Hi Akos, > as one of the original implementors of the NURBS support, I > feel I should > clarify some of our design decisions. :-)
Thanks. It's always good to hear from the real experts :-) > We abandoned the sewing approach mainly because no matter > what methods we > tried (and we tried some) it never worked well for all > models. Usually it > handled some models quite well and didn't work at all for > other models. I > know some people dislike the Fat Borders approach, but it > works reasonably > well for rendering. It's also used in our GPU NURBS framework > which seems > to be quite popular, despite not even having an explicit mesh. :-) I could not find any documentation for this. Can you please point me to something that I can take a look at and play with? Is this part of the CVS tree? The only thing I could find on google was this 2002 paper from U Bonn which talks about the Sewing algorithm in OpenSG Plus. Nothing about Fat Borders or the GPU NURBS stuff. > As for collision detection, I think it's actually possible to use the > OpenSG generated meshes even though they're not crackfree, > because you > still get guaranteed geometric precision in model space (which is not > trivial to achieve). That is good to hear. > AFAIK topological reconstruction of arbitrary NURBS models is > still an > open question. I'm not an Optimizer expert by any means so > feel free to > correct me here but I don't think Optimizer's one pass/two pass > reconstruction methods work that well in bad cases (e.g. non-manifold > topology). Actually the description of their two pass method > sounds rather > similar to our seam-graph approach, which I know didn't work > in all cases > (and we spent a _lot_ of effort on that one). > > Also AFAICS Optimizer more or less tessellates into a grid > which may or > may not be what you want, plus I really don't think it > guarantees you a > completely gapfree mesh (even inside one topology). > > Anyway, if you want to tackle writing your own sewing-method, > the best > approach would probably be writing some kind of > "sewing-Action". However, > even if you have some kind of topological information this is > far from > trivial, consider e.g. two adjacent surfaces which are both > trimmed on the > joint side with differently parameterized curves: you're > basically out of > luck... (and this is not an uncommon scenario in industrial > models that > I've seen so far.) Thanks a lot for your inputs. I guess, I will try what is available today in OpenSG and then see if that is 'good enough' for our application/data sets or if we need to improve on that. If it turns out to be the later, I will make sure that I discuss with the rest of the folks on the list before diving into it directly. - Praveen Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Opensg-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/opensg-users
