Manipulating complex surfaces

[propstuff]

The result of lofting is often not a single NURBS curve/surface, but a Group or a Solid Addition of a number of individual curves.

Likewise, if making a symetrical object, I usually follow the normal procedure of making one half and mirroring to ensure both sides are the same, then Adding to get the desired solid.

The problem is that none of these objects are "An Object", they are simply two or more objects "glued" together. This is evident when you need to edit them. Instead of the 3D Reshape tool displaying the verticies on a single surface, the surface of the addition resolves back to its original pieces which can only have their verticies edited individually.

Trying to tweak the verticies of NURBS surfaces that abutt other surfaces and keeping the edges joining seamlessly is "difficult" -to say the least.

I've tried to extract the Surfaces of solid additions but only managed to produced the same sort of result: a group of separate surfaces.

How do I get *one* reshapable surface from a number of surfaces??

cheers,

N.

[tom kyler_dup1]

Propstuff...the "connect/combine" tool will allow you to connect surfaces together, not just lines. When you use this tool you'll have several options (9 times out of 10, you'll use "tangency matching". Once the surfaces are connected, they will be editable as a single surface.

For example, let's say you create a half a surface, say a hood scoop for a car and then mirror the other half...and then let's say that there's a visible seam between the parts and adjusting points isn't really practical at all. Then you use the connect/combine tool and you'll get this option for "tangency matching". and VW will make the seam tangent (or seamless) and create a single surface for your editing pleasure.

Furthermore, if you then select "create interpolated surface" then you can manipulate the surface much more easily. Complex surfaces become a snap. Enjoy!

[ 06-14-2004, 05:58 PM: Message edited by: tom kyler ]

[propstuff]

Hi Tom,

Unfortunately my experience of trying the Combine/Connect on NURBS is, more often than not, the good-old " You have tried to make a surface which cannot be computed" (I forget the exact wording) error message. (Like my old friend "Edge filleting has failed -try something else")

Being a bit slow on the uptake, I've only just discovered that messing with the surface Normals makes things behave better, but still, Combine/ Connect is not a winner in my experience.

cheers,

N.

[tom kyler_dup1]

Sorry to hear that propstuff. I've had real good success with filleting and joining surfaces, I come from a nurbs modeling background as well as a mathematical engineering background and it helps me model (that and tap dancing through numerous VW workarounds). The power is there in VW, but successful nurbs modeling means abiding by the mathematical rules. And I caught a post by Biplab saying ...."We didn't want to have a large number of commands to create NURBS surfaces." Unfortunately, to really get nurbs to do want you want them to requires a bit of understanding of what's going on behind those commands. Connecting nurbs is very numerically sensitive. I think a good book on modeling nurbs in vectorworks is in order....

[ 06-14-2004, 06:21 PM: Message edited by: tom kyler ]

[propstuff]

Back again,

I've been doing some more testing on this and tried a basic shape.

I made a cylinder& tried to fillet it. As usual the Fillet tool failed............

I made a new file, tried again; this time the fillet worked. (very frustrating) Next I converted the fillet to NURBS to manipulate and the result was a Group of NURBS: a Circle in the middle, the Fillet itself, and a cylinder around the outside.

These successive surfaces are tangential (neccesarily) and abutt each other exactly.

I then tried to combine them into one single surface. I was completely unable to get them to combine with the Connect/Combine tool. It "appears" the Combine tool only works if the NURBS are not touching (?)

So, how do I turn these into one NURBS surface?

Biplab ?

cheers,

N.

[tom kyler_dup1]

I agree propstuff, I've been experimenting too, and have found inconsistent results with the combine/connect tool. I fully understand the tool and how you can specifiy tangency matching for edges as well as iso-parms...and I also understand the order in which you select edges or isoparms affects the final shape and how they're connected. I've gotten it to connect surfaces that are touching as well as surfaces that are not touching using the 'blend' mode. But it won't seem to work on the simplest of surfaces. There must be some more information regarding the degree of the curves, or maybe the alignment of the U or V edges or the number of iso-parms or points that is affecting the ability to connect surfaces. Maybe we can send some examples to Biplab and get some input. I feel this is one of the last areas to figure out for me to really go to town with nurbs. Biplab?

