Nurbs & revit ?

[pomalt13]

Hi!

i'm really sorry for the dumb question but:

Are the current massing tool using nurbs ? if no how could a nurbs modeling tool be better than the "other classical" modeling (polygonal)...etc...as i'm reading a lot of requests for the nurbs implentation in revit ( and other softwares)

thanks in advance

[rkitect]

The closest you are going to get to NURBS in revit is in the conceptual massing tool (available in 2010 or higher). You can create lofts and what not but from my understanding you will still end up with a subdivided (sub'd) polygon geometry. Here are some pages that I hope will help clarify for you. (http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=nurbs+vesus+polygon)

Basically as of now NURB vs Polygon is preference, most modelers still lean towards sub'd poly modeling as opposed to NURBS and when needed some will start in NURBS and then convert to poly.

[Scott D Davis]

AutoCAD 2011 will model in NURBS and then convert to Solids (yes, solids!) that can then be used in Revit with the Building Maker tools (Wall by Face, Mass Floors, etc.)

Great new modeling tools in AutoCAD! Yeah, I know.....why AutoCAD and not Revit? All I can say is be patient!

[AP23]

Rhino and Maya are more suited for nurbs modeling, so I wouldn't recommend Autocad 2011 unless you don't have access any other choice. Revit can create some basic solids and surfaces, but their not build up of nurbs and polygons, which is why there are many limitations within the software yet. Many firms use both nurbs and polygons to build models as its still the easiest, fastest and limitless way of modeling.

[pomalt13]

Thanks every one !

So revit is not using nurbs nor polygonal modeling, is it creating a new way of modeling or just a matter of time till we see Nurbs in Revit ? ( cf. Scott post )...!

[rkitect]

Revit's geometries are polygon based.

[pomalt13]

ok rkitect that's clear now.

if i may ask, why then architects like Zaha Hadid & Gehry are using some nurbs based modeling softwares ? is it related to the construction part or the design part ...?

[rkitect]

They are using nurbs based software because the software they prefer to use uses nurbs calculation methods to create geometry. Some people use pens, some use pencil, some use paint. Ask any cg modeler that deals in both nurbs and polys right now and they will tell you that it's personal preference. Both come with pros and cons.

For video games the output is rendered in polygons (which is why poly count is so big for them) but the will most likely be using combination of nurb and polys to create their work and convert to polys for final product.

For movies the output is straight rendered animation output; the DVD doesn't care if the model was polys or nurbs because it's just still images processed at 26.7 FPS.

For architecture the output is a building, which also does not care about nurbs or polys. Regarding the method of getting there is just what system you are familiar with. Here is another discussion I found about polys versus nurbs which may clear some things up for you: http://forums.cgsociety.org/archive/index.php/t-779001.html

[j_starko]

HLY CRP !!!!!!!!1

this is boggling my mind. Before I read this thread, I had a happy and content level of abstraction as to how 3d objects were formed.

now I'm immersed in Wiki pages

http://en.wikipedia.org/wiki/File:Spline01.gif

and rhino sites

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

and peer questions as I try to get a better handle on NURBS.


I Like learning new things !

Poly's are easier to understand at first than nurbs, but I can see a benefit to things being drawn with nurbs. the biggest distinction from my newly found understanding is that with a Nurb Based object, you would have a surface that is actually curved.. where as with a poly based object, the curve is made up with hundreds, millions or possibly billions of segmented lines... Is this correct ?

[rkitect]

That is exactly correct. It's like the difference between Raster and Vector Graphics, but with a third dimension added :)

The nice thing about NURBS and why it would be great is the mathematic nature. The parametric nature of Revit is very inviting to the parametric nature of NURBS. I'll make an example video in a second to demo one of the big benefits of NURBS modeling in Revit (which is also a big disadvantage!). Just need to switch computers.

Check this Video: http://screencast.com/t/ZjViNDRhOWM

You can see that the geometry outline is vector based, you get a smooth curved radius, however the geometry itself is based on polygons and that when you get sufficiently small with geometries in revit it can no longer break polygons down to a small enough size. This is probably where a lot of the "Line too small" errors come from as I'm betting the polygon size is based on a 1/32" unit (the same unit that you can not be smaller than in a single object length.

The advantage of having NURBS would be that this would be a perfectly smooth sphere in solid geomtry.

The disadvantage is that you would be able to model at nearly infinitely small scales... can you say OCD nightmare?

