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cant extrude


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Hi

Why cant I extrude (push pull / tapered extrude / normal extrude) this nurbs surface?

Want to create ribs for a furniture piece

Steps i followed:

1 Created the model

2 create contours with the contours tool

3 offset the nurbs curve inside with 20mm

4 made from the outer nurbs curve a nurbs surface

5 trimmed the inner curve from the nurbs surface

6 try to extrude, failed.

ubbthreads.php?ubb=download&Number=10960&filename=ribs.jpg

Step 6 went well for several other ribs I tried to create, but not with this one.

Somebody knows why?

Other thing that often happens, but I cant replicate at the moment:

1 Create contours from a solid or nurbs surface.

2 Offset the nurbs curve to a specific site with something like 10mm.

3 9 of the 10 curves do that too the right side, but 1 or 2 do it to the wrong side (not to the inside but to the outside)? Why?

Its not because of the curve direction, I checked that.

Edited by Buzz Lightyear
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  • Vectorworks, Inc Employee

Wouldn't shell as a whole for me either, however I was able to slice it up with the split tool into 4-5 parts and each part then shelled separately. Then they cooperated with a Solid Addition command. Test file attached.

Not sure why the slicing is required however, submitting it now to see why that would matter.

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I would suggest using the Extract Surface tool with the "Select Faces" and "Create Planar Surfaces" options turned on. It will create planar polylines in 3d space that can be extruded easily with the regular Extrude command.

(This is where VW falls apart in 3d. The NURBS surface and a closed polyline in 3d space should behave the same.....)

Kevin

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  • Vectorworks, Inc Employee

Spoke with engineering as to why the shell failed, it turns out this particular NURBS surface was a "trimmed" NURBS surface.

If you select it and look in the OIP, you can see that it says "Untrim" (which we don't want to do) but that revers it back to the original shape, which was a rectangle. It also reports that this NURBS surface has only 4 vertices, which is not the case, but its actually reporting the original vertices of the trimmed rectangular surface.

In this example it was simple enough just to convert the un-shell-able NURBS to polygons, add surface to combine all the polygons, then extrude the resulting poly to the desired thickness, but I am submitting a request for a more informative error message if a scenario like this comes up in the future, where there is no way for the user to know why the operation failed.

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Jim,

Are you saying that a trimmed surface can't be shelled? (I think you are but I just wanted to confirm)

Rhino will do all sorts of things with the original surface including extruding it, rebuilding it etc..

VW's NURBS commands need to be more robust. The obvious solution in VW should be to use Rebuild NURBS but it won't even work on a trimmed surface.

Extract is still the most efficient solution.

Kevin

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  • Vectorworks, Inc Employee

The answer I got back was "Not all, but most."

I agree with your concept but I have to submit specifics, a feature request that just reads "All NURBS commands need to work in every possible situation" will go nowhere. Anytime anyone comes across a specific scenario where Vectorworks' behavior regarding NURBS is inappropriately handled, please get my attention and I will submit it to be corrected.

I would like to be able to submit large sweeping things like that, but I have to grind it down to very specific functionality improvements.

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Jim,

I'm sorry if my post came across that way. That wasn't my intention.

I'm trying to understand why this particular surface causes trouble in VW. Is it just a bad surface?

If I extract a planar surface, the surface that's generated works fine for any operation I've tried (it will shell, extrude, convert to NURBS and then trim). Part of the challenge is as a non-technical person these surfaces look the same. Clearly VW knows how to "fix" the surface when it extracts from it.

When the whole screen plane / layer plane mess was introduced I assumed that the code had been re-written so that 2d polylines were being drawn as NURBS behind the scenes. I guess I assumed this because various NURBS tools that existed previously disappeared (NURBS circle for example) and because many other software packages see 3d polylines as NURBS curves.

I keep drawing comparisons to Rhino because I find myself using it more and more in tandem with VW. It is more robust and is directly competing with VW when it comes to curve and surface modelling. I don't think its an unreasonable comparison. Nor do I think its an unreasonable to wish for similar robustness in VW. As far as I can tell the NURBS tools in VW are pretty much the same as when they were first introduced.

Kevin

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  • Vectorworks, Inc Employee

No no, it wasn't bad or incorrectly made at all (which is sometimes the case, but not here), just something Vectorworks wasn't able to handle withing the current "rules" of the Shell tool.

Also, I don't mean to say that it is unreasonable to wish for the same robustness as another application, just that if that is the wording the request gets I can tell you from experience that it will not be accepted as a feature to be added.

Currently, there isn't a way to suggest a large, sweeping change to an existing component of Vectorworks either internally or externally.

For example; the conversations that have been had here on the boards about our UI. It is ABSOLUTELY true that Vectoworks would benefit dramatically from an update to its standard UI, taking advantage of the high level of screen real estate that was unheard of in the time that the UI was originally designed. However, there isn't a direct request/suggestion pipe that leads to this sort of broad overarching change.

I will soon be endeavoring to change this fault in our process, (after my current all-time-consuming project that I can not go into detail about yet is complete) but for the time being, when I post clarifications like my previous one, I just mean that the phrasing of the requests needs to be altered and refined in order for it to be accepted into the current revision process.

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  • Vectorworks, Inc Employee
When the whole screen plane / layer plane mess was introduced I assumed that the code had been re-written so that 2d polylines were being drawn as NURBS behind the scenes. I guess I assumed this because various NURBS tools that existed previously disappeared (NURBS circle for example) and because many other software packages see 3d polylines as NURBS curves.

Apologies, I hadn't noticed this part of your post earlier, I will address it here.

Actually, almost nothing about 3D objects was changed in any way to accommodate the screen vs layer plane system. This was due to the current way features are selected, tested and implemented. To you and I, it is very obvious that altering the way 2D and 3D objects are displayed in a given "mode" will dramatically affect most if not all of a hybrid modelling process, but this was not noticed during the implementation of the task.

It wasn't an intentional decision to make parts of that system confusing or clunky, just a side effect of focusing on some smaller portions of how it was implemented while the implementing engineers were unaware of others/the larger picture. This is something I would like to see corrected in the future, however it will take some time and effort, I only have so much pull but I plan to use all of it.

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Spoke with engineering as to why the shell failed, it turns out this particular NURBS surface was a "trimmed" NURBS surface.

If you select it and look in the OIP, you can see that it says "Untrim" (which we don't want to do) but that revers it back to the original shape, which was a rectangle. It also reports that this NURBS surface has only 4 vertices, which is not the case, but its actually reporting the original vertices of the trimmed rectangular surface.

In this example it was simple enough just to convert the un-shell-able NURBS to polygons, add surface to combine all the polygons, then extrude the resulting poly to the desired thickness, but I am submitting a request for a more informative error message if a scenario like this comes up in the future, where there is no way for the user to know why the operation failed.

But why this one failed? I just used the contour command to create 10 contours. Just 1 of them failed to extrude/shell/etc. I didnt trim the surface...

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