Hello,

I am using Gmsh v4.8.0. When I create a NURBS surface by calling the 
gmsh/model/occ/addBSplineSurface function in the Gmsh API, the function 
silently adds points and lines (presumably to create the boundary entities):

  1.  What is the recommended method to identify these silently added entities? 
Is it to call gmsh/model/occ/getEntities before and after calling 
addBSplineSurface to see what has been added?
  2.  Is it possible to replace these boundary entities (lines and points) so 
that I can get the topology correct?

After reading the comments in the makeTrimmedSurface() function, found in the 
Gmsh source code file GModelIO_OCC.cpp, I suspect (2) has been attempted in the 
past, but abandoned in preference for relying upon Geometry.Tolerance and 
Geometry.ToleranceBoolean to allow operations to succeed for topologically 
different yet geometrically identical (to within tolerance) entities. Is this 
correct?

My motivation for asking is I have been constructing geometry using the Gmsh 
API OpenCASCADE kernel functions, then synchronising, then calling 
gmsh/fltk/run to experiment with how I should control the Gmsh API. For some 
reason, the FLTK graphical user interface is not allowing me to successfully 
add a volume, which I have presumed to be due to incorrect topology (as my 
original approach for constructing a geometry resulted in lots of geometrically 
identical entities). As such, I have been put in effort to avoid geometrically 
identical entities to get the topology I want, but the addBSplineSurface is 
preventing me from being successful.

Many thanks,
Stephen

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