[ 06-15-2004, 07:50 PM: Message edited by: tom kyler ]

[propstuff]

Biplab,

can you give some guidance here?

As per the manual I have tried curvature and tangent matching (along with every other option) but the surfaces will not connect in either VW10.5 or the VW11 demo.

I havn't found a reference to iso-parms in the Manual and I'm ignorant of their relevance to this problem.

How do I combine 2 or more NURBS surfaces into one?

cheers,

N.

[Biplab]

The problem with matching surfaces is that - the surfaces need to be untrimmed surfaces. You can find out whether a surface is untrimmed or trimmed - by pressing the unTrim button in the OIP of a NURBS surface - and see of the surface shape changes.

If your surfaces are untrimmed (or naturally bound as they are called in math) - and they still do not match, please send the file to me. Send me at biplab@nemetschek.net

[tom kyler_dup1]

That definitely helps Biplab, I'll admit, many of the surfaces that I've tried to join have indeed been trimmed. I did re-order some of my operations and have since had more success with the connect/combine tool. I guess I'll have to adjust my modeling strategy.

[ 06-17-2004, 08:15 PM: Message edited by: tom kyler ]

[propstuff]

I went back to my simple filleted cylinder Biplab, and the top Circular surface which had been created by converting the Fillet to NURBS was, in fact, a trimmed surface.

So I tried Extracting the curves and Creating a Surface from Curves; this produced a Trimmed surface. As did Create Planar Caps and also creating a separate NURBS circle.

What alternatives have I missed for filling in that top surface, or is converting a filleted cylinder to a single NURBS surface something which can't be done?

Also;

The success or failure of many of these operations rests on the order that individual operations are done, or even the order that individual parts are selected (!).

Is there some way of predicting which order is "correct" without having to go through the time consuming guess-and-hope process I'm currently using?

N.

[tom kyler_dup1]

Propstuff, modeling strategy definitely plays a part. As far as your filleted cylinder goes, I'm not sure you'll have success creating a single editable surface using seperate surfaces, it's a real fight. I was able to use the polyline tool (fourth mode) to create a cross section of a filleted cylinder, the go to plan view and duplicate array (polar) to create 8 total sections. You can then use the skin tool (select eight consecutive then check the "closed" option) to create a single surface with editable points.

For now, I've quit trying to figure out how to combine surfaces and am trying to create complex surfaces with more control U and V curves instead.

[propstuff]

quote:

---

Originally posted by tom kyler:

You can then use the skin tool (select eight consecutive then check the "closed" option) to create a single surface with editable points.

---

Hey Tom,

now I'm REALLY confused ;-)

I've never heard of a "Skin" Tool -though I like the sound of it a lot.

It doesnt exist in the index for either VW10, or the Demo of VW11. (although I did find an entry for "Scuba Diver" in the index.............)

???

cheers,

N.

[tom kyler_dup1]

Sorry about that, I use too many 3D programs I think. It would be the loft tool in Vectorworks. I'm just used to calling it the skin tool from Electric Image Universe, which is a nurbs modeler.

In fact, you can go to their website, www.eitechnologygroup.com and go to the support link and download their online manuals (they're PDF format) there's two manuals, one for their animation system and one for their modeler. The PDF for their modeler (which is nurbs based) is very thorough and will teach you many concepts about nurbs modeling. some of the stuff won't apply to Vectorworks because their tool set for nurbs is a little more robust, but about 90% of the materials apply and the principles of proper nurbs modeling abound throughout and will help you immensely I believe, particularly the section titled "3D tools palette"

[ 06-18-2004, 10:36 PM: Message edited by: tom kyler ]

[propstuff]

Yeah, well I guessed that's what you meant Tom, but I still like the idea of a "Skin" Tool. :-) Being able to just select a group of surfaces and combine them in one go would be very nice.

The "uberNurbs" seem (on short inspection) like a highly desirable thing. Being able to manipulate different groups of Verticies at differing levels of "resolution" would be a bonus.

TouchCad also seems to offer this type of editability -although in a Boat-building sort of orientation.

I'll have a good look at the manual later.

cheers,

N.