Convert Poly>sub-d, Then Sub-d>nurbs

[vivaldi0]

HELP ANYONE!!!!!!!!!!!!!!!!!!!!!!!!!
For the love of GOD!!!

Ok....I am importing a Poly mesh that I want to refine with under Nurbs and throw on some cylindrical and planar mapping, but I need to convert the Poly to Sub-D's first then to Nurbs. I can do that, but the mesh is like so heavy after converting into sub-d's that going from sub-d's to nurbs is almost impossible (notice I said almost).

I have tried reducing the poly by about 90% and works great. I end up with about a 900 polygon mesh. But, when I convert it into Sub-d's, the topology is really whacked.....Looks nice, but vertices all over the place and in flowery patterns. This in turn, after converted into nurbs, looks really goofy and is just straining my system to death......there is no way i can tweak the nurbs mesh now.

Anyone HAVE ANY HELP?????????????...PLEASE?????????

Even if there is a 3rd party program....cool with me. But i need the original poly mesh to be converted into a nice nurbs surface, whether it is in patches, or a single surface doesn't matter.

[joojaa]

What are you trying to achieve here? In general this si a workflow thats totaly doomed form start. How heavy is the startmesh?

you must undertsand that theres absolutely NO fitting involved in polygon to subd conversion, so if the start surface was relatively smooth to start with youd probably survive very well after deleting every so and so edgeloop. IN genaral models designed for subdivs and thereby subiv to nurbs conversion too realy should be designed that in mind (that is you cant jsut take any highpolymesh and make it subdiv and expect everything to be spiffy).

There are apps that can do this fitting sanely but they are expensive (maya is actualy cheaper than most of theese theese apps), and hard to use. whats your buget... you can get cyslice from headus for about 4000$, and results offcourse it all depends realy much on what your data is like.

http://www.headus.com/au/cyslice/

you can offcourse do all of this in maya with a few gours of manual deletion of loops and mooving verts as you like them... or build the pach model manualy an dfit it manualy.

[vivaldi0]

QUOTE(Joojaa @ 09/04/05, 01:44 PM)
What are you trying to achieve here? In general this si a workflow thats totaly doomed form start. How heavy is the startmesh?

I am trying to achieve a conversion, from poly to nurbs, so that I can texture a model with using cyl and planar mapping.  I have the models from Solidworks, which is where I work.  But not just from solidworks, also VIZ and MAX....these are models I use from a parts manufacturer.  I am a very experience Maya user, so patching and edge looping are no problem for me.  I have gotten the base poly mesh down to a suitable size (from 6000 polys to about 1600)....Now the reduced poly is really perfect (Quads) and looks great after converting to subd's, but the subd surface has areas that are extremely heavy, so converting from the subd to the nurbs surface is the problem.  The conversion doesn't have an option to reduce the surface topology.  The patches are either too heavy (like 8-16 isopars per patch), or too little...simply a 4 sided patch.  I can rebuild surfaces, but it is quite timely and i would have to attach hundreds of surfaces (problem).

If Alias included the SubD to Nurbs conversion option, then what is the point of that?...ask them, I guess.  Yes I need it for this exact purpose.  I have needed it since Maya 2.0 came out.  This is the first time I have used it and am excited it exists.  I would just like to see the same surface topology that I get with my original Polygon model.  I am just not sure of the steps to take, and it sounds that no one else has an explanation for it either, but yet it exists in Maya 7.

Here is a test for you ...Create a standard Poly Sphere, Convert it to SubD's, then convert it to Nurbs.  Look at how the topology looks after that.  Try and make it similiar to the way a standard Nurbs Sphere would look.  Good luck with that.  This is my problem.  I just want a simple surface poly converted to a simple surface Nurb.  Not too much to ask for I think, but yet very hard to achieve.

you must undertsand that theres absolutely NO fitting involved in polygon to subd conversion, so if the start surface was relatively smooth to start with youd probably survive very well after deleting every so and so edgeloop. IN genaral models designed for subdivs and thereby subiv to nurbs conversion too realy should be designed that in mind (that is you cant jsut take any highpolymesh and make it subdiv and expect everything to be spiffy). [SIZE=1]

I do understand that a simple poly sphere or cube converted to a subD, is quite different in look that the original mesh, which shouldn't be.

