[deadalvs]

hi there !

take a look here:
http://cgdominance.com/forum/viewthread ... ad_id=1045

i have a hard time to get into the understanding how the subdivision (breaking up in separate parts) of nurbs surfaces can be achieved best. how can the creases be modeled the most efficient ?

by modeling the part directly as a trimmed surface or by building a whole chassis and break it apart ?

and most important: how ( the hell ... ) can these gaps between the surfaces be modeled with a constant distance ?

yes, i am using maya and i know this is not the optimal piece software for such tasks at all... i'm just curious about the methodolology behind it.

thankful for any input !

[dilbert]

Without a doubt, the best way to model a car with a NURBS based software is to model the entire body as a flowing continuous surface, and then break the panels into segments and tweak as necessary. The subdivision is usually done by projecting an offset curve onto the surface at the divide point, and then triming the result. Some softwares have an automated command for this (e.g. Autodesk/Alias Studio Tools has a tubular offset command that makes life really easy), but often you have to do things maunally.

Here are two good books/DVD's that will give you the basic techniques:

http://www.thegnomonworkshop.com/dvds/mod03.html

http://www.amazon.com/Learning-Design-A ... 318&sr=1-1

[ricardo]

Have a look at TSplines, they have a Maya plugin.

www.tsplines.com

Ricardo

[deadalvs]

thx for the replies...

i tried some more with maya and it's REALLY frustrating.

crippled shells all the time. i really like perfect shapes and curvature/tangency, but using maya for these tasks gives just a feeling of trying to fake and hide unwanted parts...

* * *

how long would it take in studio to model a car like this ?
http://www.youtube.com/watch?v=j-rj2bGLWuA

[dilbert]

how long would it take in studio to model a car like this ?
http://www.youtube.com/watch?v=j-rj2bGLWuA

That depends on the end-goal. Alias Studio Tools has the ability to produce perfect Class-A surfaces for manufacture, but that can take a long time to get each edge seam with curvature continuity within acceptable tolerances. However, if you're wanting to render the car for visualization work, the human eye won't pick up the difference between a tangent seam and a Class-A curvature continuous seam, so you can actually model and render very quickly once you know how to use all the tools.

It's just like when you first start to learn how to poly model, and you have to learn all the techniques and hotkeys to create a quick, efficient workflow. I guarantee that if you take the time to learn how to model effectively with NURBS, you will never use polys again for hard surface modeling. They are hugely faster, and much more accurate as there is no "smoothing" algorithm to create a smooth surface.

Here's a link to my gallery. On one of the images, you can see a wireframe of a BMW Z4 that I modeled in Studio Tools, which will show you how I divided up the surfaces for modeling. These surfaces were all curvature continuous, and the model took a couple of weeks. There's also another link to a quick test render I did in Maxwell.

http://www.maxwellrender.com/forum/view ... highlight=

http://www.maxwellrender.com/forum/view ... hlight=bmw

[codygo]

Rhino has tools to check G0-G2 continuity, which are really first and second derivatives of the curves or surfaces, but you can still achieve these qualities without special software If you take care to create lean surfaces with clean cv rows, which you should be doing in autostudio anyways.

G0 is positional, you can achieve this by simply matching cv's point by point at a surface or curve seam.

G1 is tangency, you can do this by creating a line from connecting cv's to a perpendicular cv that is already in a position you want to keep it in, then copying that line tip to opposite tip, and moving a matching cv on the surface you want to make tangent along that line, sliding them anywhere on that line changes the magnitude of the tangency. Repeat for all boundary cv's.

G2 is trickier, and really requires that you look at curvature combs, but you can do the same trick as with G1, instead matching 2 extra cvs, but the results will usually not be ideal except across most automotive yz planes where you want near flat but smooth transitions.

You can use zebra stripes or curvature combs aside from the tools that automatically try to arrange the cv's into G2 connections.

Another key thing about surfacing is using parent surfaces and thinking of features as discrete surfaces. For example, a car can have some large single, simple surface for its sides from front bumper to rear bumper, and the creases would be intersecting surfaces which are filleted some amount. Wheel arches are separate surfaces and are then intersected with the sides.

[deadalvs]

hmm... let me think about these inputs a little...

* * *

a question ...

(i guess renderman's the only true nurbs renderer around that does not need poly tesselation to work, is that true ?)

imagine a nurbs sphere modeled in separate patches. now for every patch, the render-tesselation in U and V texture space can be defined. let's say every patch but one have a 30x30 tesselation and that last one has a 25x25 tesselation. that would result in edges being broken when rendering. if that object is lit from inside, this would be visible in close-up renderings.

now. if i have class A patches... is it guaranteed that no such breaks happen when i want to export and render in maya / maxwell ?

can studio export in .igs or another nurbs-compatible format or does it use some studio-unique types of nurbs shells/patches that cannot be exported traditionally. like for example when three fillets come together and have to blend smoothly ?

or would the export be «perfect» when using polys ?

