Yes, this will solve the problem provided I have tetrahedral elements available for given Triangle. I wanted to know if GMSH provides some way to get outward normal without me finding its corresponding volume element. I haven't found anything like that in their code till now. I should better use method given by you.
Thanks a bunch, Ashish From: Ashish Garg [mailto:[email protected]] Sent: Thursday, May 03, 2012 1:59 PM To: Mark Starnes Cc: Negi, Ashish; [email protected] Subject: Re: [Gmsh] outward normal of surface triangles Hello Ashish, Ya got your problem. See you know all tetrahedra at the boundary surfaces. It means u know all the vertex of the tetrahedra ( out of four vertex three r makin boundary faces right ) . try this v0 = face[i].vertex[0]; v1 = face[i].vertex[1]; v2 = face[i].vertex[2]; r01 = vertex[v1] - vertex[v0]; r12 = vertex[v2] - vertex[v1]; face[i].normal = (r01 X r12); // Check orientation of normal fourth_vertex = face[i].vertex[3] check_normal_orientation = face[i].normal * ( fourth_vertex- vertex[v0]); if ( check_normal_orientation > 0.0 ) face[i].normal *= -1.0 ; this will resolve your problem for sure. regards Ashish Garg TIFR-CAM, Bangalore On Thu, May 3, 2012 at 1:22 PM, Mark Starnes <[email protected]<mailto:[email protected]>> wrote: Hi Ashish, Does it help if you change the sign of every line entry number in the Plane Surface definition that is a problem? Best regards, Mark. On Thu, May 03, 2012 at 06:23:34AM +0000, Negi, Ashish wrote: > Hi Ashish, > > > > Thanks for replying. > > > > Let me explain my problem again. I have attached 3 pictures below. First, > shows > a Tetrahedral mesh of square duct. So, all surface elements are Triangle. > Second, shows normal vectors computed using cross product if Triangle vertices > are saved in clockwise sense (in the picture). Third, shows normal vector > computed if Triangle vertices are saved in anti-clockwise sense. So, second > picture gives me outward normal which I need. > > > > I found that all Triangles do not give me outward normals if I assume > clockwise > sense (in following picture). So, I wanted to know if GMSH has some other way > to provide me outward normal for each surface Triangle. > > [cid] [cid] > > > > Thanks, > > Ashish > > > > From: Ashish Garg > [mailto:[email protected]<mailto:[email protected]>] > Sent: Wednesday, May 02, 2012 1:09 PM > To: Negi, Ashish > Cc: [email protected]<mailto:[email protected]> > Subject: Re: [Gmsh] outward normal of surface triangles > > > > Hi Ashish > > give the condition that the cross product should be greater than zero. I guess > it will resolve the problem. > > Ashish Garg > > On Wed, May 2, 2012 at 12:38 PM, Negi, Ashish > <[email protected]<mailto:[email protected]>> > wrote: > > Hello Everyone, > > > > I?ve been using GMSH library to open Nastran BDF file and extract mesh data > for > my software. I generally load a mesh consisting of only Tetrahedra. Hence, > surface of model have only Triangle elements. > > > > I want to find outward normal at each Triangle. I get coordinates of each > Triangle and then take cross product to get normal to the element. But, I?m > not > sure if it will always be outward. Can someone suggest a solution to this > problem? > > > > Thanks, > > Ashish > > > > > > > _______________________________________________ > gmsh mailing list > [email protected]<mailto:[email protected]> > http://www.geuz.org/mailman/listinfo/gmsh > > > > _______________________________________________ > gmsh mailing list > [email protected]<mailto:[email protected]> > http://www.geuz.org/mailman/listinfo/gmsh -- Dr. Mark Starnes Principal Physicist FT Technologies Church Lane Teddington TW11 8PA web: www.fttech.co.uk<http://www.fttech.co.uk> DDI: 0208 614 2730
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