There are apps that can do this fitting sanely but they are expensive (maya is actualy cheaper than most of theese theese apps), and hard to use. whats your buget... you can get cyslice from  headus for about 4000$, and results offcourse it all depends realy much on what your data is like.[SIZE=1]

4000 buck eh?  Hmm.....I ...uh....doh!

you can offcourse do all of this in maya with  a few gours of manual deletion of loops and mooving verts as you like them... or build the pach model manualy an dfit it manualy.[SIZE=1]

Manual.....yes, I could build my original polys manually, but I am trying to save some time here.
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[failure]

You can cyl and planar map poly model as well.

I once pushed myself right into heavy flames by claiming that it's generaly insane to convert meshes to nurbs for any reason. But I have no problem stating this again though. Just don't do it. You can count arguments and rationalize but it's a dead end.

If you want to save time and avoid frustration build the patch model manualy using mesh as a reference.

When converting from solidworks use iges format which will import into maya as nurbs. All you need to do is to optimize the surfaces by rebuilding.

[vivaldi0]

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Please click the Image to see a larger view and then read the rest of this post.
This might clear up why I want to do this, or not.

1.Original Poly (Good Topology)=small amount of geometry

2.Converted SubD (still good Topology) =small amount of geometry, but could be optimized better. Settings were 12 Faces and 4 Edges PV.

3.Converted to Nurbs (Really no tesselation values here (why?));
I would expect to see some sort of previsualization here from Alias;
I am not coming down on them, but I am expecting this to be looked at, as to why it was ignored as far as some attributes that could be defined before the conversion. Wouldn't it be easy to do some surface analysis and curve projection with the original surface?

4.This is the nurbs tesselation for 4 patches. Good Lord! I could build a surface better than that optimized with a limited amount of spans and curve vertices, with my eyes closed. "Hello!"

5.This surface was rebuilt by me with the rebuild surfaces tool. Easy enough, but i don't want to rebuild 1,000 surfaces after it has been converted. Couldn't they have just had some kind of surface parameterization slider in the convert section?..darnit!

Ok...now you are asking me "dude.....why don't you just stick to poly's?, or why not stay with SubD's?.....WEll, uh....I like NURBS and I like the attributes that go along with them. ALL of the attributes. The fact that i can loft and do so many things with NURBS that I am used to....I can get really nice topology, without having to revert back and forth. Building Surfaces or Rebuilding surfaces to look more organic. Animation features on a nurbs mesh is more reliable than on a poly mesh. I hate triangles and trying to keep quads is a pain in the ***.

I have so many reasons I want to do this, and I can do it, but there should be some kind of user friendly pipeline in order to do this. Or at least some white paper to do it the right way. I need this man!.....Anyone....Alias!!.....Modellers alike...please please.....Mel script or plugin......someone show Alias how to finish a NODE feature and make it right.

[failure]

You are trying to trivialize a non-trivial problem. In fact a rather complex problem.
Producing datasets ( polys ) from functions ( nurbs ) is trivial. Interpolating datasets to build up functions is hard. And it's not mathemathicaly defined in the case of a "bad" or "nonappropriate" dataset - which is mostly the case in real life.

Get some sleep and remodel your objects from the scratch if you prefer nurbs.

Btw topological issues are quite the same with nurbs as with polys. In one case you get a quad structure to maintain, in other - quad patches structure.

In general polys are easier to texture. But not always. Some types of models could benefit from implicit mapping.

Animation features reliability has nothing to do with the type of geometry.

[vivaldi0]

QUOTE(failure @ 09/04/05, 06:05 PM)
You are trying to trivialize a non-trivial problem. In fact a rather complex problem.
Producing datasets ( polys ) from functions ( nurbs ) is trivial. Interpolating datasets to build up functions is hard. And it's not mathemathicaly defined in the case of a "bad" or "nonappropriate" dataset - which is mostly the case in real life.

Get some sleep and remodel your objects from the scratch if you prefer nurbs.

Btw topological issues are quite the same with nurbs as with polys. In one case you get a quad structure to maintain, in other - quad patches structure.

In general polys are easier to texture. But not always. Some types of models could benefit from implicit mapping.

Animation features reliability has nothing to do with the type of geometry.
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You are absolutely right in that, and I do understand that the issues are non trivial. The downstream nature of the conversion process within Maya certainly makes sense to some, but that is exactly what it is; A Downstream pipeline, which generates more feature geometry the more downstream you go. Why convert a SubD to a Nurbs Surface in the first place?.

