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From: Toby Breckon <toby.breckon@cr...>  20090723 07:10:46

I am not aware of FronTier but using a higher order surface fit (e.g. parabola) should give better results  provided that locally the surface approximates a parabola well at every position over it's total area. This should be the case for the sphere but try it on something more complex  utah (openGL) teapot for example. Out of interest, Have you tried it with more nodes ? T. 2009/7/22 Márcio Ricardo Pivello <pivello@...>: > Hi, Toby, thanks for answering. > > I don't think low triangle count is the case here, since I'm working with > 20000 nodes. It seems to be a feature of the gaussian curvature algorithm, > since I got the same result for the same mesh using paraview curvature > filter. There is another package, FronTier > (http://www.ams.sunysb.edu/~linli/FronTier.html), which uses another way of > calculating the curvature, based on locally fitting a parabolic surface on > the region of interest, centered on the node in which the curvature is to be > calculated. Do you know anything about this lib or this methodology? > > best regards > > Márcio > > > On Wed, Jul 22, 2009 at 13:40, Toby Breckon <toby.breckon@...> > wrote: >> >> Increase the tessellation of the sphere (gts_surface_tessellate())  >> does the error go down ? >> >> Curvature is very noisy on highly subsampled surfaces, like a low >> triangle count sphere. This >> is possibly what you are seeing. >> >> Hope this helps, >> >> Toby. >> >>  >> Lecturer (Computer Vision & Image Processing) >> Applied Mathematics & Computing Group >> School of Engineering, Cranfield University >> Bedfordshire, MK43 0AL, UK. >> >>  e: toby.breckon@... >>  w: http://www.cranfield.ac.uk/~toby.breckon >> >> >> >> 2009/7/22 Márcio Ricardo Pivello <pivello@...>: >> > Hi. I've tried the functions from GTS and I found quite weird results >> > for a >> > unitradius sphere, with errors reaching 40% from the analytical value. >> > Is >> > there a remedy for this? >> > >> > >> > TIA >> > >> > >> > Márcio >> > >> >  >> > Márcio Ricardo Pivello >> > Universidade Federal de Uberlândia >> > Faculdade de Engenharia Mecânica >> > Laboratório de Mecânica dos Fluidos >> > (34) 3239 4040 ramal 618 >> > >> > >> > >> >  >> > >> > _______________________________________________ >> > Gtsgeneral mailing list >> > Gtsgeneral@... >> > https://lists.sourceforge.net/lists/listinfo/gtsgeneral >> > >> > >> >> >>  >> _______________________________________________ >> Gtsgeneral mailing list >> Gtsgeneral@... >> https://lists.sourceforge.net/lists/listinfo/gtsgeneral > > > >  > Márcio Ricardo Pivello > Universidade Federal de Uberlândia > Faculdade de Engenharia Mecânica > Laboratório de Mecânica dos Fluidos > (34) 3239 4040 ramal 618 > > 
From: Márcio Ricardo Pivello <pivello@gm...>  20090723 02:27:14

The front tracking method we work is based on an immersed boundary method, which uses normal and curvature information to calculate the forces that represent the interface. Sorry, but I'm quite new to this method, so I can't give deeper details right now... On Wed, Jul 22, 2009 at 18:49, Olumide <50295@...> wrote: > Márcio Ricardo Pivello wrote: > > I've never worked with thinplate splines specifically, just cubic > > splines, but it seems to be a very good choice. I'm worried about both > > computational cost and excessive smoothness of the interpolant, since > > the flow regime is very unstable: a high speed gas and a low speed > > liquid flowing inside a pipe (L=20D), the interaction between the phases > > leading drops to cross the interface in both directions. Therefore, > > accurate representation of the surface is necessary. > > Perhaps it would help if you explained why you need to compute the > curvature at points on the interphase. > > > >  > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral >  Márcio Ricardo Pivello Universidade Federal de Uberlândia Faculdade de Engenharia Mecânica Laboratório de Mecânica dos Fluidos (34) 3239 4040 ramal 618 
From: Olumide <50295@we...>  20090722 21:50:17

Márcio Ricardo Pivello wrote: > I've never worked with thinplate splines specifically, just cubic > splines, but it seems to be a very good choice. I'm worried about both > computational cost and excessive smoothness of the interpolant, since > the flow regime is very unstable: a high speed gas and a low speed > liquid flowing inside a pipe (L=20D), the interaction between the phases > leading drops to cross the interface in both directions. Therefore, > accurate representation of the surface is necessary. Perhaps it would help if you explained why you need to compute the curvature at points on the interphase. 
From: Márcio Ricardo Pivello <pivello@gm...>  20090722 20:39:26

