[Gmsh] "Tag # already exists" with OpenCASCADE engine

[Christophe Geuzaine]

> On 17 Oct 2018, at 23:25, Wang Bin <binwang.0213 at gmail.com> wrote:
> 
> Dear Dr. Geuzaine,
> 
> Thanks for you rapid reply. 
> 
> Based on your suggestion, now I'm working on normal vector issue in a simplified problem.
> 
> Now I found a potential bug in Gmsh. When I use build-in geometry engine, the normal vector are all in the same direction.
> But when I switch to OpenCASCADE engine (adding SetFactory("OpenCASCADE")), the normal vector shows different. All of other info in geo file is exactly the same. 
> 
> How do I resolve this issue?

It's a limitation of the current OpenCASCADE interface: signs in curve loops are ignored - they just don't have any effect.

Curve Loop(cl4) = {-l8,l7,l9};

should thus be written

Curve Loop(cl4) = {l7,l9,l8};

if you want the orientation to be governed by l7.


> <image.png>  <image.png>
> 
> Please check attachment geo file to see the details.
> 
> Thanks,
> Bin
> 
> Christophe Geuzaine <cgeuzaine at uliege.be> 于2018年10月16日周二 下午4:39写道：
> 
> 
>> On 16 Oct 2018, at 17:03, Wang Bin <binwang.0213 at gmail.com> wrote:
>> 
>> Dear Developers,
>> 
>> Thanks for the nice mesh generator.  Now I'm trying to use BooleanFragments in OpenCASCADE engine to mesh some "compsolid" model (picture) with conforming mesh on the common interface (see attachment geo file). 
>> 
>> <compsolid.PNG>
>> But the OpenCASCADE engine will add new Points, Lines or Surfaces during the boolean operation. Thus, Gmsh keeps give me a error "Point/Line/Surface # already exists".
>> 
>> So, is there any method/tricks to avoid this issue? Such as reserve some tag id for the New geometry objects. Why Gmsh not using "newreg" internally to append new geometry?
> 
> Your surfaces are not correctly oriented, which leads to the creation of new entities when you create "surface loops". The duplicates are reported when you force the creation of new points after these extra entities have been created.
> 
> Christophe 
> 
> 
> 
> 
> 
>> 
>> Thanks for your help!
>> -- 
>> Bin Wang  
>> PhD Student
>> Craft & Hawkins Department of Petroleum Engineering
>> Louisiana State University
>> 2245 Patrick F Taylor Hall, Baton Rouge, LA  70803
>> <composolid_new.geo>_______________________________________________
>> gmsh mailing list
>> gmsh at onelab.info
>> http://onelab.info/mailman/listinfo/gmsh
> 
> — 
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science 
> http://www.montefiore.ulg.ac.be/~geuzaine
> 
> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
> 
> 
> 
> -- 
> Bin Wang  
> PhD Student
> Craft & Hawkins Department of Petroleum Engineering
> Louisiana State University
> 2245 Patrick F Taylor Hall, Baton Rouge, LA  70803
> <ori.png><face6_buildin.geo><face6_OpenCASCADE.geo><ori.png>

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

Free software: http://gmsh.info | http://getdp.info | http://onelab.info