Nurbs Hull

# 1 17-11-2012 , 11:16 PM

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Hello,

guys I am back with another problem.. I m working on a tutorial in which I am supposed to add two isoparms then right click and choose hull option... as you can see the image from the tutorial.

user added image

Here below is my example image when I add two isoparm and goto Hull it is showing me around 7 pink lines around my two newly added isoparms..
And if you see the top image from the tutorial he adds two isoparms he gets two hull lines.

user added image

same happens when I choose control vertex.

user added image

Thanks,

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# 2 18-11-2012 , 05:49 AM

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What is the degree that you are building your surfaces at? Are you sure you are building them at degree 3 and not 5?

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 18-11-2012 at 09:26 PM.

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# 3 18-11-2012 , 02:08 PM

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Here is my image it seems like I am using 3 degree.. is there any other way i can check what degree i m using ..

user added image

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# 4 18-11-2012 , 09:43 PM

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Yeah you are creating degree 3 surfaces and the attributes tab is the best way to see the degree, parameterization, and form of surfaces.

However, I have no idea what you are doing to create all those cv's. Seriously I am sitting here and every additional iso param adds one additional hull and one additional set of cv's.

All I can suggest is be sure to reset every tool before you use it in the event you have sipped some odd mode on.

If that does not work then it's time for the sledge hammer approach and close maya and rename your maya folder and then reopen maya to completely reset all your preferences. If the behavior continues after doing this then I'd really need to see the tutorial section and see exactly what you are doing.

I cannot think of how you are adding a single iso param and getting 4 complete sets of cv's and 4 hulls?!?!

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 18-11-2012 at 10:07 PM.

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# 5 19-11-2012 , 12:18 AM

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Problem fixed

Thanks for your help...

I found the problem for some reason in Maya 2013 when you insert isoparms you have to change the multiplicity to 1 it was set to 3 by defualt..: happy:

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# 6 19-11-2012 , 03:42 AM

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I use 2013 and by default multiplicity is set to 1 so you must have accidentally set it to 3. That happens some times.

I am glad you found it. Most of the time when that happens you have to wipe the entire maya folder and start over. It's just faster then trying to find the thing that got borked.

As a general rule in the future when stuff like this happens. Exit maya and just rename your maya folder and reopen maya. This will generate a fresh prefs file with all default settings. Then see if the problem goes away. If it does (and it usually will) then you know something must have happened to the prefs.

What I do is once I have all the settings I like, I make a copy of the userPrefs.mel file. Then if things get borked I just replace the userPrefs.mel with the copy and then i don't have to waste time systematically trying to find the problem.

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

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# 7 19-11-2012 , 09:15 AM

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Thanks, ctbram

and thanks for the quick points..

got another small question is it possible to change the multiplicity of isoparms once it is set...

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# 8 19-11-2012 , 09:23 AM

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Thanks, ctbram

and thanks for the quick points..

got another small question is it possible to change the multiplicity of isoparms once it is set...

Originally Posted by umarzaman

I do not believe you can in Maya. You can try to rebuild the entire surface but I am not sure if that will reset the mult. of all the iso's.

One of the issues with nurbs and maya is from what I can see nurbs support was cobbled in from a more sophisticated package - most likely alias studiotools - but it's an incomplete implementation. So some tools and settings are not very useful. I rarely if ever play with muliplicity. I don't ever build degree 5 or 7 curves or surfaces. Without proper surface and curve evaluation tools (which maya lacks) they are useless. I am guessing they were left in to support importing from more robust surface modeling apps.

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

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# 9 30-11-2012 , 12:06 AM

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Hull problem

Hello, guys I am back with another problem with hulls.

you can see in the picture that when I create new isoparms and goto the hull option it is showing the hull lines but they are very far from the isoparm i created.

It is suppose to be showing the hull lines at the newly created isoparms if i m not wrong...

user added image

Thanks,

Last edited by ctbram; 30-11-2012 at 01:29 AM.

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# 10 30-11-2012 , 12:47 AM

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Hulls do not necessarily line up with the iso params. The hulls are rows and columns of CV's and they do not necessarily lie on the surface but rather influence the surface.

What you do need to know though is as you add iso params you will effect the parameterization of the surface.

What does this mean you ask? Well look at the images.