I've never worked with thinplate splines specifically, just cubic splines, but it seems to be a very good choice. I'm worried about both computational cost and excessive smoothness of the interpolant, since the flow regime is very unstable: a high speed gas and a low speed liquid flowing inside a pipe (L=20D), the interaction between the phases leading drops to cross the interface in both directions. Therefore, accurate representation of the surface is necessary. thank you RT and Olumide. Best regards Márcio On Wed, Jul 22, 2009 at 16:07, Olumide <50295@...> wrote: > Ruhollah Tavakoli wrote: > > If you deal with multiphase flow, why do not use Gerris flow solver (on > > top of GTS) it use local elipsoidal fitting to estimate curvature. for > > details of gerris algorithm lok at recent paper by S. Popinet here: > > http://dx.doi.org/10.1016/j.jcp.2009.04.042 > > > > besides, you can smooth surface to improve results. there is an > > interative smoothing algorithm in GTS and also there is a feature > > preserving noniterative algorithm by TR Jones ... > > Unless your mesh/surface is noisy, I won't recommend smoothing. In fact, > this is the reason I didn't use the least squares fitting technique in > the paper I sent you (the fitted surface only approximates, but does not > pass though all the vertexes it is based on). > > What I did was to treat the 2ring set of vertexes about my point of > interest as a height field, and then fitted a 2d thinplate spline about > this set of vertexes. Just in case you didn't know, thinplate splines > are the smoothest possible interpolants. As such, I got really accurate > results. (I didn't originally did not go into all this detail because I > wasn't sure how much you know about thinplate splines.) > > However, if you want the best possible results, you can treat the entire > interphase between the two fluids as an implicit surface and fit a > variational implicit surface ( > http://graphics.cs.uiuc.edu/~jch/cs497jch/variationalis.pdf<http://graphics.cs.uiuc.edu/%7Ejch/cs497jch/variationalis.pdf>)on it. > > > >  > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral >  Márcio Ricardo Pivello Universidade Federal de Uberlândia Faculdade de Engenharia Mecânica Laboratório de Mecânica dos Fluidos (34) 3239 4040 ramal 618 
From: Olumide <50295@we...>  20090722 20:06:09

Ruhollah Tavakoli wrote: > If you deal with multiphase flow, why do not use Gerris flow solver (on > top of GTS) it use local elipsoidal fitting to estimate curvature. for > details of gerris algorithm lok at recent paper by S. Popinet here: > http://dx.doi.org/10.1016/j.jcp.2009.04.042 > > besides, you can smooth surface to improve results. there is an > interative smoothing algorithm in GTS and also there is a feature > preserving noniterative algorithm by TR Jones ... Unless your mesh/surface is noisy, I won't recommend smoothing. In fact, this is the reason I didn't use the least squares fitting technique in the paper I sent you (the fitted surface only approximates, but does not pass though all the vertexes it is based on). What I did was to treat the 2ring set of vertexes about my point of interest as a height field, and then fitted a 2d thinplate spline about this set of vertexes. Just in case you didn't know, thinplate splines are the smoothest possible interpolants. As such, I got really accurate results. (I didn't originally did not go into all this detail because I wasn't sure how much you know about thinplate splines.) However, if you want the best possible results, you can treat the entire interphase between the two fluids as an implicit surface and fit a variational implicit surface ( http://graphics.cs.uiuc.edu/~jch/cs497jch/variationalis.pdf )on it. 
From: Ruhollah Tavakoli <rohtav@gm...>  20090722 18:38:44