* * *

could someone post a small poly model to see how a «class A» seam between two pieces looks after export ?

[dilbert]

I think you're basing your evaluation of NURBs rendering from Maya, which is a bad example. I also have Maya, and used it for years when I first got into this field. Maya has a decent set of NURBs tools, but there's practically no evaluation/editing ability in Maya to ensure that you have actual continuity between your patches. Also, the tesselation system within Maya converting NURB's to polys at render time pretty much sucks.

The higher-end software such as Rhino, Solidworks, Studio Tools etc., do a much better job of exporting files into a renderable format such as OBJ files. Take a look at my previous post with the links to the BMW Z4 model. I exported that model from Studio Tools into Rhino in an IGES format, and rendered it with the Rhino plugin for Maxwell. You can see from the render that there are no visible breaks in the seams between patches. Maya is great for poly/animation stuff, but you'll not find a single product design, engineering, manufacturing etc. company who uses Maya in their workflow.

All the major "NURBs" or Solid modeling software will export/import in just about every format there is to include OBJ, IGES, STEP, VRML, etc.

[deadalvs]

and ... what titles (books, dvds, ...) would you guys recommend to learn studio ?



* * *

about rhino ...

i know rhino has some neat tools and is very stable (even programmable / scriptable). but i think when i really have to learn a new software, i'd personally go rather for the most mature one directly. just to be sure i miss no tools «ever».

[dilbert]

Well, unfortunately Studio Tools is not very well documented with books/dvd's. It does have a limited community website linked through the main autodesk website which has some great tutorials. Here's some:

http://www.amazon.com/Learning-Design-A ... 947&sr=1-1

http://www.thegnomonworkshop.com/dvds/hgo01.html

http://www.thegnomonworkshop.com/dvds/dbr01.html

Here's the links to the Studio Tools websites:

http://usa.autodesk.com/adsk/servlet/in ... eID=123112

http://aliasdesign.autodesk.com/

http://aliasdesign.autodesk.com/learnin ... ge[1555]=1

Here's an article that talks exactly about Auto surfacing in Studio Tools:

http://aliasdesign.autodesk.com/learnin ... 01_133097/

Also, think about what your end goal is. Studio Tools is used heavily in the Auto industry, but not much in the manufacturing industry. Solidworks, PRO/E, and Unigraphics are used heavily in Product design/Industrial Design Engineering, and Rhino is starting to be used more, but it still has a long way to go in the actual job market. They all just about do the same thing, but in different ways. Like I said before though, all will export in every format known to man, and some are interoperable. For instance, Solidworks will open a native Rhino file and vice versa.

Also, you have to consider price. Autostudio will run you around $25,000 (although you can get the full personal learning edition for free to gain the skills without paying a penny), Solidworks around $3500, and Rhino just shy of $1000. That's a big spread.

[PA3K]

... they were using ICEM Surf in the automotive company I was working for. And every other small supplyer - companies were using it for final surface modelling... but I really didn`t like interface (GUI) ... maybe it is some kind of professionalism if the graphic interface look bad (just my opinion) ... they also told me, that it is not NURBS modeller, but Bezier (not sure)

personaly I like Rhinoceros, I am modelling surfaces with some kind of continuity exactly the same way as CODYGO described - control points on - line from end point to first next control point - copy this line from control point to end point - and first control point of other curve or surface should be on that line - so curves or surfaces have the same tangent at the end ...

and the last thing is method of creating surfaces ... i also think, that making one general surface and than trimming is better, than making surface from many single parts, but I found that trimmed surfaces has fewer editing commands usable...

[ricardo]

about rhino ...

i know rhino has some neat tools and is very stable (even programmable / scriptable). but i think when i really have to learn a new software, i'd personally go rather for the most mature one directly. just to be sure i miss no tools «ever».

You will learn the witchcraft of NURBS modelling what ever the toolset you pick. All of them adhere to the same principles, the difference is in how you get to a desired result.

I don't know all there is available, but I have tried studio briefly and use rhino on a day to day basis.

Knowing maya as far as I remember will be no use on learning Studio. Studio use the old power animator interface (still does, righ?), and the jump from Power Animator to Maya was disruptive.

I first used Rhino when I was a Maya user, and just gave up NURBS modelling in Maya immediately. It's damn easy and strigh forward to use. Not to mention the 10 fold price difference.

[deadalvs]

well.. i'll give maya another go tomorrow.

i ordered a book on studio so i can dig a little deeper. i'll certainly learn something in there for overall-knowledge.

based on the price-range... 25K $ really seems to be an incredible lot of money, but it's no wonder when you get the tools i've seen in the tutorials so far.

* * *

i'll let ya know... thanks so far !!

[deadalvs]

okay.

here's my first approach.

we were give side and top blueprints of a mercedes and had to create a «speedform» by revolving a curve and then tweak the hulls and cvs until the form is approximately met.




next step was just modeling the rest off this surface as a first exercise ...

[deadalvs]

looks not like a mercedes... more like a stock-car-porsche ...