[Gmsh] surface on a sphere

[Christophe Geuzaine]

Thomas.Bock at ptb.de wrote:
> Bonjour,
> 
> at first: sorry for the terrible long geo file ...
> 
> I like to have areas on the surface of a sphere. I decide to
> layout these areas as plane surfaces (see Plane Surface(221)).
> 
> Im _rather_ sure that all points of 221 are mathematically on the surface
> of the
> sphere, but gmsh seems to have an other opinion (221 does not fit to 223).
> 
> Can you give me a hint?

Hi Thomas - it's part of the legacy of our wonderful old interpolation
code ;-)

"Ruled surfaces" are actually interpolated using transfinite
interpolation--which cannot represent a sphere. As David said, there is
a hack in the interpolation code to check if all the bounding curves are
circle arcs with the same center... in which case we consider that the
patch is on a sphere.

I've just added another quick and dirty hack to always force a patch to
be spherical (see attached file): this will be available in tomorrow's
nightly snapshots.

PS: at the moment, for complex trimmed surfaces, you might be better off
using a "real" CAD system, export to STEP, then import the STEP back in
Gmsh to do the meshing.

> 
> BTW
> I'm am really happy that you still developing further gmsh!
> How about a u3d export function :) (ah! too many people
> bore you with long geo chunks ...):
> 
> Thanks in advance
> Thomas
> 

> 
> || Thomas Bock c/o Physikalisch-Technische Bundesanstalt
> || Abbestr. 2-12, D-10587 Berlin, Germany
> || Tel/Fax: ++49-30-3481-7354/7490, email: thomas.bock at ptb.de
> 
> 
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> 
> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine



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