Hi @digiformer thank you for your feedback.
When I make like a sweep2 with say, 3 sweep2 coming together for multiblends, I can’t get a good continuity on the surfaces. Like a letter K but a curvy in all axis
Is it that I need to start with curve more than degree3？
Or degree does not matter and I need crosssections of the sweep2 to have three edge points to allign on a line?
There is no insufficient quality in that model that’s just your biased opinion. The model has G1 seams, but if those seams were on a manufactured part nobody would be able to see where the seams are located. I base that opinion on many years of experience creating lots of models with seams like that have been manufactured. What do you base your opinion on?
How do you know that there is a G1 seam there?. That could just as easily be one continuous surface (there’s no seam there at all)
Yeah there’s no abrupt “G1” transition there. Is that a phone? Those things are brute-force point-sculpted beyond all reason, they’re not going to be examples of “ignoring” anything.
If those who have to resort to juvenile language work for uncaring clients in uncaring industries, G1 is perfectly ok. To dismiss that there is a wealth of quality conscious clients from FMCG, medical, sports equipment and electric goods sectors, let alone aircraft, marine and public transportation sectors, is nothing but absurd.
I think these kinks are caused by the tessellation of the model is too low. Turn on the preview of render polygons and i believe you will find polygone edges right at the kinks.
Evaluation tools using shaded or rendered views will never tell you the whole truth. How close you get to the truth depends from the fineness of the polygon mesh the tool is forced to use.
To avoid misunderstandings: Zebra and friends are of course a very good method for assessing the visual quality of the model.
Go to the custom polygon settings of your model, put every value to zero and play around with the “maximum angle” value. Go below 0.5. But be careful. This is quite resource demanding. You have to try out what your system can handle.
Uhh, you guys ar
Uh, you guys are new here, right? Accusing lowercase jim of being lazy or ‘uncaring’? Hah, oh, wow. No, he’s more obsessed with the quality of Rhino geometry than probably anyone
Hmm I think I need Help in learning creating curvature continuous surfaces.
For example, I’d like to make three way surface coming together and connect with surface continuous segments.
I was thinking extracting Isocurve, then blendcrv(getting the curve in blue)
then sweep2 to get the surface.
But, looks like it’s not working so well.
Is it the cross sections I need to go back to?
Is it the degree 3 curves which are not suitable?
Any tutorial/links etc… is appreciated.
I’d like to learn from scratch of setting up good curves -> making good surfaces -> making good polysurface.
Curvature Continuous.3dm (319.6 KB)
It’s the footplate of my DELL display. Maybe some of you have something similar in front of you. You can check it out right away.
It is of course true that my assertion would only be proven if the design data for the injection mold could be checked.
But actually, every time I had G1 data built in real, I got this results. My G2 transitions dont do that :).
If this were mathematically curvature continuous, it would be poorly done. Of course, this is also possible. It could even be the will of the designer. In my experience, modellers who are familiar with CC and designers would want to avoid such a result.
nobody would be able to see where the seams are located
hmm what material? I can not believe that.
What do you base your opinion on?
I had this discussion years ago in my work. There were people who, for example, loved Apple products because of their design, but at the same time claimed that Curvature Continuity was bad design. It would make the body soapy and imprecise. So they were even more radical than you 
.
They got really angry when I claimed that Apple would surely build G2 or more. It’s true, that’s just a hunch of mine.
I could convince them to build some models (Fridge Bins) twice. One with G1 fillets and one with G2 fillets.
Believe me, I’ve worked on the G1 data with the same attention to detail as on the G2 data. I really wanted to find out for myself what the difference is in the end.
To me G2 is only the higher level of continuity (mathematically G1=first derivation, G2=second derivation - you might remember school). That doesn’t really change the design. But it makes the sculpture more pleasing to the viewer and perhaps also to the touch.
The result was convincing for Curvature Continuity. The parts were then constructed as usual with G1, but the construction department began to move.
Actually, every time I had G1 data built in real, I got the results you can see at the screen footplate.
Isnt it exactly what the evaluation tools show at G1 seams? Hard breaks in the reflected contours. And the same phenomenon appears when you shade or render this models. So until now this was enough proof to me.
