Fixing Surface Degenerate Points
Fixing Surface Degenerate Points
(OP)
If you're a serious surface modeler, denegerate points (where the iso-parametric curves meet at a point) should be avoided. Degenerate points cause an uneven surface and makes offsetting or shelling sometimes impossible. In addition there will be problems when exporting to another system and issues with manufacturing. An A-class surface should never have degenerate points.
What tools does NX have for fixing these problems? What are the best practices for creating shapes to avoid degenerate points? Or, for example, can the exact same shape in the attached image be created without degenerate points?
What tools does NX have for fixing these problems? What are the best practices for creating shapes to avoid degenerate points? Or, for example, can the exact same shape in the attached image be created without degenerate points?
NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000





RE: Fixing Surface Degenerate Points
Frank Swinkels
RE: Fixing Surface Degenerate Points
The surface I created is made by a single through curve mesh surface, using 2 endpoints and a middle section curve as primary curves and 3 cross curves, which creates a half ellipsoid type of shape as shown in the previous image.
NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000
RE: Fixing Surface Degenerate Points
Make sure the dlx file is in one of the following locations:
1.) From where NX session is launched
2.) $UGII_USER_DIR/application
3.) For released applications, using UGII_CUSTOM_DIRECTORY_FILE is highly
recommended. This variable is set to a full directory path to a file
containing a list of root directories for all custom applications.
e.g., UGII_CUSTOM_DIRECTORY_FILE=$UGII_ROOT_DIR\menus\custom_dirs.dat
Hope this helps.
Frank Swinkels
RE: Fixing Surface Degenerate Points
Cheers
Si
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000
RE: Fixing Surface Degenerate Points
Attached is the NX7.5 version for the ellipsoid. Just for interest I have also included a program for creating spherical caps. I did this some time ago. I was basically looking for an alternative to revolving an arc and to improve my understanding of using rational B surfaces.
Let me know what you think.
Frank Swinkels
RE: Fixing Surface Degenerate Points
There is no NX part in the zip folder and I can't get the Journals to run
Cheers
Si.
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
Frank Swinkels
RE: Fixing Surface Degenerate Points
As I say, the journals won't run and I have no idea to run the dll file? Sorry.
Si
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
There are a number of possible workarounds, probably also general for all surface modelers. ( not listed in priority order.)
1) try divide the shape into 4 sided areas and create multiple 4 sided surfaces.
2) cut away the bad area and replace with a separate surface.
3) "overbuild" the surface such that is still has 4 sides and then trim back to the desired boundary.
Always stay away from using "points" in surfaces. All defining objects should have a length.- All surfaces have four sides. ( -Unless i have missed something serious along the way...)
A small sidenote, revolved surfaces have the noted "degenerate point" but since the shape change is constant, there will be no shape/downstream problems.
Regards,
Tomas
RE: Fixing Surface Degenerate Points
I can run both journals and they execute fine. Do you have the dlx (dialog) files set up correctly?
Frank Swinkels
RE: Fixing Surface Degenerate Points
I Have no ideal what to do with those dlx files, I have never seen one before in my life
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000
RE: Fixing Surface Degenerate Points
When designing objects where the visual shape isn't the critical objective, (such as gearboxes, drive train products, hydraulic components etc etc etc) Maybe we can allow a point to be used to quickly create that surface we need, - as long as we can continue working without the problems noted. ( Shell, blend etc)
I don't know if you have access to the Studio freeform tools or not. In this there is a feature "Studio Surface" which is similar to the "Curve Mesh". The difference is the "target result". The Curve Mesh feature will always create a surface no matter how bad the input data is, the method NX uses is "degree 3 in both directions and as many patches/ segments as needed to match the set tolerances".- If the input data is poor, the resulting surface is worse. The Studio Surface on the other hand tries to match the input data 1:1 ( If your curves are degree 5 single segment, then the surface will be the same ) and thereby create an as "class A" as possible. It will not create a surface if the input data is too poor. It does not allow points to be selected. The Studio Surface does also allow/create combinations of curves not similar to what the curve mesh surface does. It can also create surfaces where the curves lie similarly to what the through curves and sweeps expects.
Regards,
Tomas
RE: Fixing Surface Degenerate Points
Cheers
Si
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
cheers
Si
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
The difficult part is to complain without making people sad... I hope i don't.
If you desire to create a true class A model, you need to start at the very beginning creating as simple ( and large) curves as possible and try to avoid multiple segments if possible. In my perception it's better with a degree 4 single segment curve than a degree 3 , 2 segment curve. ( really can't say why) It will depending on the surface type selected affect the degree and segmentation likewise.
The Sweep15 ( The first surface) is having problems, ( See image)...which probably affects all later surfaces.
The two center splines are non-tangent across the long center plane which makes the sweep have two faces and maybe a number of extra patches. This surface in class A should be a single face , single patch since it is the foundation for all later surfaces.
In the model there seems to be a number of derived objects such as intersection curves, it is better if one can reuse the same simple curves again and again since we are else building tolerance chains.
I.e A surface built from a curve has a fitting tolerance to that curve which in some cases are 0 and some cases the modeling distance tolerance. An intersection curve to the same surface has it's own tolerance to that surface. In the worst case scenario we now have 2 x the modeling distance tolerance deviation, and, a curve whose degree and segmentation which is far away from the simple curve that we started with.
As noted in my previous post the Through curve mesh and the good old swept feature will not bother about the underlying math, both will create 3x3 degree surfaces with as many patches as needed. In the class A surfaces i have seen the objective is to try keep the number of patches down to an absolute minimum. 1-2-3 maybe 4 but if possible not more. Then you can say "I can guarantee this shape to be free from unexpected bumps/ flat spots/ ripple/etc etc". If we have 28 patches we can't state that. We then have to rely on methods like reflection simulation, which in turn is based on the shading facets, which ... is using a tolerance for approximation. Not a real proof in other words.
Regards,
Tomas
RE: Fixing Surface Degenerate Points
Proud Member of the Reality-Based Community..
To the Toolmaker, your nice little cartoon drawing of your glass looks cool, but your solid model sucks. Do you want me to fix it, or are you going to take all week to get it back to me so I can get some work done?
RE: Fixing Surface Degenerate Points
If there is, there shouldn't be! I want to make it completely wrinkle/crease free
Best regards
Simon NX7.5.4.4 MP8 - TC 8 www.jcb.com
RE: Fixing Surface Degenerate Points
www.nxjournaling.com