Hello,

Despite having Spaceclaim I'm not sure about G2/G3 fillets. I use VSR for Rhino for surfacing tasks and v3 out next month has filleting added. VSR just got bought up a few weeks ago by Autodesk and they've said they'll continue Rhino support but who knows if this will turn into another TSplines situation. After seeing a demo of the fillet functionality it's worth the price for that addition in my opinion.

Hello,

As BurrMan suggested perhaps providing an example problem can help you make a choice.

""""""Despite having Spaceclaim I'm not sure about G2/G3 fillets."""""""""

Also, I think you'll find it hard to dig up any packages that actually do this. Maybe a basic tick for G2, with no options, but G3? The higher end ones will start to use surface blends to work in higher continuity. So they'll have you do a fillet, then delete and replace it with surface blends. The geometry library Michael uses is one supplier that does offer it. You can find it in 3dmax also.... Looks like luxology has been hooking up with them too....

Sorry for the late reply, this forum somehow doesn't notify me of replies, although I'm subscribed to the thread.

Thanks for all the feedback!

- Elliptical Fillets are basically the same when it comes to tangency as circular ones, just with two different radii IMO? Or am I off the mark here?

- Well, if Catia is that expensive, maybe it does good fillets ;-)

- I'm sorry but I can't post anything, it's under NDA.

- I'll not go near anything Autodesk if I can avoid it.

- While I have a modo 601 license, I'm not too hot about that company/software either. ;-)

But the idea to delete the circular blend and then replace it with a surface blend could be at least interesting to try. I guess it would end up being a lot of work, especially at the corners.

Well, I'll see what my customer can do in Catia and if all else fails, I'll do it in polygons with Subdivision Surfaces before I get lost in too complex a NURBS setup.
This would have some other benefits as well like a more even mesh and easier UV-Mapping.

Edit: Just checked on Spaceclaim and VSR, but that is all outside of the margin of this job pricewise.

Thanks again!

Tom

Well, I guess I wonder what poly/subD program you are looking at that does "G3"? I mean, max has some (your dreaded autodesk)...

The subd will make nice, mushy smooth surfaces, but you were specifically speaking about G3?

Anyway.....

Every good Catmull Clark Subdivision Surface implementation with Edge Weighting gives you perfect visual continuity in reflections.
The mushyness is countered by the edge-weighting.
You have other problems with SDS that are easier to solve with NURBS, but for relatively organic forms it's perfect.

For example:
http://www.screendream.de/Site/3d-design/sculpture.html#/3

That is from Softimage XSI, which has one of the best implementations I've seen. After Autodesk bought them, I ended my subscription when it became clear that it is no longer going anywhere, but I still have a license. Now I work more in Lightwave 3D again, where the SDS and especially the edge-handling aren't as good, but still you can get similar results, although with a bit more fiddling.

Since I come from the polygon-world originally, I'm always amazed how much effort and money are needed to get something similar in NURBS. ;-)

Cheers,

Tom

EDIT: Just to be clear: what I am looking for is visual continuity in reflections. The discussions aren't always clear if G2 or G3 is needed for that.
Sorry for any confusion that may have caused.

Hi Tom, you only need G2 for there to be visual continuity with reflections, G3 is more for bragging rights than anything you can actually see on the geometry.

- Michael

hehehe - okay, I take your word for it.

I usually use G3 in MoI when it works since I like the created profile - looks more natural or organic to me, similar to what SDS create, a certain kind of flow. Most of the time NURBS look too dead to me.

Cheers,

Tom

Hi Tom, yeah if you're trying to make organic looking forms, usually sub-d modeling is a better fit for that style of stuff than NURBS modeling.

NURBS modeling is good for shapes that are well defined by 2D profile curves.

- Michael

""""""""""Every good Catmull Clark Subdivision Surface implementation with Edge Weighting gives you perfect visual continuity in reflections.
The mushyness is countered by the edge-weighting. """"""""""

Catmull clark is "trying" to give you C2, though it can still result in C1 at extraordinary vertices. It does this by melting everything down to try that average. Repeated subs can get close. The "perfect VISUAL curvature" result just means you "cant see the difference".

I was thrown by the request being "G3", or even "G2". There's is a difference.

"""""""""Since I come from the polygon-world originally, I'm always amazed how much effort and money are needed to get something similar in NURBS"""""""""

That's because the NURBS are actually perfect, and "DO" represent that. It's much easier to kindof "average everything down" to be somewhat close........

But like Michael points out, YOU cant really see the difference.

But there is a need in very specialized situations, where those values cant just be "moved around"........

Well, since it seems that there's no G2 Fillets in any affordable software either, it's moot anyway. ;-)

And I have little influence on what my customers choose to do their work in. ;-)

Let's leave it at that.

Cheers,

Tom

"""""""""Well, since it seems that there's no G2 Fillets in any affordable software either, it's moot anyway. """"""""""""""

Well, MoI does G2 fillets. Also G3 fillets as well.

""""""""""It's really too bad that on these models, imported from Catia as Step, I can't even fillet a single trivial edge, no matter what mode in MoI."""""""

But why?

Can you produce "ANY" example that doesn't work, that is not under NDA? I mean, a "single trivial edge" is kindof a broad, general statement.

Burr, let it rest, it's okay.

Wow. Ok Tom.

Darn! I wanted to see these 'unfilletable' edges too, oh well I guess we'll just stick with edges that do fillet.

-

Just to add some follow up on this:
Catia is unable to fillet those models as well, neither me nor my customer really understand why, but before we dive into endless debugging sessions, we decided that I'll rebuild the models for now as SDS objects - and he will look into MoI/Rhino for future construction. :-)

I only need the fillets for visualisation and rendering, so the results from SDS are just fine, therefore I didn't want to go into a loop discussion ;-)
Sorry if I came over defensive.

Thank you all very much for the input!

Cheers,

Tom