Why not finish the Bonus tools feature and use the feature that extracts edges from a polygon and converts it to a Nurbs Curve: This code already exists, so why not propagate it to a SubD to Nurbs featurette, or better yet bypass the whole SubD thing and just go POLY to NURB.

The make surface live function is a great tool when you create a curve on the live surface. So, what's the problem with simulating the same process, only automated.

The whole SubD>Nurbs thing is more of an upstream battle that leads nowhere, so why include it in Maya. This is not meant to be arguementative, so please don't take it as such. Building an API plugin that can take the existing code and make it a little more appealing and user friendly for the use of the feature CONVERT SUBD>NURBS, would make sense since it's there anyway. Does anyone really use it? Probably not, but would they, if there was an automatic rebuild function and an attach surface function that we have to manually do anyway to get a surface that just "makes sense".

10 bucks says someone is already in the works for this idea, if not....it's my idea and I own it

Please don't flame me for this post...I was a little tired.

[joojaa]

So if a tool isnt the tool you wanted it to be it must be a broken tool eh? yeswell a hammer is a hammer not a sledgehammer.

QUOTE(vivaldi0 @ 09/05/05, 01:40 AM)
If Alias included the SubD to Nurbs conversion option, then what is the point of that?...ask them, I guess.  Yes I need it for this exact purpose.  I have needed it since Maya 2.0 came out.  This is the first time I have used it and am excited it exists.  I would just like to see the same surface topology that I get with my original Polygon model.  I am just not sure of the steps to take, and it sounds that no one else has an explanation for it either, but yet it exists in Maya 7.

Its for completeness of the tool, its just mathematicaly converts things as is. Nowhere did they claim the conversion leads to less data. Se fitting will reducxe the accuracy of the connversion and maya ofcourse does this with 100% accuracy. And as such im afraid you realy need your modells lighter form the start se thets what the headus app does it fits the surface to a approximate ly same modell. you can allways rebuld the nurbs after the fact giving you a fitting on each individual patch.

They use thet info internaly so they might aswell present it for you. its susefullness is offcourse questionable. BUtthe fact is it is usefull for some 3rd party renderers for the accureate subd surf in question.

Nowe what you end up is the nurbs curve that EXACTLY conveys the subd surface. BUt you want the fit. Well they didnt make a tool like thet. But because the subd algorithm is a bit wonky it will ad stuff on it.

NOTE

IN fact in your image too your subd surface has faar more data than the polygon one because inorder for the subd algorithm to work, everything needs to be quads, okay so what maya does is it adds sund levels untill the target surface gets converted to all quads, with no wonky poles. So the subd surface has atleast one 1 mre level of data than the poly one in the picture (chekit out) Now if you would have split it to all quads you would. note the fact that you think it has only as many points as you se on screen then your mistaken, if you care to look at level 2 poinst youd notice the subd has FAAR moire points to begin with.

in your example case case that means your converting a 12 face polygon into a 240 face subd (wich actualy has 242 points, look at level 2, wich for your shape is dominant) into a nurbs, that has 4860 points wich is for exactness completely sane because each subd face is one nurbs patch worth 81 points

Now if your start shape is such teht it only conveys one level of date then each polygon face would turn into 81 controll points of nurbs at most. Hovever it need s to become all quad FIRST, because nurbs are only quads.

[joojaa]

oh and theese 2 are the nurbs surfaces i do end up with the second one with lower pointrs is the lowest possible sane fit you could achieve.

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click to enlarge!

[vivaldi0]

QUOTE(Joojaa @ 09/05/05, 12:17 AM)
oh and theese 2 are the nurbs surfaces i do end up with the second one with lower pointrs is the lowest possible sane fit you could achieve.
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Yeah, I realized the quad thing everytime i reduced my polygon, I noticed I had to fix faces. The damn .OBJ's I import into Maya are really whacked after converting to SUBD's. I'm not sure what I am doing wrong, but after a conversion to SubD's almost all the faces are separated. I have managed to fix a few models, but it's really after experimenting and then forgetting what I did....I know about the GROUP option in the import section, so that's not it. I just get really strange results from OBJ imports. So after importing the OBJ, I try to Quad them into a better mesh.....It kind of works ok, but not so good. I then have to CLEANUP the model, which fixes a few things. I Make sure the normals are cool, which I usually have to REVERSE and then SET TO FACES. For some reason I have to get them facing the right way with this method.....After all that, everything is quad and nice....Still, after the conversion, the damn thing tears apart....My geometry is perfect in Poly mode, but once i go into SUBD.....YUCH!!!!!!

