c0, c1, c2 and c3?! Yikes!

Ok, now that I have your attention! :slight_smile: I’d like to ask if anyone can provide some resources (book, video, Powerpoint?) for understanding surfacing continuity that is easy to wrap my brain around?

I am a Rhino person; and though out of ID school 2 + years, I still haven’t been able to grasp this important aspect of creating good surfaces (and neither did my stint in school nor have my most recent contract experiences in housewares have presented me any insight).

I am now self-teaching myself SW and am running into this topic a lot.

Thank you folks!

The basics - this is a good visual explanation of where to start.

From a perspective of most production design, you’ll probably never have a good excuse to use G3 unless you are doing class A modelling using Alias (where you have the tools to properly build and evaluate higher order surfaces) and building cars.

Ultimately it’s just a way of evaluating how light will flow across a surface. Tangency will leave a typically visible break on a surface where the 2 surfaces meet. G2 continuity will smooth out that transition, and G3 even further.

The mathematical reason behind that can be seen here:


You can see that where 2 surfaces intersect on a G2 curve, the radius at the intersection is exactly the same between the two surfaces. On a G3 surface, not only is the radius the same, but it is changing at the same rate as the surface next to it, which means the rate of change of the curves matches.

Realistically 95% of product design is still done using only G1 and seldom use of G2.

Thank you for those resources, Mike. So appreciate it. I will look them over now and see what I grasp and get back if I have any questions. I see that the one Core 77 article you shared talks about those darn “zebras”, as I never understood how to read them. Hopefully that should help.

Have a great one!

Think of Zebra stripes as a way of viewing constant reflections off a surface if you were in a giant spherical room and the walls were painted with stripes and your object were chrome.

The stripes will show you how your surface flows from 1 patch into another. You can see the harsh crease on a C1/tangency connection between a surface, or other areas where the surface doesn’t connect smoothly.

If you imagine walking out to your car and seeing a door ding, you would quickly notice it because even if the surface is still very close to level, the angle of the surface will cause it to reflect the light differently and you’d instantly know. This is why even though the dimensional difference between a C1 and C2 blend might be fractions of a millimeter, it can have an instant apparent effect on the design.

I wouldn’t feel too bad, surprised at the number of seasoned design and engineering professionals I have run into over the years with no idea about this.

The core77 resource Mike pointed out is good, and I’ve used it to get the conversation started with some engineers before, one of them got really into it as there are very direct mathematics corollaries. He ended up writing a pretty good article about it a couple years later, I’ll see if I can’t dig it up.

One thing that is often overlooked or not considered, is that generally speaking, higher order surface continuity yields (if ever so slightly) stronger parts, better, flow, greater adhesion, etc. as any forces acting on them are more evenly spread.

I found this resource just now as well:

I love geeking out on surfacing. Makes me wish I still used Alias :~(

Great explanation of the Zebra’s Mike! I also found this one cool article that explains it visually with found real-life objects (scroll down to the bottom): http://blog.capinc.com/2011/06/solidworks-tech-tip-how-smooth-is-smooth/

Fascinating stuff! I am on my way to grasping this! Thank you!

My course at Design engine covers G1 thru G4 from history to visual … Calculus thru to analysis tools

I miss the days of geeking on out ALias production surfaces as well…

whole lot of various resources in one link.

And dont let people tell you “X software cant do it” if you understand the program and you understand the math it can all be achieved some softwares just do it easier…

Use to love hearing people say that you can use alias surface cause they never stitch in solid modelers… and they never wanted to hear that it wasnt the software it was their limited knowledge… same as people saying you cant achieve curvature in solid model packages like solidworks… if you have splines you can achieve it all. But i do miss Bezier based curves and surfaces…

Solidworks 2014 now has Higher order curves that sets up Solidworks too do G2 and approach g3 continuity now.