Problem using Preserve Isocurve Direction

Experiencing a weird issue when using MatchSrf. I’m trying to create curvature across two surfaces while preserving isocurve direction, but I get a crazy error. I only seem to be having this issue when both curvature and preserve isocurve direction are enabled.

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Hi Thomas - please post a file with the two surfaces.


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Jaguar_E-type coupe_1961_Model_duplicate.3dm (8.1 MB)

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Heh - that is pretty spectacular. I blame the target surface, I would not make that with these two edges tangent to one another:


Rather, make that surface a trimmed one




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In the far past I used to try this method, it never worked very well. Hence, ‘networksrf’ is always the best method.

This is not true. There are certainly cases where that command is helpful but it is by no means always better than using MatchSrf.


I didn’t say it was perfect, but matchsrf has enough unexpected transformations that networking the data instead will usually create a better transition – regardless of pros n’ cons of the relative compromises.

@Thomas_Stevenot What is the design intent?

Design intent dictates possibilities.

I adjusted the render mesh to see better:

:face_with_monocle: :thinking: :thought_balloon: fill the hole? with additional surface? or current surfaces?

had to increase precision to fit those weird degree 5 curves:

next step, i’m modding the original data while maintaining precision:

next step networking new srf from prev mods:

rebuilding and sacrificing some precision:

now for assumptions of the adjacent data:

almost done:

Jaguar_E-type coupe_1961_Model_duplicate_emod.3dm (5.7 MB)

This is also true:

Depends on design intent really.

Isocurves are relative, and the flow can be manipulated many ways via ‘netwrksrf’. Curve networks are powerful that way. There’s many hidden techniques I used however.

Depending on design intent, the tolerance deviations from original design data can be bent like a spoon in many ways.

It’s up to the designer to decide, and hard to make the decision for them.

Sometimes, designers don’t want to care about “isocrvs” , but the way they flow is literally entirely controllable via ‘netwrksrf’.

If the designer wants the iso’s to flow differently, then depending on intent, they can be done so.

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This is all amazing help so firstly thank you. I guess to answer the question about intent, this is mainly an exercise for me to learn how to make ‘high quality’ primary surfaces that allow for editability. I’m very much a beginner to rhino and surface modeling, so bare with me. I have been told to avoid using things like networksrf because it creates a very high point count making the surfaces nearly impossible to edit or manipulate. I was advised to stick to things like EdgeSrf and MatchSrf so that I could build and connect surfaces with curvature while being water tight and editable. Also making a trimmed surface… does that not effect the edge quality as well? Again thanks for the help, I was not expecting so much assistance.

Hi Thomas - you are basically on the ight track, I think, but having adjacent untrimmed egdes that are tangent willl cause problems in general. Often simple trimmed surface is a lot more tractable than a convoluted untrimmed one.

The reason that is a problem is that the surface normal is calculated from the U and V direction vectors at any given location. If U and V are parallel, as in the case of tangent edges, then the surface normal is undefined at that location, and things no longer work well.


Ok excellent. I’ll get to work on it. Thanks again.

Network surface method is where the power is, if you understand the 4 sided nature of untrimmed surfaces.

Yes, it has it’s own set of complexities, but when ‘workflows’ are boiled down to a recipe, then it becomes much easier to repeat success.

The ‘high point count’ is a relative thing that can be controlled and rebuilt.

It’s all about maintaining control over deviations of original data. Obviously if you control the design intent, then you will have even more control over decisions associated with deviation allowance.

The surfaces aren’t nearly impossible to edit or manipulate if you can learn to be a master of the network surface workflows – it’s quite the opposite.

Yes, sometimes you might want to use ‘trimmed’ data, but that’s merely a constituent of network surfaces – all surfaces are comprised of a wire frame network of maths, hence network.

This is an ongoing desire regardless of geometric entity format I surmise for most long term goals of 3D solid modeling methods. Although, it’s not as big of a deal as it used to be over 10 years ago.

