"Not a valid NURBS shell" error upon boolean unite

[stiltzkin]

I'm trying to unite two nurbs surfaces that were created by extruding circles along CV curves. The surfaces are entirely seperate. Different nurbs circles that were each extruded along a different CV curve. I select Booleans-Union, select the first one, hit enter, select the second one, and it tells me "Error: explodeNurbsShell7 (Explode Nurbs Shell Node): Not a valid NURBS shell." Why does it do this? It's done this a lot before when using boolean operations.

[failure]

You cannot union non-intersecting surfaces. Group them instead

[stiltzkin]

But they are intersecting, and I kind of need to unite them for my purposes.

[joojaa]

Delete history. Also make sure it actualy is a nurbs shape!

[failure]

"and I kind of need to unite them for my purposes."

why?

[stiltzkin]

I need to make a single shaft from smaller tubes (like a Twizzler). Technically I could make a CV curve in the shape of the cross section of the shaft and extrude it along another CV curve, but it would be difficult to get the shape just right that way, and anyway I encounter this problem a lot and would just like to know how to solve it, if I can.

[stiltzkin]

I've tried deleting the history on the objects, and their both definately NURBS.

[failure]

Could you post a screenshot?

[joojaa]

Im not sure if you are aware of the fqact that even after a boolen two nurbs surfaces will remain different surfaces! They dont get combined into one shape.

So the only reason youd need to boolaan is if you need to see trough a area whare they intersect! Anyway you could make suface curves at intersection and trim the shells (wich is basicaly what boolean does).

[jtk77]

Any reason why they have to remain Nurbs?

[stiltzkin]

Yeah I know, I just need to get rid of the intersecting material so that it looks like one peice. I hadn't thought of trimming from intersection curves.. it would be tedious since I have to join many tubes together, but it's worth a shot (though even if it works, I'd still like to know why boolean won't work half the time. I get that same error message very often.)

[stiltzkin]

Well, I'm only keeping them non-polygon to keep they're appearance nice, and I don't know anything about subdivision surfaces. Remember, I may be missing an obvious solution, so inform me. I'll let you know if the above mentioned trimming technique works, but, like I said, I'd still just like to know how to avoid this common error message. Booleans are very useful, and I'd like to be able to use them error free (this happens a lot for all three operations).

[stiltzkin]

Now there's a new problem... a "fatal error" message upon opening the scene. I won't be able to continue with the boolean problem until I solve this new one, which I've posted in this same forum.

[joojaa]

Oh sorry you havent grouped them or anything have you? Or do their boundaries end before the other object ends (you se iif they are coplanar or atleas seemingly so tthen they might not ever intersect fully leaving a thins tripe un booleaned leaving the boolan oeratir inifnitely looking for the output)

Booleans usualy dont work if the surfaces are corrupt, and on nurbs for the following reasons.

Too thin geo, previous interfeering history etc etc. They do work you know they usualy dont work on people who arent used to working on maya tough (for some miraculous reason!).

Maya isnt a solid modeller (solid modeller desent mean ist a bad modeller but rether than it works on solids as primitives), but rather a surface modeller.

Now a surface modeller gives you alot of flexibility, however it also brings the modeller a lot off responsibility too. One couldnt slap a boolean wherever you like in s surace modeller just because the conditions of boolean might not vbe right for one. a solid modeller doesnt have this problem because it keeps track on whats going on, it cant however produce modells with inconsisten normals wich surface modellers rahther easily do!

Example this would fail: showing the end caps of the tube to be booleaned from the sphere! And especialy their normals (wich are inconsistent for a boolean). wich are wrong.

this wouldnt now showing the full geo and correct normals:

And the result. Note that a shape might fail booeans if its not capped boolean if the tube wouldnt dirve entirely trough it you konw and i would hit an edge prematurely (this migh be imposible to notcce since even a failure of 0.0001 would fail).

To cap this up booleans often fail because people dont pay attention to things they dont se! But the coputer needs that info, period! Not understangding this leads many to believe the booleans arent broken. They arent!

[stiltzkin]

Solved the fatal error problem.
Alright, I understand somewhat. I'm going to try and have the tubes intersected in a way that does not involve their ends, since right now their open ends are intersecting the tubes at various angles.

[stiltzkin]

Well I never could solve the boolean error, but I did find a slightly more tedious way of getting done what I wanted. I almost always find another, more roundabout way of getting something done when a boolean operation refuses to execute, so I guess it doesn't completely impede me, but that common error still irks me...

[joojaa]

You must understand that booleans are very intorelanf of ovelap. I mean even the best booleaning software ive seen wont succed 100% of the time. And that program is proe wich is basicaly expensiver than maya, whole workflow boolean operatrion friendly (CSG modell), and it stll has the same overlap problem. And i mean they have literarty spent 10 years on removing boolanproblems and they still cant do it.

SO the key is to be carefull whan you make your boolaens so taht theuy actualy produce something that WILL boelan! not everything will booean.

On the otherhand most things will als long as you dont ask the computer to ake decisions based on hwo things appear. They must be exaclty thet or nothing.