Please remember that i pointed out my opinion from the point blank of view of designers and shapers.
I understood the “marketing bs” comment as an statement of absolute validity, that there would be no recognizable difference between G1 and G2 transitions . And i felt like the model you provided should proof that. I looked at it and the surface seams immediately jumped into my eyes ;). I just wanted to point that out. Thank you very much for staying calm on that, Jim.
Industrial design is certainly more than just finding beautiful shapes. That’s why I added that there are situations where you have to be content with G1. But so far I have not been able to find any design reasons.
phuu that was a lot of text…sry
Is it the degree 3 curves which are not suitable?
I am not so good in the use of Rhino terms.
I hope I can spell that in an understandable way…
G2 continuity requires that the virtual intersection curves of your surface transition are mathematically equal to 0 in the second derivation.
Sounds complicated, but it’s simple because this second derivation is represented by the 2nd control point of your curves or the row of control points of your surfaces.
Uhm… 2. control point row without the starting point row.
G0-G1-G2…
Ideally, you should be able to control 3 points or rows of points for a G2 area transition. G0 (position) G1 (tangency) G2 (curvature).
Now our surfaces usually are connected to other surfaces on the other edges. Using degree 3 geometry would mean that you need all available points for one transition. As soon as this doesn’t fit on the other surface edge by pure cance, you’re stuck. To achieve CC on this other edge you ( or Rhino) would need to move the same control points who maintain the CC on your first edge. This pretty sure will destroy CC here.
In order to be able to control the transition to this second surface without affecting the transition on the first edge, 3 more control points make sense. That brings you to grade five geometry which would make it much easier…
G0-G1-G2_G2-G1-G0
Hej JimCarruthers,
I responded to digiformer’s comment, which I believe is a valid one.
Cheers!
digiformer is right. Apple, like most top-tier brands in their respective industry sectors, do things to the highest perceptual quality possible. A surface modeller or plastics tooling engineer not capable of realising why G2 and G3 continuity are necessary has no place there.
Examine the sections provided to suppliers for Apple Watch accessories. Notice something?
The most important thing is to get away from approaching every modeling problem as “how do I get a surface between these edges?” You need to work from the major surfaces to the smaller blends/fillets that connect them, then these issues become much more manageable.
Seriously, please, stop trying to insult “jim,” I’ve disagreed with him from time to time but he’s been using Rhino for about 20 years now and clearly has forgotten more about this topic than anyone else here knows.
And yeah yeah Apple products are made with very high surface quality. And you know how they do it? Brute-force point-editing, no special “tools,” that’s what real “high end” surfacing is.
Yeah that photo in now way shows an abrupt G1 transition, nor anything that does not look exactly as intended.
Hmmm … doesn’t that mean that a curve has zero curvature, that is that it’s straight ? 
absolutely…
dont mess curvature with curvature continuity…
a crv with a crvtr value of 0 is straight. A curve with a curvature value of x has to be continued with a crvtr value x curve to get a CC continuous transition…
G2 continuity requires the second derivative is continuous across the edge. It does not require it be 0 which would be zero curvature / infinite radius.
Hej Toshiaki,
it’s always about quality curves and patch layout. Maybe you want to try the principle below; it’s the typical solution for a Y-branch.
Here’s a quick example of that principle Y-junction of three tubes with equal diameter.3dm (326.2 KB)
It doesn’t matter what the material is or what the manufacturing process is. There is no material or process that can be managed with sufficient accuracy to produce the G1 seam that you imagine is going to appear on the manufactured part. It is physically impossible.
It is easy to demonstrate why this is true. Enclosed is another model where the G1 seams that you hung a bunch of arrows on have been replaced with G2 blends. Now_IsThisG2.3dm (1.1 MB)
The difference between the G2 version and the G1 version is less than 1 millionth of an inch. What material or manufacturing process is going to be able to capture physical differences that tiny?
I gave you one example where that would be true, but I didn’t generalize from there to say there is no difference in all cases. The point was G2 doesn’t guarantee quality. You can make good or bad looking G2 and good or bad looking G1. You can even make G1 and G2 that look the same.