Any IDEAS how to prepare the model for a better SUBD conversion?

[drblacksnake]

well.. best thing I could suggest is to do some subD models form scratch yourself to taste algorythm of conversion. Keep them all 0-level (they should look something like second sphere posted by Joojaa). Also quad faces is only half of the deal, since edge topololgy is of same importance.
But this is only poly2subd thing, where everything (at least for me) is predicatble. Pain begins when I try to do conversion of 0-level subD to NURBS.. at least I've tried few times just for curiosity, and came to conclusion to beter do not, since I got bunch of NURBS patches with incontinuous isoparms and strangely distributed seams. much better is to convert to beziers - this gives clean model, just I'm not sure about maths behind and how much Maya loves them.
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Each square in bezier model is a separate patch - 1 subdFace = 4 bezier patches. I have no idea why don't guys from Alias couldn't make these things 4 times lighter - I hope M7 offers more sane method of conversion, since nowdays I should do manual blending of all those patches. wishlist, huh?

[joojaa]

the second sphere posted is actualy a nurbs surface thets been reduced from the extra tangency at the cost of a bit of accuracy, but without loosing the tangencyy of the patches themselves. but your rigt beziers more closely describe the shape. But mathiematicaly they are just special cases of nurbs thats why the bezier conversion option is under the nurbs conversion. choise is more patches versus unevenly distributed points.

se what i did is actualy veruy close to the bezier one but with 4 times larger pach dividions. but yeah id agree going thet way around and then attaching might be a saner and cleaner solution

[joojaa]

And oh just to pointt out each face becomes 1 bezier patch BUT noote that teh underllying pole killing algorithm of the subd actualy makes more levels that your original modell has to comensate for poles.

But aparently form your post never for plain level 0 surfaces. So trying to keep 1 as the true target level would be the thing here??? chekked this, and yes true. So the thing is you want to use pulys that are of level 1 thatway each apparent face tiurns into on patch. Now the reason maya does this is a bit wierd.

this hearachial splicing is something that most find odd because only realy maya and zbrush (wierd enough on maya side this is complained about when on the zbrush side its the msot rejoysed part of the prg, go figure) has this. Its actualy a pretty smart move, because thisway you can modify the offending interpolation thats inevitable ith your poled modell.

[joojaa]

yes its definetly wierd if i take the dodecahedron collapse it 2 times to get a all 0 level object THEN maya generates 4 times the points to compared to me conevring the noncollapsed subd. THis must be a bug/ oeversight of somekind?! could actualy ask alias to fix this.

[drblacksnake]

if this hierarchy thing was adressed to me, then it is ok since all my subD models are 0-level so they folow poly edge topology.
in the picture above I just showed real, not geo-primitive sample of what crap happens when doing conversion to Nurbs (look near armpit, groin and ear).
bezier output is definately better and I don care about "less precision" (on the last resort we are doing animation, not scientific modeling like in Studio), just there could be 1/4 of current number of patches, and this I reject to understand as be right, because when doing surface attachment for each of those 4-patch-set, then they become to precise and clean pieces and fit into previous curvature perfectly.
ok.. I do not use this conversion at all because it is not spent time worth.

P.S. and about that 2nd sphere - Yes, i knew its NURBS, but in my prev post it was stated "looks like" meaning CLEAN and without that ugly number of isoparms or non-0-level appearance like in first image in this thread.

[joojaa]

bezier isnt less precice its as precice as the nurbs patch conversion. Just more individual patches tahts all. Also I think you missundertood a secondnd thing about my drift. MY simpler vesion was done in a totaly different way from bezier conversion, its a standard nurbs conversion like the one on left but rebuilt after the conversion to contain less spans (the fact thet the result looks the same does not mean it is it incidentaly also creates one face per 4 target resolution faces as opposed to bezierr taht has following problems). giving you a total of 4 different objects all looking the prettymuch same here on my 3 last posts, andm mathematicaly 3 of them are identical.

Anyway ive noted 2 possible bugs about bezier conevrsion!

1) if you convert a subd wich is totaly 0 level, then you end up with a conevfrsion taht corresponds to a level 1 surface.. for some reason.

