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cache
04-13-2004, 01:42 AM
Hi again :)

Dont know wether it is possible at all..
but.. Can one turn his poly mesh into a clean nurbs object ?

( I heard that it is possible to extract edgeloops from a (eg. a subdiv(meshsmoothed)) polymodel as a spline, and then with the help of them you can build up/reconstruct the model as a nurbs object..
(not knowing much about nurbs though)

My question would be that is it possible ?

Is it possible with complex surfaces too (eg. a whole, detailed human body)?

are there other/easier methods to make a nurbs obj. from a poly mesh ?

thx in advance!

cache
04-14-2004, 02:25 AM
Execuse me if i may act like one who is hurrying you :blush: ,
but i would like to ask ANYONE who has got ANY info on this, please post a quick reply; as veryvery soon i have to hand in an important paper in school, and this would be an information that would worth gold to me right now, as i'm in panic right now.. :cry:

:>>

thanks guys!

gmask
04-14-2004, 02:37 AM
This is a ratehr application specific question.. if you are in maya then there is a function for this

cache
04-14-2004, 02:50 AM
oh.. my saviour :)

and do you know that is the result a clean nurbs obj ?

'Cause in max (which is the prog. i use) it is possible to turn any kind of polymesh into a patch, and then, patches can be converted to nurbs, but the structure of the result is so messed up, that it is useless (at last for further tweaking)...

so it is really working ?
does this conversion in maya have an "identical/specific" name perhaps so i can search for it on the web ?

thx very much !


edit: i did a quick search on this, and i found this:

"CONVERT: Allows you to convert one type of modeling into another type, HOWEVER!!!! It is NOT possible to convert Polygons to NURBS, only NURBS > Polygons"

quote from : www.caad.arch.ethz.ch/CAAD-Extern/ uploads/1238/Modeling_in_MAYA.doc

hm.... :confused: :hmm:

gmask
04-14-2004, 02:58 AM
Sounds like it works much in the same way as max.

It creates a Nurbs patch model as complex surfaces usually cannot be represented as a single nurbs surface. I have found that if you seperate the poly model in advance to sort of tells the software what the boundaries should be and then it works much better.

For a character it makes sense to break the poly mesh at the limbs, waist and neck.

Actually in maya you have to convert to sub-d and then you can use SubD to NURBS in which case it helps if the poly mesh is all quads.

cache
04-14-2004, 03:04 AM
hmm... interesting
you are helping me a lot :)

Could you please answer one more (hopefully last:)) question, which bugs me personally as well:

so if it is possible to construct something with polys (for ex. just from quads), and then turn it into NURBS, which is an industrial standard as we know, then - we could say - that
polys (or at least subds) are industrial standards as well ??! (now that the conversion is avaiable)

thx for the reply!

gmask
04-14-2004, 03:12 AM
Hmm I wouldn't go so far as to say that.. furthermore all nurbs are not created equal.

The main issue with any modelling type when talking about industrial design is the accurracy at which you can create the surfaces.

cache
04-14-2004, 03:14 AM
"furthermore all nurbs are not created equal"

maybe it is my wrong english :blush: , but i seem not to understand this sentence of yours :cry:

could you please... ? :rolleyes: thanks!


EDIT t: one more question if you dont mind and if you have time...

what do you think would it be a big change in 'modeling world' if one could turn any kind of polygonal mesh into a nice and clean Nurbs object ?

Or wouldn't it even matter ?

So, basically What would the consequences be ?

i'm very interested in your opinion about this
:bounce:

gmask
04-14-2004, 03:22 AM
Just because a program has nurbs modelling does not mean that those surfaces are of the same accuracy as those in a program designed for industrial design.

cache
04-14-2004, 03:25 AM
hmmm i really thought that all modeling program that can handle nurbs is capable of producing a highly-accurate model with it that can deal with industry standards... :surprised
/me is not just simply surprised, but is extremely suprised :>

gmask
04-14-2004, 03:41 AM
I'm not an expert in industrial design but consideirng that there are a hugh number of CAD programs out there versus the number of 3d animations packages then I would assume that there is some reason why. Many of these are even more expensive than the 3d packages we are familiar with.

My point was that in regards to simply converting polygons or sub-d's to nurbs then the accuracy is only as good as the original model. If creating industrial design directly in nurbs is preffered because of the accuracy for curved surfaces then I think it is safe to say that the reason for tis is becuase most over methods are not accurate enough or do not allow enough control.

You can use any model type for industiral design but depending on the application it may be more or less difficult or impossible to control the accuracy of the curves .. the difference being if you are making toys versus jet engines one has a larger margin for error than the other.

cache
04-14-2004, 03:47 AM
wow all I can say: Thank you veery veery much! You really helped me out!!!
:lightbulb

:bounce:
:)

gmask
04-14-2004, 03:54 AM
Originally posted by cachee
wow all I can say: Thank you veery veery much! You really helped me out!!!
:lightbulb

:bounce:
:)

Here's a good link discussing why all NURBS are not the same

http://www.rhino3d.com/accuracy.htm

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