[Gmsh] surface normal orientation - geo vs. mesh

[David Colignon]

Hi,

from :  http://www.geuz.org/pipermail/gmsh/2002/000581.html  :

You can choose the orientation by setting a + or - sign in
the definition of the Physical Surface. (Check the result by _reloading_
your mesh, and setting a nonzero value for the "Normals" option in
Options->Mesh->Visibility).

See also 

http://www.geuz.org/pipermail/gmsh/2003/000744.html

http://www.geuz.org/pipermail/gmsh/2003/000918.html

http://www.geuz.org/pipermail/gmsh/2002/000638.html



David Colignon



> ----------------------------------------
> From: Philip Kelleners <P.H.Kelleners at ctw.utwente.nl>
> Sent: Tue Jun 28 15:01:44 CEST 2005
> To: <gmsh at geuz.org>
> Subject: [Gmsh] surface normal orientation - geo vs. mesh
> 
> 
> Dear Christophe,
> 
>   first my compliments, for producing such quality software and for releasing
> the sources under GPL. It compiles nicely under Irix 6.5 using the native mips
> compiler and even runs at decent speed on an older SGI-O2.
> 
>   I may have hit upon a bug, if not, I don't understand the result. The
> following lines are part of a bigger .geo file but mesh by themselves.
> 
> 
> 
> ***** begin  normal-ori.geo *****
> 
> // In gmsh 1.60.1;
> // the surface normal of the geometry, points in the opposite direction
> // of the surface normals of the mesh
> 
> dn = 0.6;
> dz = 100;
> 
> rcc = .1;
> rcb = .5*(94.6 - 89.3);
> rca = .5*(rcc*rcc + rcb*rcb)/rcc;
> 
> Point(1405) = { 89.30, 19.60,  0.00, dn};	// start tip
> Point(1406) = { 92.00, 19.60,  0.10 - rca, dz};	// Center of top circle
> Point(1407) = { 94.60, 19.60,  0.00, dn};	// end tip
> 
> Line(1404) = {1405, 1407};
> Circle(1405) = {1405, 1406, 1407};
> 
> Line Loop(1404) = {1405, -1404};
> Plane Surface(1404) = {1404};
> 
> ***** end   normal-ori.geo *****
> 
> 
> 
> ***** output of gmsh -info *****
> 
> Version        : 1.60.1
> GUI toolkit    : FLTK 1.1.6
> License        : GNU General Public License
> Build OS       : IRIX64 6.5
> Build options  : GSL TRIANGLE NETGEN JPEG PNG ZLIB MATHEVAL 
> Build date     : Wed Mar 30 00:28:26 MEST 2005
> Build host     : removed
> Packager       : philip
> Web site       : http://www.geuz.org/gmsh/
> Mailing list   : gmsh at geuz.org
> 
> ***** output of gmsh -info *****
> 
> 
> 
>   In the main-graphics window of GMSH, the surface-normal of the geometry,
> points downwards in negative y-direction, whereas the surface-normals of the
> triangle-mesh point in the opposite direction. On other surfaces I mesh, the
> normal directions of the geometry and the mesh are consistent. Can the strange
> behaviour in the case be related to the small curvature of the circle?
> 
>   other points/questions:
>   
> -  I like to point out that when using the gui-options or gui-visibility menu's
> I am troubled by the need to press 'apply' every time I change settings. Is
> there a way to switch off this behaviour (in GMSH or FLTK) and make changes
> come into effect the moment you've clicked on them? Otherwise I would welcome
> such a possibility in future releases.
> 
> -  Memory use of the 3D netgen algorithm seems so much larger compaired to the
> isotropic algorithm. To the point of netgen exceeding the 2gb barrier
> (resulting in an abort of the program) for a geometry which when meshed
> isotropic, results in 24957 nodes and 139848 elements. Does this comaire with
> your experience?
> 
> -  Is it correct for GMSH to output meshes, containing nodes which are not
> referenced by any of the elements in the mesh?
> 
> 
> Regards, Philip
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh

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