2) if you convert something that has more than 0 levels it conevrst at the precicion of the lowest one, wihc each of the connvertees lowest faces corresponding to one face. So that means you get lighter modells uppon conversion of models that are not collapsed and do contain levels (asuming you could go thatwya offcourse you shoudl tryu to ainm at sufaces with 2 levels as the conevrsion makes for LESS faces! asuming they convey the same data)

BUT this too contains a slight bug it creates each face 2 times on top of eachoter.

heres a picture: the lighter modell is the one directly conevrtted for same the platonic solid, and the denser form the same solid, but ist collapsed so that it only contains level 0 transforms. They should definetly be exactly the same!

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click to enlarge

And yeah same holds true to realworld meshes tough its actualy hard to target level 1 as opposed to level 0. and since you cant realy move backwards in teh pursuit very easily its not a desirabl result.

Conclusion, maya reacts to models as if they ware 1 level deepar than they are if the level 1 isnt in use maya still internaly seems to think it is. This actualy thet working on just level 0 modells is no better from amyas point of view than 0 and 1 level ones.

So theres definetly a bug somewhere in the process. or then something totaly funny is going on on my test machine, i must test this on older matyas too.

PS its important to note that mathemathicaly BOTH of the patched ones are precicely as accurately the same.

[drblacksnake]

ok, thats good to hear about precision, but You have mentioned You've rebuilding done - how it relates to my model which after conversion to nurbs consist of randomly distributed seams between patches? at least I couldn't find any automated rebuilding option and that way it sounds like individual approach to each patch what makes me sad. i catch myself to be repetative, but much more reasonable is to sew togeter each of those 4 beziers - this at least wouldn't require intellectual tension.
I just hope Maya ocassionally dont interpret 1-level subd as 2-level one, and so on
ok, thanks, Joo!

[vivaldi0]

QUOTE(drBlacksnake @ 09/05/05, 12:47 PM)
Each square in bezier model is a separate patch - 1 subdFace = 4 bezier patches. I have no idea why don't guys from Alias couldn't make these things 4 times lighter - I hope M7 offers more sane method of conversion, since nowdays I should do manual blending of all those patches. wishlist, huh?
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As for Maya7.....no it is still the same conversion, but there is paintFX to NURBS and PaintFX to POLYS, and texture to Geometry conversions.....Looks like they are going in a different direction with conversion features. Maybe by Maya 8 there will be the Poly to NURBS, or at least the a slider to adjust the surface parametrization.

The SuBD of the FETUS looks really nice. I have been trying to get to that level, but with no luck. I would be happy with the SUBD to Bezier, but again...the SubD alway has crappy topology. Trying to get there with minimal edge editing is tough.

I wonder if I took the original mesh into Zbrush and then converted the mesh there. Would Zbrush give me better topology???

[joojaa]

No poles will still be poles. the end result is the sae because the algorithm is allmost identical.

what do you mean by aslider to adjust surface parametrisation?

[joojaa]

oh and PS. i dont think youve understud what the conversion tools are mainly about i mean the clear point with most of theese tools is tha tyou can take the maya properitary implementations and export it to any renderer in a format that they most likely will undertsand and eat. atkeast the following convertters fall clearly into this category:

nurbs to polygons
subdiv to polygons
subdiv to nurbs
paint effects to polygons (so you can get refrections in mr for example)
painteffects to nurbs
paint effects to curves
fluid to polygons

Thr purpose is to conevrt the data as is, so thet another app without much knowlege of maya way can be used in conjunction. IT does not mean they cant be used for other stuff but thet appears to be their primary function. Now theres certain kind of thinking of primitive unity, but i think they have taken it as far as possible

for example a sudiv to nurbs coneversion whare you can limit the number of spans is not realy psossible because it would sacrafice accuracy. Unless someone comes up with new mathematics suddenly. That is they would no longer be tangent wich would meka the end result a jumble.

And on the oetherhand they are not rebuild tools like surface the surface filtting tools by headus work a bit differently they let you decide how to lay out patches independently of what the underlying surface is and this allowing for much more parctical solutions, but also you decideing how and whare you want to sacarafice accurafy as needed.

Thet said i do think alias IS working on this, but wether we will se it in maya bundle is another thing, as this sort of stuff is far more likely to be part of studio tools instead of maya.