If you deal with multiphase flow, why do not use Gerris flow solver (on top of GTS) it use local elipsoidal fitting to estimate curvature. for details of gerris algorithm lok at recent paper by S. Popinet here: http://dx.doi.org/10.1016/j.jcp.2009.04.042 besides, you can smooth surface to improve results. there is an interative smoothing algorithm in GTS and also there is a feature preserving noniterative algorithm by TR Jones see this: http://people.csail.mit.edu/thouis/JDD03.pdf implementation of his algorithm by GTS is freely available (i have a copy) RT 2009/7/22 Márcio Ricardo Pivello <pivello@...> > Hi Olumide. > > I'm using gmsh (www.geuz.org/gmsh) to generate the mesh. In fact I need > accurate estimations for the curvature, since it will be used in a > multiphase flow solver to model the interface between different fluids. I've > heard of this surface fitting method, and I sure will write my version. > > > > Thanks a lot > > > Márcio > > > > On Wed, Jul 22, 2009 at 14:33, Olumide <50295@...> wrote: > >> > Hi. I've tried the functions from GTS and I found quite weird results >> > for a unitradius sphere, with errors reaching 40% from the analytical >> > value. Is there a remedy for this? >> >> Are you using the builtin (Gts generated) sphere? ... I suspect the >> method of curvature computation Gts uses is sensitive to the >> triangulation. >> >> I initially chose Gts because it computes curvatures and principal >> directions, however, I decided to write my curvature estimators. Its not >> too difficult. Just fit a(n analytical) surface about the vertex you're >> interested and the analyze the surface at the "point of interest" as >> described on page 5 ("Computing surface geometry") of the following >> paper: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.16.1571 >> >> >> >> >>  >> _______________________________________________ >> Gtsgeneral mailing list >> Gtsgeneral@... >> https://lists.sourceforge.net/lists/listinfo/gtsgeneral >> > > > >  > Márcio Ricardo Pivello > Universidade Federal de Uberlândia > Faculdade de Engenharia Mecânica > Laboratório de Mecânica dos Fluidos > (34) 3239 4040 ramal 618 > > > >  > > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral > > 
From: Márcio Ricardo Pivello <pivello@gm...>  20090722 17:58:53

Hi Olumide. I'm using gmsh (www.geuz.org/gmsh) to generate the mesh. In fact I need accurate estimations for the curvature, since it will be used in a multiphase flow solver to model the interface between different fluids. I've heard of this surface fitting method, and I sure will write my version. Thanks a lot Márcio On Wed, Jul 22, 2009 at 14:33, Olumide <50295@...> wrote: > > Hi. I've tried the functions from GTS and I found quite weird results > > for a unitradius sphere, with errors reaching 40% from the analytical > > value. Is there a remedy for this? > > Are you using the builtin (Gts generated) sphere? ... I suspect the > method of curvature computation Gts uses is sensitive to the triangulation. > > I initially chose Gts because it computes curvatures and principal > directions, however, I decided to write my curvature estimators. Its not > too difficult. Just fit a(n analytical) surface about the vertex you're > interested and the analyze the surface at the "point of interest" as > described on page 5 ("Computing surface geometry") of the following > paper: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.16.1571 > > > > >  > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral >  Márcio Ricardo Pivello Universidade Federal de Uberlândia Faculdade de Engenharia Mecânica Laboratório de Mecânica dos Fluidos (34) 3239 4040 ramal 618 
From: Olumide <50295@we...>  20090722 17:36:23

> Hi. I've tried the functions from GTS and I found quite weird results > for a unitradius sphere, with errors reaching 40% from the analytical > value. Is there a remedy for this? Are you using the builtin (Gts generated) sphere? ... I suspect the method of curvature computation Gts uses is sensitive to the triangulation. I initially chose Gts because it computes curvatures and principal directions, however, I decided to write my curvature estimators. Its not too difficult. Just fit a(n analytical) surface about the vertex you're interested and the analyze the surface at the "point of interest" as described on page 5 ("Computing surface geometry") of the following paper: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.16.1571 
From: Márcio Ricardo Pivello <pivello@gm...>  20090722 17:13:41

Hi, Toby, thanks for answering. I don't think low triangle count is the case here, since I'm working with 20000 nodes. It seems to be a feature of the gaussian curvature algorithm, since I got the same result for the same mesh using paraview curvature filter. There is another package, FronTier ( http://www.ams.sunysb.edu/~linli/FronTier.html), which uses another way of calculating the curvature, based on locally fitting a parabolic surface on the region of interest, centered on the node in which the curvature is to be calculated. Do you know anything about this lib or this methodology? best regards Márcio On Wed, Jul 22, 2009 at 13:40, Toby Breckon <toby.breckon@...>wrote: > Increase the tessellation of the sphere (gts_surface_tessellate())  > does the error go down ? > > Curvature is very noisy on highly subsampled surfaces, like a low > triangle count sphere. This > is possibly what you are seeing. > > Hope this helps, > > Toby. > >  > Lecturer (Computer Vision & Image Processing) > Applied Mathematics & Computing Group > School of Engineering, Cranfield University > Bedfordshire, MK43 0AL, UK. > >  e: toby.breckon@... >  w: http://www.cranfield.ac.uk/~toby.breckon<http://www.cranfield.ac.uk/%7Etoby.breckon>; > > > > 2009/7/22 Márcio Ricardo Pivello <pivello@...>: > > Hi. I've tried the functions from GTS and I found quite weird results for > a > > unitradius sphere, with errors reaching 40% from the analytical value. > Is > > there a remedy for this? > > > > > > TIA > > > > > > Márcio > > > >  > > Márcio Ricardo Pivello > > Universidade Federal de Uberlândia > > Faculdade de Engenharia Mecânica > > Laboratório de Mecânica dos Fluidos > > (34) 3239 4040 ramal 618 > > > > > > >  > > > > _______________________________________________ > > Gtsgeneral mailing list > > Gtsgeneral@... > > https://lists.sourceforge.net/lists/listinfo/gtsgeneral > > > > > > >  > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral >  Márcio Ricardo Pivello Universidade Federal de Uberlândia Faculdade de Engenharia Mecânica Laboratório de Mecânica dos Fluidos (34) 3239 4040 ramal 618 
From: Toby Breckon <toby.breckon@cr...>  20090722 16:40:31

