology of
solids, faces and edges which make our parts.
Making use of your Topology.Topo class I have modified my previous example. I
get the coordinates of the two vertices correctly, translate them, and get them
a second time from the original edge. Unfortunately they are the same before
and after the translation:
before:
(0.0, 0.0, 0.0)
(0.0, 0.0, 1.0)
after:
(0.0, 0.0, 0.0)
(0.0, 0.0, 1.0)
Apparently the translation only operates on a copy of the edge vertices, so
that the edge itself is not modified.
I know this has been discussed before, and the only solution I have found is to
delete the edge and create a new edge with the modified vertices. But this is
infeasible if you are working on a large structure, where the edges and faces
may be connected to hundreds of other elements.
Has someone recently found a method to modify the vertices used by the Shape
structure? I can't imagine this is such a difficult problem, or is the reason
the way how smart pointers are handled in pythonOCC/Swig? Is it easier to
translate vertices using OpenCascade directly instead of pythonOCC?
I attach the new code snippet and hope you have another simple explanation.
Did I mention how much I appreciate this project and the support on this list?
It is outstanding :)
Willy
from OCC.BRepBuilderAPI import *
from OCC.TopoDS import *
from OCC.TopAbs import *
from OCC.TopExp import *
from OCC.TopLoc import *
from OCC.gp import *
from OCC import BRep
from OCC.Utils.Topology import Topo
e=BRepBuilderAPI_MakeEdge(gp_Pnt(0,0,0),gp_Pnt(0,0,1)).Edge();
t = Topo(e)
trsf=gp_Trsf()
trsf.SetTranslation(gp_Vec(0,0,-1))
bt=BRep.BRep_Tool()
print "before:"
for vertex in t.vertices():
print bt.Pnt(vertex).Coord()
vertex.Move(TopLoc_Location(trsf)) #translating every vertex, as example
print "after:"
for vertex in t.vertices():
print bt.Pnt(vertex).Coord()
#why are these the same as before??
________________________________
From: Thomas Paviot <tpav...@gmail.com>
To: pythonOCC users mailing list. <pythonocc-users@gna.org>
Sent: Thu, February 25, 2010 12:46:54 PM
Subject: Re: [Pythonocc-users] retrieve vertices of an edge
2010/2/25 Thomas Paviot <tpav...@gmail.com>
2010/2/25 Willy Hertz <willy.he...@yahoo.com>
>
>
>>>
>>The conversion between TopoDS_Shapes, Vertices and Coordinates is driving me
>>crazy.
>>My goal is to find the vertex coordinates of any displayed object. I found a
>>few similar questions here and in the opencascade forums, but the replies
>>seem not to work with pythonOCC. I am trying the following procedure:
>>>>
>>1) extract all vertices with TopExp_Explorer
>>2) convert each TopoDS_Shape into a Vertex
>>3) get the coordinates using OCC.BRep.Brep_Tool.Pnt(vertex) ... not discussed
>>in this post
>>
>>Please have a look at the following code, which creates an Edge and attempts
>>to extract the vertices.
>>>>
>>Unfortunately in step 1) three shapes with ShapeType=Vertex are returned, the
>>first two being identical and pointing to Null. Why?
>>
>
>
>Hi Willy,
>
>
>This point has already been discussed on this ml (I don't have the reference
>to the discussion, will find it).
>
>
>Jelle implemented a topology traversing algorithm on top of the built-in
>TopExp_Explorer class. I sugest you use it. It can be done very simply:
>
>
>from OCC.Topology import topo
>t = Topo(my_TopoDS_Shape)
>
>
>Then you can iterate to ver shapes, vertices, edges etc:
>
>
>for vertex in t.vertices():
> ...do_whatever_you_want
>
>
>Have a look at the source code of the Topo class
>(http://code.google.com/p/pythonocc/source/browse/trunk/src/addons/Utils/Topology.py)
> and/or the documentation (http://www.pythonocc.org/APIREF/index.html).
>
>
>Best Regards,
>
>
>Thomas
>
>In step 2) the method TopoDS.Vertex(vs[2]), applied to the
>> third shape vs[2] complains about "<type 'exceptions.RuntimeError'>:
>> Standard_TypeMismatch".
>>
>>How do I retrieve the Vertex coordinates of an Edge or (later) any other
>>Shape?
>>
>>Regards,
>>>>
>>Willy
>>
>>The code example:
>>from OCC.BRepBuilderAPI import *
>>from OCC.TopoDS import *
>>from OCC.TopAbs import *
>>from OCC.TopExp import *
>>from OCC.gp import *
>>
>>e=BRepBuilderAPI_MakeEdge(gp_Pnt(0,0,0),gp_Pnt(0,0,1)).Edge();
>>>>
>>exp=TopExp_Explorer()
>>exp.Init(e,TopAbs_VERTEX)
>>vs=[exp.Current()]
>>exp.Next()
>>vs=vs+[exp.Current()]
>>exp.Next()
>>vs=vs+[exp.Current()] #strangely 3 vertices are found
>>
>>print 'identical:'
>>>>print vs[0]==vs[1] #True
>>>>print vs[1]==vs[2] #False
>>print 'IsNull:'
>>print vs[0].IsNull() #True
>>print vs[1].IsNull() #True
>>print vs[2].IsNull() #False
>>
>>tds=TopoDS()
>>vx=tds.Vertex(vs[2]) #ERROR: <type 'exceptions.RuntimeError'>:
>>Standard_TypeMismatch
>>>>
>>print vx
>>
>>
>>
My previous message was not very clear. Here is a small sample to illustrate
it: a box is created, all vertices are then obtained from the Topo class (8
vertices) and converted to a gp_Pnt. Finally, the X,Y an Z coordinates are
displayed:
############## Python Code ##################
from OCC.BRepPrimAPI import *
from OCC.Utils.Topology import *
from OCC.BRep import *
# Create shape
my_shape = BRepPrimAPI_MakeBox(10,20,30).Shape()
# Traverse topology
t = Topo(my_shape)
for vertex in t.vertices():
pnt = BRep_Tool().Pnt(vertex)
print 'X',pnt.X(),'Y',pnt.Y(),'Z',pnt.Z()
############# End of python code ################
And here is the ouput:
X 0.0 Y 0.0 Z 30.0
X 0.0 Y 0.0 Z 0.0
X 0.0 Y 20.0 Z 30.0
X 0.0 Y 20.0 Z 0.0
X 10.0 Y 0.0 Z 30.0
X 10.0 Y 0.0 Z 0.0
X 10.0 Y 20.0 Z 30.0
X 10.0 Y 20.0 Z 0.0
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