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Set normal vectors on surface boundaries
3

Set normal vectors on surface boundaries

Set normal vectors on surface boundaries

(OP)
Hello,
I'm struggling to solve this problem but I need some help because I don't know how to go on.
The problem regards the construction of a couple of surfaces, sharing one edge (in form of a spline curve).
Is it possible to impose the normal vectors of the two surfaces along their boundaries (in particular along the shared edge) on some arbitrary points near the edge?
Thanks in advance!

jones274

RE: Set normal vectors on surface boundaries

When you say "impose the normal vectors of the two surfaces . . . on some arbitrary points" what exactly do you mean and what is it that you're attempting to accomplish? Could you perhaps provide at least an image of what you're attempting to do?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Set normal vectors on surface boundaries

(OP)
Hello and thanks for your reply.
In particular, I want to take a set of arbitrary points along the edge shared between two surfaces and then, for each of these selected points, I wanto to set the surface normals for each surface, forcing them to respect those imposed boundary condition (the normal vectors).
I hope I made myself clear.

Here's an image


Thanks again

jones274

RE: Set normal vectors on surface boundaries

First off, what version of NX are you using?

Second, are you talking about making these 'vectors' parallel to each other, in other words, are trying to make these surface 'tangent' to each other? If so, have you looked at the 'Match Edge' function?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Set normal vectors on surface boundaries

(OP)
I use NX 10 for Windows and yes, I want exactly to set the tangency between the two surfaces, but only one some selected points along the shared edge. In some other points I'd like for instance to set a fixed angle between the two normals.

RE: Set normal vectors on surface boundaries

(OP)
Is it possible to do this kind of "selective tangency" operation?

RE: Set normal vectors on surface boundaries

Not interactively with any existing NX function, at least none that I'm aware of. Perhaps a custom application could be written using NX Open that would accomplish that.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Set normal vectors on surface boundaries

(OP)
Thank you, this is exactly what I was afraid of :)

RE: Set normal vectors on surface boundaries

(OP)
Hello again,
I tried to step back and watch my problem from a different angle, maybe by rethinking the basis of the problem itself.
Since my goal is to find a logic to reconstruct two surfaces, which may be tangent and/or not-tangent along their shared edge, first I have to understand how those kind of surfaces are modeled via the modeler/cad.

In particular, how are the surfaces containing this sort of "fading out" edge (crease) generally modeled in NX by a designer?
To better explain what I'm asking I think it will be useful to post a couple of examples.





Thanks again!

P.S.: I tried also to ask this in another section, since I'd like to understand the generic procedure (valid for various CAD environments) but they had suggested to ask the specific software sub-forums.

RE: Set normal vectors on surface boundaries

Here's a pretty simple version of transitional surfaces similar to what you've circled above (built in NX9). NX's Edge Blend has a nice option called 'Special Blend At Convex/Concave Y' that allows the blend to flatten out to an infinite value. You should be able to find it in the attached model.

The above examples are variations of my example, however, they are all going to be curvature continuous and would probably be a bit more difficult than my example to build due to both the shape of the larger surfaces and the higher level continuity (curvature continuous or G2) - however, the concept of transition is not much different.

Transition.prt

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

RE: Set normal vectors on surface boundaries

jones274, if all you want to do is a transition and can accept G1 continuity, then Tim's suggestion is excellent. However, the examples you showed are A-class surfaces, which require G2 and G3 continuity. These surfaces require a lot of work. I suggest you go to the website of Autodesk's Alias software and read their excellent introduction and tutorials on A-class surfaces, and try to figure out how to do it in NX. Unfortunately, there is not much learning material on A-class specifically for NX, but most the principals on surface construction can be applied to most high end CAD software.

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

John Baker, since Daimler switched to NX, do you know what software they use for the styling surfaces? NX, Catia ICEM Surf (seems like they were doing) or outsourced to freelancers?

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

When I was at Daimler in Stuttgart last fall virtually all of my time was spent with people from the drive-train group so I have no direct knowledge of what the Body-in-White groups are using. I guess I could ask around and see what I can learn. The only issue is that this sort of information really shouldn't be shared on a public website.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Set normal vectors on surface boundaries

(OP)
Ok, this is much clearer now.
The thing I want to do is to understand the common workflow followed by the designers in these type of modeling (creased surfaces, preferrably made with A-class surfs). I've got an educational license for NX so I'm asking in this section: I honestly don't know if NX is the best tool for this kind of surfaces, maybe I've to ask some Alias users.
Meanwhile I whish to thank everybody for the help, this is much appreciated.

Have a merry christmas!

RE: Set normal vectors on surface boundaries

Jones, if you want to learn A-class surfacing techniques, Alias is the way to go, there is a huge amount of information available. However, in the realm of A-class or "technical surfacing" there is really no preset workflow to follow, it's mostly a black art and depends on each situation. The best way to learn about specific surfacing issues is search on Youtube, there are many videos from car body gurus who explain how they create certain surfaces using Alias. Then, having learnt the techniques, you can then port that knowledge to NX (where possible).

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

John, I'm asking because I'm curious if the surfacing capabilities of NX can compete against ICEM Surf (or Alias) for commercial car body styling. If NX is not used for the styling, are there plans to increase the capability/functionality of NX so that it can be used for that purpose in the future? Has this factored in the decision of Daimler to switch to NX? Because if the styling can be done in NX, then that might lead to huge cost savings for Daimler since NX is all parametric and there is no need for translation of the surfaces.

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

CNSZU,

I seriously doubt if Daimler will ditch their preferred styling/industrial design software in favor for NX. GM, FCA (Chrysler) and Nissan all use NX as their corporate CAD software, however all 3 still use Alias for their styling/ID needs.

In 20+ years I've yet to see an automotive company ditch Alias in favor of any of the 2 major softwares typically used as their corporate software. They still import from the ID software into NX. Can't speak for the CATIA side as I've only dealt with Honda and they also import Alias surfaces into CATIA, or at least they did less than 5 years ago.

NX can create Class A surfaces. The issue in doing so is similar to Alias - you've got to understand how to utilize the tools available to properly create the required curves and surfaces as well as how to analyze the results. That's for what the NX Shape Studio product is used.

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

RE: Set normal vectors on surface boundaries

Thanks Tim, that's very interesting. Do you know why the styling departments prefer to stick with Alias? You'd expect the upper management folks to not be very happy at having a separate software for the styling, they usually prefer conformity. Is Alias that much better or is it simply a case of old habits die hard, stubbornness, and the notion that "we are creative, so we have to be different and use our "own" software" on the part of the stylists?

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

There are many issues at play here. For one thing, even in a company like GM or Daimler, the number of Alias seats is relatively small compared to the mainline CAD system used throughout the rest of the company.

Another issue is that the 'Art' schools where most automotive designers are trained almost all use Alias in their curriculums. Granted, we've done a good job of getting NX and our CAE and CAM software into universities here in the US and around world, including many of them who have traditionally supplied engineers to the auto industry, however the designers attend very different and specialized schools.

Now outside of the automotive world, there are a lot of places where NX is being used for ID (Industrial Design), so the basic tools are there, it's just sometimes tradition is a hard act to overcome.

Now some asked whether NX can compete against products like ICEM and Alias, and while we think we can, we have to also choose our battles. While it may not appear that we've had a lot of success competing for the limited number of seats in the various auto studios, we feel that we can offer a viable solution for the small to medium sized companies, or even some larger ones, who are looking to add ID capability to their organizations who are already using NX for CAD/CAE/CAM but who have not used any dedicated styling software in the past like ICEM or Alias. Potentially there are a larger number of seats available to for us to win than what is currently in use by the automotive OEM's. This is the market that we've positioned products like NX Shape Studio with it's new 'Realize Shape' tool as well as the work that we did in rendering for NX 10.0 and what we're continuing to do in NX 11.0.

To learn more about what I've commented on above, please go to:

http://www.plm.automation.siemens.com/en_us/produc...

And please check-out the list of 'Case Studies'.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Set normal vectors on surface boundaries

Thank you John for the explanation!

NX10.0 Win8.1 64bit i7-3770K 16GB QuadroK2200

RE: Set normal vectors on surface boundaries

To add to John's comments, Siemens has to be loving their position in the auto industry, particularly in the US. All of the big 3 are using Teamcenter now. That had to be a huge win. Plus, it might put them in a great position to keep pecking away at Ford to leverage them off of CATIA. I would imagine that it's not an easy task getting those companies to let go of what they've used for decades. However, they are learning that if they cannot embrace change, then they will probably end up on the losing end at some point.

Not only is Alias being taught to the IDs, there is probably not as many NX users out there that can fully grasp the Class A tools available in NX unless they've come from an ID background. It's not something a typical user can sit down and fully teach themselves like they might be able to do with the more often used modeling tools outside of Shape Studio and Realize Shape. You've obviously been exposed to Class A modeling and the workflows that are sometimes used, so you can imagine the difficulty in trying reteach yourself those dark arts in a different software. Probably not an easy task.

Software choices in many industries is a great and interesting topic, especially when you're able to watch how things have changed over the years. Who would have thought that the former UG would "merge" with SDRC (in terms of software); Autodesk acquiring Alias; CATIA gaining ICEM, etc.

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

RE: Set normal vectors on surface boundaries

In most auto design departments, there are two kinds of surfacing activity: the artsy stuff, and the production stuff.

The artsy folks are creating concepts. These concepts don't necessarily need to be realistic, and sometimes they are deliberatly unrealistic -- the stylist creates a "caricature" to emphasize some aspect of the design. The geometry created in this phase is not subject to any feasibility constraints; it just has to look nice. So, it doesn't matter too much if the shapes are too expensive to manufacture, or the engine won't fit under the hood, or the A-pillars are too thin to support the roof. The geometry is not used for much, beyond the concept evaluation phase. NX can be used to do this sort of work, but the guys doing it don't like to think of themselves as "CAD users", and they probably learned Alias in art school, so NX isn't used much. The market is small, so Siemens probably doesn't care very much about the artsy crew. Though I guess you could say that NX "Realize Shape" is an artsy tool.

Production "class A" surfacing (or "class 1" surfacing, at Ford) is an entirely different game. The geometry is real, it has to satisfy numerous different constraints (in addition to looking nice), and it is used to produce dies and structural body parts. For a long time, ICEM/Surf was the tool of choice in this area. A few companies use Alias, a few use Catia. Toyota and Honda both use internally-developed systems. There are numerous auto OEMs who use NX in this area. I can think of at least two that have switched from ICEM/Surf to NX. As one of the other replies mentioned, there is significant benefit to using the same system in production class A surfacing and in downstream engineering/manufacturing, so the companies who use NX for all of this are typically happy.

The "surfacing" software business does not appear to be a very good one. Lots of systems/companies have gone belly-up. Remember STRIM, and CDRS, anyone? The ICEM/Surf group has been bought and sold umpteen times, and I don't expect Think3 to last very long. Alias got bought, too. Rhino seems to be doing nicely, but it will die if SolidWorks ever gets decent built-in free-form functionality. The problem is that the market is small, but Alias has to have all the same basic infrastructure as NX or Catia -- graphics, UI, saving and opening files, translators, print/plot, etc, etc, etc. So, high fixed costs, and small volumes. The only way out is to charge high prices, which people are increasingly unwilling to pay.

RE: Set normal vectors on surface boundaries

Nice thread.

To compliment BubbaK's post, maybe the most intriguing acquisition is the Autodesk buying Alias, considering that Autodesk already owned 3DStudio Max and Softimage, and subsequently has bought Delcam.
3DStudio and Softimage ( and Maya which was a part of the Alias acquisition) are more intended for game development / image rendering than product development, but all 4 (5?) are also capable surface modelers.
(Softimage has since been terminated)

Back to the original question.
trying to actually design something by assigning vectors ( or angles) along an edge like that is like trying to find the matches in the darkness, difficult. - It's hard to guess what angle or vector will look good.
But, NX does more or less have this function, as a part of the Law extension surface .

Attached is a version of the part Tim uploaded, with both methods included. (My version is quite different from Tim's.) NX10.
The Law extension example is eyeballed towards the spline used in the upper example. The angle is ...


Regards,
Tomas

RE: Set normal vectors on surface boundaries

Yes, going back to the original question is a good idea.

As the previous reply indicated, NX has functions like Law Extension that let you control angle variation. But I doubt that you know what the desired angles are until you see the result and confirm that it looks good. In other words, the correct angle is an output of the design process, not an input.

The ICEM crowd would create this shape by pulling control points (poles) around. In fact, they do everything by pulling poles. So ...
(1) Create a simple surface (one patch, degrees of around 2 x 2).
(2) Split it into four patches, call these p11, p12, p21, p22.
(3) Modify the poles of one patch to produce the non-tangency, while keeping the other 3 joins tangent.
The trick is that moving poles that are two or more rows away from an edge will not affect the edge normals.
(4) If you need a more complex shape, gradually increase the degrees to give yourself some editing freedom. But, the more freedom you give yourself, the more difficult it is to keep the surfaces smooth.

RE: Set normal vectors on surface boundaries

(OP)
Hi,

@Toost: this might be EXACTLY what I'm looking for!! I'm new to NX and didn't know the Law Extension command: I'll start to study it in detail, but it seems it permits to do what I intended to!

@Bubbak: In facts, I have to develop a procedure to impose some angles before building the two connected surfaces.

However, if I understood well, the coomon practice of style designers is to build nice surfaces without bothering with angles, vectors or, in general, without following a "parametric" approach. Is this correct?

Thanks again for your help!

RE: Set normal vectors on surface boundaries

As BubbaK said, for "artsy stuff" designers follow their gut feeling rather than specific angles.
in most (?) cases a design starts as a sketch on a piece of paper where the proportions , the "expression" and the "style" is captured.
Then somebody will transform that into a computer model.It might be the designer or a different person.

the computer model will then be iterated into the final product and during these iterations the "parametric approach" is very valuable, but trying to describe the shape of a car fender in numbers, is... difficult.

Regards,
Tomas

RE: Set normal vectors on surface boundaries

To some people, "parametric" means "driven by numbers". I would say that even production surfacing is not driven by numbers most of the time, and artsy surfacing is hardly ever driven by numbers.

In a larger sense "parametric" might mean "driven by parent-child relationships" (though "associative" would be a better word). This sort of "parametrics" can be very useful in production surfacing. It's nice to have your fillets updated automatically when you move your base surfaces, for example. The automatic update might not give you exactly what you want, but it will still save you some time. In fact, this is one of the reasons that some people prefer NX; systems like ICEM and Alias are not very good at associative relationships.

In your example, I'm still not convinced that entering angles is a good approach. Moving poles allows much more flexibility. But, you understand your task much better than I do.

RE: Set normal vectors on surface boundaries

I worked in plane industry (wind tunnel experimental aerodynamics, optimization of model surfaces) with A class surfaces, and some of best results are combination of surfaces and solids, actually using surfaces to trim off solids. For example the image of car surfacing I would do with trimming solids with surface, that way I can always relatively fast edit surface and repair the shape if needed. This also give flexibility for surface design as there is no need to patch edges of surfaces, so closing actual solid is not an issue. Main "skill" in this method is transitions between already done surfaces, but if it is done properly there is little or no problems.

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