[Gmsh] IDs of points forming a copy of entity (in python API)

[Marek Wojciechowski]

Dnia poniedziałek, 15 października 2018 18:04:13 CEST Christophe Geuzaine 
pisze:
> > On 15 Oct 2018, at 10:20, Marek Wojciechowski <mwojc at p.lodz.pl> wrote:
> > 
> > Hi!
> > 
> > I have a python script:
> > 
> > 
> > 
> > import gmsh
> > import math
> > 
> > model = gmsh.model
> > factory = model.occ
> > 
> > gmsh.initialize()
> > gmsh.option.setNumber("General.Terminal", 1)
> > 
> > model.add("spline")
> > 
> > factory.addPoint(0.2,-1.6,0,0.1, 101)
> > factory.addPoint(1.2,-1.6,0,0.1, 102)
> > factory.addPoint(1.2,-1.1,0,0.1, 103)
> > factory.addPoint(0.3,-1.1,0,0.1, 104)
> > factory.addPoint(0.7,-1,0,0.1, 105)
> > 
> > # periodic bspline through the control points
> > factory.addSpline([103,102,101,104,105,103], 100)
> > 
> > # COPY SPLINE HERE
> > dimTag = factory.copy([(1, 100)])
> > 
> > 
> > 
> > My question is how can i get a list of points forming copied spline?
> 
> That's not possible, as the copy of the spline will actually only create a
> single point. The initial points used to construct the first spline are
> actually not used in its topological description: only their coordinates
> are needed internally by OpenCASCADE. If you look at the copy by adding
> e.g.
> 
> factory.synchronize()
> gmsh.fltk.run()
> 
> at the end of your script, and if you select the new curve (101) in
> Tools->Visibility, you will see that it only depends on a single
> geometrical point (it is periodic). You can access that point with
> gmsh.model.getBoundary().
> 
> We could access, for each particular curve/surface type, the underlying
> parameters. In the case of a bspline like curve 101, we could access the
> poles, knots and multiplicities. Or for a circle, you could access the
> center. But there is no "general" way to access that data (unless we
> convert all curves to nurbs and give access to the parameters - which is
> probably not what you want).

Thank you very much for clarifications. getBoundary() semms to be what i was 
looking for. However for the closed spline, as in the example, getBoundary 
returns for me an empty list instead of a single point (gmsh-4.0.2). When the 
spline is open two points are returned as expected...


Regards,
-- 
Marek


 

--- 
Politechnika Łódzka 
Lodz University of Technology 

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