[j_starko]

that was a great explanation and demonstration , thanks !

[j_starko]

funny timing with this thread,
i was just modifying a sink component, and was trying to show the drainage holes in the bottom of the basin. if I make the holes the correct size ( too small for revit ) it makes them looke like little hexagons. if I exagerate them and make them bigger there's more segments and it looks more accurate.

I feel like such a nurb nerd for noticing this now !

[AP23]

Most clients will notice that and ask why the hole is segmented or why the railing profile is not round. Then you got to go through the embarrassing process of blaming Revit , which they don't buy.

[twiceroadsfool]

Most clients will notice that and ask why the hole is segmented or why the railing profile is not round. Then you got to go through the embarrassing process of blaming Revit , which they don't buy.

LOL. MOST? In 5 years ive never had a client ask. Nor have i ever had a client get a hexagonal railing. MOST. LOL.

(I know, i know. No one in the US does real architecture, remember?)

[cliff collins]

I have to ask a simple question here:

Has anyone in this thread actually ever had a NURBS surface-generated form
BUILT in the real world?

If so, what was the workflow? i.e. Rhino>Revit>Max>SAT>CNC etc.....

From what experience I have, the forms can be extremely expensive to build,
and I've seen quite a few of them get "VE"'d out once bids came in.

cheers..

[rkitect]

Has anyone in this thread actually ever had a NURBS surface-generated form BUILT in the real world?

Just to clarify, I'm assuming you mean a complex NURBS form. NURBS is not the final outcome, but the means of making it. A complex Polygonal form would be as expensive to build as a complex NURBS form. The only difference is that the NURBS surface is formed via mathematics and the Poly surface is formed by millions of tiny triangles (if it was done right)

[cliff collins]

Carl,

Yes-I understand the poly / NURBS technical differences.

The question is more to the point of HOW a compound curve ( call it whatever you want )
gets built--workflow from modeling thru to the built product.

cheers

[rkitect]

Once upon a item there was an excellent article from the guys that built the Three Ring Office environment on how they went from design to build. I will dig around and see if I can remember where that sucker is. Until then enjoy the final product: http://www.wired.com/culture/design/multimedia/2007/06/gallery_nemo_office

[cliff collins]

Interesting........

but I don't see any NURBS surfaces.

cheers

[rkitect]

What makes you say that? There's no way to tell from the final outcome if a shape was created using NURBS or Polygons, unless the original CG artist is standing there and telling you "I used NURBS for this form."

[cliff collins]

Carl,

It just looks like everything in that space is a flat extrusion--I dont see any
complex/compound curves, ( except maybe the lamp shades) like the attached.

just sayin......

cheers

[rkitect]

NURBS != Complex Compound curves. Download a trial of maya, select your NURBS shapes and note that extrusions is still an option.

The shape that you posted in the image can be made from polygonal geometry just as easily as it can from NURBS.

[cliff collins]

Agreed.

movin' on.

cheers

[rkitect]

I was never able to find that article, but from what I recall they took the geometry and used some unfolding software, similar to what you see people using to make those paper models (ie: http://cp.c-ij.com/en/contents/3157/chipmunk/index.html) to create as many flat surfaces as could be used. Sent those flat surfaces through a CNC mill to produce the pieces for assembly and whatever else they needed that was too complex for simple flat surfaces went through a CNC on a different stock. Each piece had an assembly number milled into it (or marked after wards) to help assembly on site. I really wish I could remember the site for the firm that I saw the process on.

[jeffh]

The project was done by Jeffrey McGrew's (long time poster here but have not seen him for some time now?) firm. It was done in Revit (probably 3 or 4 years ago) so I know NURBS surfaces were not used int he process. I don't recall exactly how they transferred info/geometry from Revit to the CNC machine. Here is a link to his firms website. You might be able to dig up some details on the precess there.

http://www.becausewecan.org/

[AP23]

NURBS != Complex Compound curves. Download a trial of maya, select your NURBS shapes and note that extrusions is still an option.

The shape that you posted in the image can be made from polygonal geometry just as easily as it can from NURBS.

True, however common sense will tell you that curtain buildings (Zaha Hadid projects for instance) were made through the usage of NURBS or polygons. Is the same as assuming that a swimming pool is dug with an excavator instead of a spoon, while both will get the job done.

That said, looking at the World Expo, it's save to say that most of the building where modeled using nurbs or polygons.