1. I start with two nurbs circles and loft and you see I get a surface with a parameterization of (8,1) so you see the u range of 0-8 and v range of 0-1. (look in the channel box to the right).

What this means is there are 8 uniform spans in U and 1 uniform span in V. Where uniform mean each span is 1 unit in length.

2. also notice in this next image that there are 4 hulls. Recall that a degree 3 surface must have a minimum of (degree+1) or 4 cv's to define the curve on that surface.

3. Now I added an iso param and note that the hull does not line up with the iso param. Think of it this way. The hull represents a row of cv's on the surface and as we know cv's do not correspond to vertices which lie on the surface for polygons. Cv's represent points of influence to the surface (like little gravity wells pulling the surface towards them) and so just as they do not lay on a curve they also do not lay on a surface.

4. Now look at the parameterization. It still says 8 spans in U and 1 span in V but there are now clearly 2 spans in V.

This means the parameterization is no longer UNIFORM and this can cause issues when you perform other nurbs operations with this surface. Or in other words the first span now goes from [0 to some fraction x] and span 2 goes from just past the fraction (x to 1].

The general "rule" (or "guideline") is that you should rebuild nurbs surfaces after modifying them which includes inserting iso params, or attaching and detaching surfaces. I keep the rebuild surface and rebuild surface options tools on my shelf.

5. In this last image I simply rebuilt the surface with the default settings and use CV's.

The overall shape has not changed (although the inserted hull and iso will shift because by default the rebuild option for cv distribution is "uniform"). So after rebuilding the parameterization shows 8 spans in U and 2 spans in V and all the spans are uniform meaning they are one unit in length.

This has been a public announcement from your friendly SM nurbs buddy. I hope I have not confused you.

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"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 30-11-2012 at 08:47 AM.

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# 11 30-11-2012 , 01:44 AM

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I wish there was more training on using nurb's in Maya. They have been out of favored for so long and are so poorly maintained everyone fears using them. Yet they can be extremely powerful. Especially for hard surface models.

Not many really understand how they work any more and even texts I have read can be full of misleading examples where they do not realize the affects of things like surface parameterization, nor do they even speak of surface continuity.

Many packages with up to date Nurbs tools automate parameterization and handle it far better then Maya. Maya's Nurb's tool set is really incomplete and has some features that do not even make sense with out tools to utilize them properly. For instance degree 2, 5, and 7 curves in Maya are useless without proper continuity control tools that are not in the Maya nurbs tool set. I believe their only purpose is therefore to support data import from more sophisticated nurbs modeling apps like alias - which was called studiotools the last time nurbs in maya were given any attention.

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 30-11-2012 at 06:30 AM.

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# 12 01-12-2012 , 12:26 AM

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Thank you very much that was a really great explanation .. and seriously i have been looking every where for this kind of information but could not find..

And yes Nurbs are little confusing in maya as i had just started working with maya there are many things I dont understand like i was trying to make a nurbs square and its CV points are not merged. And if I try to merge i cant..

Same with the EP or CV curve tool you cant merge the end points.. So its really confusing..

Thanks,

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# 13 01-12-2012 , 09:12 PM

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Hmmm, you should be able to attach, and open and close curves. You can create two types of closed curves (closed, and periodic). An open curve has separate start and end cv's but they can be co-resident (G0 continuity).

A closed curve has a single start and end CV. But this can cause tangent (G1) continuity to break at this point.

A periodic curve has an extra pair of spans that are hidden at the end of the curve to help maintain tangent continuity.

To connect curves you can use the edit curves > attach, or align commands. You can open and close a curves using the edit curves > open / close command.

You are correct in that there is practically no documentation or books on how to properly use Maya's Nurb's tools. They are touched upon in several Maya books (especially from alias/wavefront) up to about Maya 5.0.

Since then I have only seen one text that attempts to cover it - Alias/Wavefront Maya 8.5 - Nurbs Modeling. I believe it's still available but it really is just a rehash of the Maya built-in help manual text with a little bit if fluff to explain what things like curve degree are, the mathematics of nurb's, what curve continuity means (but only talks about G0 (positional), G1 (tangent), and G2 (curvature). It gives almost no practical examples and although I was happy to flip through it in my local book store years ago I would never have bought it.

"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675

Last edited by ctbram; 01-12-2012 at 09:23 PM.

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