3D printer slicer software for example seems to handle meshes better these days without being ‘water tight’. And while water tightness is preferred in most cases, CAM programs handle open-polysrfs just fine too – it all depends on the methods of the user.

EdgeSrf and MatchSrf, only go so far. Eventually, the power of networking curves together to combine or merge data, is the ultimate thing to do – maybe not for everything, but is a powerful addition to any method, whether you trim the data, and/or match it or use edges etc.

It all depends on results, and intent. Some designers don’t even want to invest mental capitol into the underlying fabrics of surfaces etc, and that’s understandable.

The game is changing alot too, with sub-D’s and shrinkwrap, quadremesh, etc.

Yes, there’s pros and cons either way. Trimmed surface can be more difficult to manipulate after they’ve been trimmed, because of the sequence of rules that govern their behavior. The trimmed edges are problematically unpredictable through particular transformations of adjacent geometry.

It all depends on where the path takes you as a designer, and how the geometry evolves over time through various iterations and transformations.

Pros and cons either way, trimmed or not-trimmed.

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Wow, thank you for this breakdown/explanation. If I might ask, where do you recommend learning more about Rhino and/or modeling concepts like you have just discussed? I rely mostly on youtube, which feels pretty scarce in general. Also, what kind of projects do you recommend taking on in attempts to build skill and learn? I feel like I should be paying you for how helpful you’ve been. Maybe I’m just not used to the Rhino forums.

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Hi Thomas - I would start here

just to get started, and then look around on the Learn page. and some of Sky Greenawalt’s videos



Well, back in the day before youtube really took off, I had to learn from the very few training “tips and tricks” videos that existed at the time, plus I read the ‘help docs’ on a daily basis, for years n years like my life depended on it – cause it kinda did.

Also, I emailed the Rhino peeps quite a bit in those days, before the forum really took off. I used to access the “forum” in it’s infancy through mozilla thunderbird software – ah the good ol’ days.

The ‘network surface’ concepts I’ve discussed slightly here in the forum is based on years and years of my own struggles figuring out how to approach certain things associated with reverse engineering very highly complex organic compound geometries – so some of my concepts are trade-secrets per say.

But I’d love nothing more than to make Rhino better and make things faster and easier for everyone, cause I’ve recently decided that Rhino is the best of all CAD’s – considering everything. And I’ve decided to do what I can to put my heart into it and see where it all goes.

Cause the alternative CAD’s really don’t impress me that much with their endless fees and perpetual lease contracts.

I really like Rhino 7 with the new tools, and really look forward to R8 and the new WIPS.

I don’t use youtube much for learning Rhino cause it really wasn’t around or definitely weren’t many videos when I was a beginner. But I do check it out from time to time to review anything I stumble on.

I use youtube for learning pretty much anything it seems, so I do highly recommend it, I just don’t know any particular channels to rely on.

Although, @pascal is one of the best sources for sure, and the rhino help docs are some of the best around, and the new “learn” page is awesome that he mentioned. Plus I’ve also seen some of Sky’s videos he mentioned.

I’ve thought alot about maybe making some videos of my own flavor someday, which I keep thinking more and more about.

Well, my number one rule would be the project needs to be important to you, that way it will drive and motivate you every hour you spend every day, even in your free time in your mind you’ll dream of ways to create things with every new feature of Rhino you learn.

Alot of CAD’s are similar too, I remember dreaming about different ways to accomplish things in different CAD’s (still do every day) and imagining if certain things would work for weeks on end, and sometimes things fail, but other times things lead you to tremendous successes.

Every user is different though, so user techniques will lead to different tendencies and down different journeys.

I’ve noticed alot of users here are real deep into Grasshopper, and I’m still scratching the surface on it, but since it’s basically merged into Rhino now, I’m beginning to put more energy into it – slowly.

I’m kinda taking my time with Grasshopper, but I really like what I’m seeing with it, and look forward to it’s further development.

Also, I recommend spending time here in the forum cause I’ve learned alot here just reading and asking questions and even from having different debates n’ stuff :grin: