Working with surfaces
Working with surfaces
(OP)
I recently got a parasolid from another program. As far as I know, it comes as surfaces.
When the file came, it was composed of 5 different sectors (spilt with an edge) but one unparameterized feature.
My client wants to merge it all so that no edge will show and then I need to edit it slightly. Project a few curves here and there.
In my line of work, I have never encountered a need to use surfaces.
Any suggestions as to how to edit an unparameterized surface?
When the file came, it was composed of 5 different sectors (spilt with an edge) but one unparameterized feature.
My client wants to merge it all so that no edge will show and then I need to edit it slightly. Project a few curves here and there.
In my line of work, I have never encountered a need to use surfaces.
Any suggestions as to how to edit an unparameterized surface?





RE: Working with surfaces
Always always always always always always always post the version of NX you're using. Like most softwares, different versions have different commands available to the user, and that will affect any responses you might get in regards to your issue.
Please please please please please try to use terms common to NX. Sectors, split, merge and edit it slightly mean nothing, to me at least, in terms of NX commands. Please be more specific and describe how you plan to change or edit the model. If you can attach the NX file or an image, that would help tremendously. The more we know, the better we can steer you in the right direction.
Tim Flater
Senior Designer
Enkei America, Inc.
www.enkei.com
Some people are like slinkies....they don't really have a purpose, but they still bring a smile to your face when you push them down the stairs.
RE: Working with surfaces
Is it possible to post a shaded image of what you have?
RE: Working with surfaces
If this is the case then you could try un-trimming copies of the sheets. Hint they may all be identical with seperate boundaries. This is somewhat unlikely, but quick to check.
For the same case where you perhaps have to rebuild several sheets into one. The suggestion that you make as it seems to me is that you need to rebuild the surfaces. Firstly perhaps we should start with asking why, and a look at your geometry would be invaluable for that.
Otherwise when it comes to surface rebuilding tools you could try a through curves surface, or using curve mesh, even the studio nxn all of which use curves and edges that you'd take off your existing geometry to rebuild something approximately but not exactly the same over the top of the imported data.
There is another tool called a quilt surface which is intended for similar such tasks. You could try it but I'd warn you that in my experience it seldom gives great results.
Best Regards and sent us something to look at
Hudson
RE: Working with surfaces
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA
http://www.siemens.com/plm
http://www.plmworld.org/museum/
RE: Working with surfaces
How to ask that question, is to ask the how and where your client wants to look at it in such a way as to NOT see internal edges. After all you could just not show edges in you shading settings in model space. They never show up unless there is a discontinuity in the surface when you create high quality images. In drafting you can simply turn of smooth edges in the views.
Cheers again
Hudson
RE: Working with surfaces
Even though at home I have NX5, the version I am using with the model is NX2 (yes, it still exists).
First of all, it will not be possible (as much as I would prefer otherwise) to post any sort of picture. I am using UG in a military base and we aren't allowed to take things out. If it is essential, I might try to bend a few rules.
Secondly, the model that I am working on (which isn't part of what I do on a regular basis) is an exact replica of a Tibia bone. It was imported from another program. Not a product of UG.
The model has to be free of any edges because my client is going to run the model throught an analitical program and the edges will complicate it further.
I would like to hear some more comments. Hudson's first comment has some excellent tips.
RE: Working with surfaces
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA
http://www.siemens.com/plm
http://www.plmworld.org/museum/
RE: Working with surfaces
I had explained the following at length.
Firstly you can probably safely assume that the bone is intended to represent an average so that you have some latitude to rebuild to a tolerance, and therefore simply rebuilding the surfaces with the most suitable tool would be the appropriate thing to do.
I wonder about the analysis whether you need to inquire further in order to better address some issues I mention below. In my experience FEA at least is capable of meshing segmented models perfectly well. They could be putting you to more trouble than it is worth.
Based on the nature of what you described there is still a small unanswered element. You see if you want to create as near to an edgeless surface as possible then maybe you could imagine something like an open ended tube of varying section describes it fairly well. The problem with that is that it is a two edged surface and most surfaces need at least four edges.
Both the quilt as I describe earlier, and the cloud of points are methods that rely to some extent on projecting the points onto four sided boundaries or other surfaces. In part because what you're dealing with creates surface normals that more or less radiate from a central axis I doubt that either method will succeed. You welcome to try, but I think that the projection method in the quilt for example is prone to mapping the projected normals right through to the opposite side of anything that wraps more that 180 degrees. In fact 90 degrees is a much safer place to limit it.
The probable best available method for a two sided surface is a through curves surface using radial sections, or rings if you like. These could use existing edges from your original model or you may choose either to cut sections or extract isoparametric curves off the existing surfaces. Having accessed some initial curves you may do well to rebuild or edit them so that the meet end to end with at least tangency, (G1 continuity), within each section. It will also serve you well if they are closed curves or chain-able with end points that roughly align from each section to the next. Building the surface is simply a matter of selecting sections so that the arrows all point in the same direction. If you have enough sections you can increase the degree making the surface more complex and possibly following the original more closely.
You may get an nxn studio surface to work with one longitudinal guide, but if you lack the license then don't worry as it will probably not be a great deal different than the through curves method.
If you're willing to permit longitudinal seams then a four sided surface such as a curve mesh or one of the nxn studio surfaces would be most suitable for rebuilding your model if all of the above fails to work. with either of these you can force tangency along the seams.
Best regards
Hudson
RE: Working with surfaces
i too have had the thought for a combine face option, which will help in 5-axis CAM.
Adding my cents to the discussion..If you are able to find a nominal surface normal for all the splits, then try using QUILT option
HariharanB
RE: Working with surfaces
The attached is a tibia model obtained from the site below, secret what secret?
http://www.3dcontentcentral.com/default.aspx
Now I have remodeled it in NX-5, I could go back to V18 but I'd have to be bothered and in this case you'll see there's no real need. I have also included the original Parasolid, and another suitable for use with NX-2.
I gather you'll be able to open the thing in NX-5 and at least have a look at how it is built.
The curves that I created were isoparametric, and I used join curves on each section and then created a through curves surface. You turn off preserve shape in NX-5 to lose the seams, and there it is. QED.
Cheers
Hudson
RE: Working with surfaces
That means that I can now post a pic.
This is the first time I am posting a picture. A few times and I might get it right.
Here you go...
RE: Working with surfaces
By the way, thank you Hudson, once again, for a superb attachment.
RE: Working with surfaces
I decided, to keep the body as accurate as possible, that I will place a datum every 5 mm. I then extracted the curve for every datum. I tried using: insert->mesh surface->through curves, and: insert->mesh surface->studio surface. Both gave me unsatisfactory results. The surface was twisted beyond recognition.
Any further advice?
RE: Working with surfaces
Are you doing something basically similar to my posted example?
Are you attempting to get rid of, longitudinal or radial edges from the original?
For this kind of surfacing work most people don't get hung up on associativity in the creation of the surface. So we treat the surface as a base feature a lot of the time and don't always keep any parameters. There are exceptions but they are relatively few. So I wouldn't bother with datum planes if I were you. In my example I extracted isoparametric curves simply imputing that I wanted 50 in the V direction. I did so separately on either side and almost miraculously the ends of the curves on either half happened to line up exactly. It was no fluke really since it happens often that if the surfaces are built the same way on either side then they will divide up very evenly. In your case in the original data is less regular then just take a series of sections at even intervals which you can do in one command to extract some curves which you should be able to join to form closed sections during the same operation if you wish.
When it comes to accuracy in my example I was able to get within 0.083 mm of the original. Which for most analysis purposes should be more that close enough since the meshing process performs some approximation in any case.
In the case of what you're doing my only concern is that your bone may take in the joint on either end which could present some other real difficulties. I'll leave you to think about that because it may not be necessary to worry about at this stage.
Oh by the way curve mesh will only do four side surfaces. You would have to accept seams per the data I downloaded at the beginning of the example that I sent you. If you do persist pick the curves in order and keep all the arrows pointed in the same direction.
Best Regards
Hudson
RE: Working with surfaces
RE: Working with surfaces
My earlier example was prepared in under 10 minutes, simply because I elected a method that worked very easily for that geometry. Of course you charge an hour for the job, 10 minutes for doing the work and 50 for knowing how!
Let me know what your needs are and I may be able to assist further.
RE: Working with surfaces
I didn't chase any additional surface refinement or even great tangency as I doubt there is call for it. Normally when we talk about surfacing well we mean A-class, which is a completely different discipline where the criteria are almost diametrically opposed to what you asked for,(i.e. you're able to create as few or many surfaces as you need to describe the best looking shape). I just didn't want you to think this represents what I'd call great surfacing practice in most disciplines.
Cheers Again
Hudson
P.S. If I'm going to do the whole job for people I'll have to start soliciting donations to my favorite charity or something
RE: Working with surfaces
If this is the help you normally give others on the forum, then you must be really well liked through-out. I am sure your work place must love you. In Hebrew, using teenage slang, someone might even say Ata gadol!
Your first method really was most accurate and I want to try sloving the problem using that. The bone forms well, until after the peak. Then the sheet begins to bend into itself. Is there a way around that? I tried creating more curves to make the transaction smoother, but nothing I do seems to have any effect.
So for the last time....help?
RE: Working with surfaces
The second method is very similar construction as the first one. I think that you can't get below at least three surfaces. And I think that you have good enough accuracy. To get greater smoothness smoothing the curves can help, but certainly using less curves rather than more is the way to allow more smoothness. I say allow because you generally allow smoothness by sacrificing accuracy.
Now you possibly need to comment more on the second method as it follows what I believe to be your actual data. If you clearly state the number of surfaces and the tolerances that you require then we can talk about the possibilities.
One thing to consider is that you don't want to use other than the through curves method if you need to avoid seams in the longitudinal direction. Another is that the capping surfaces of either end could be rebuilt but not as for the main surface derived from isoparametric curves. The problem with the isoparametric curves around the top and bottom of the shape is that they describe circular topography (like a map), meaning that there aren't four corners. You would want to section the ends to get a four cornered surface in order to build it as a curve mesh. Even then your are correct in observing that you can't get great tangency to the main surface that I built, which in large part is due to the fact that it isn't smooth enough.
I sense that you probably want to understand the way it is done and achieve this task for yourself. If you need more help then post again, but be quick and certain about what you're after.
Cheers
Hudson
RE: Working with surfaces
Thank you very much Hudson!