Increase the tessellation of the sphere (gts_surface_tessellate())  does the error go down ? Curvature is very noisy on highly subsampled surfaces, like a low triangle count sphere. This is possibly what you are seeing. Hope this helps, Toby.  Lecturer (Computer Vision & Image Processing) Applied Mathematics & Computing Group School of Engineering, Cranfield University Bedfordshire, MK43 0AL, UK.  e: toby.breckon@...  w: http://www.cranfield.ac.uk/~toby.breckon 2009/7/22 Márcio Ricardo Pivello <pivello@...>: > Hi. I've tried the functions from GTS and I found quite weird results for a > unitradius sphere, with errors reaching 40% from the analytical value. Is > there a remedy for this? > > > TIA > > > Márcio > >  > Márcio Ricardo Pivello > Universidade Federal de Uberlândia > Faculdade de Engenharia Mecânica > Laboratório de Mecânica dos Fluidos > (34) 3239 4040 ramal 618 > > >  > > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral > > 
From: Márcio Ricardo Pivello <pivello@gm...>  20090722 14:02:14

Hi. I've tried the functions from GTS and I found quite weird results for a unitradius sphere, with errors reaching 40% from the analytical value. Is there a remedy for this? TIA Márcio  Márcio Ricardo Pivello Universidade Federal de Uberlândia Faculdade de Engenharia Mecânica Laboratório de Mecânica dos Fluidos (34) 3239 4040 ramal 618 
From: Paulo Henrique Junqueira Amorim <paulojamorim@gm...>  20090718 21:00:42

Hi Olumide, Thanks! More he read some other file format? Regards, Paulo 2009/7/18 Olumide <50295@...> > > I want to know if the GTS import and export STL format or vtkPolyData > > format? > > > > Is there any integration with VTK? > > > > Not found the information in the documentation. > > You haven't looked hard enough. GTS exports the VTK file format, but > does not read from it > > http://gts.sourceforge.net/reference/gtssurfaces.html#GTSSURFACEWRITEVTK > > You will therefore have to write your importer, but its very easy to do > so, if you know how to create a gts surface (take a look at the simplest > sample files). > >  Olumide > > > > > > > >  > Enter the BlackBerry Developer Challenge > This is your chance to win up to $100,000 in prizes! For a limited time, > vendors submitting new applications to BlackBerry App World(TM) will have > the opportunity to enter the BlackBerry Developer Challenge. See full prize > details at: http://p.sf.net/sfu/Challenge > _______________________________________________ > Gtsgeneral mailing list > Gtsgeneral@... > https://lists.sourceforge.net/lists/listinfo/gtsgeneral > 
From: Olumide <50295@we...>  20090718 20:53:16

> I want to know if the GTS import and export STL format or vtkPolyData > format? > > Is there any integration with VTK? > > Not found the information in the documentation. You haven't looked hard enough. GTS exports the VTK file format, but does not read from it http://gts.sourceforge.net/reference/gtssurfaces.html#GTSSURFACEWRITEVTK You will therefore have to write your importer, but its very easy to do so, if you know how to create a gts surface (take a look at the simplest sample files).  Olumide 
From: Paulo Henrique Junqueira Amorim <paulojamorim@gm...>  20090718 20:40:47

Hi All, Congratulations for the work! I want to know if the GTS import and export STL format or vtkPolyData format? Is there any integration with VTK? Not found the information in the documentation. Regards Paulo Amorim 