Trouble modeling with NURBS in Maya

[zzzrbyte]

This is one of my first projects in Maya, I know the basic tools Maya has to offer but I am not sure my approach to this project is right.

Right now I am trying to model the wheel of a sports car. I built it by creating a CV curve for the wheel's shape and then revolving it to create the basic shape of the wheel's inner metal part (not sure how it's called in English)... See http://www.jurassicpunk.com/temp/basic\_shape.jpg This gave me the basic shape as a NURBS object.

Next, I wanted to create 5 big and 5 small circular recessions in my wheel, so I created NURBS circles and projected them on my NURBS object to create new curves on the NURBS object's surface. I then TRIMmed the NURBS object and had a wheel with 10 holes right where I wanted them.

Now here comes the ugly part... I extruded the 10 holes into the wheel, and then used planar to close them. You can see the result in http://www.jurassicpunk.com/temp/problem\_area.jpg

As you can see, the extruded part doesn't match up with the rest of the wheel... You can literally see the seams in my work... I've heard this is one of the major problems when working with NURBS.

Am I approaching this from the wrong angle? Is there a better way to build the wheel as a polygonal object? Can I solve this problem with NURBS? Any ideas? Any help will be greatly appreciated! Thanks.

P. S. Yes, I do have the detail level of all the NURBS object set to 3, and it still shows in the perspective views and in the renders.

Tal Ater
http://www.jurassicpunk.com/
http://www.childsafetyexperts.com/

[skullnation]

I wouldn't woory about the seams in the open GL view because the accuracy level of the display is rather low in Maya. You can adjust it if you want to but it's not necessary. Try rendering out some images of it with your antialiasing set to intermediate quality or production if you want and your resolution set to ccir 601/quantel ntsc. Before you render go to the rendeer menu (F5) and go to render>set NURBS tesselation>options and bump the stting up to high with the U and V division factor set to 1 or 1.5.

You shouldn't see any seams in the render where it is important. Also if you look at the rim in wireframe mode with the display at 3 you'll be able to see if the surfaces meet properly.

Cheers!

[campbell]

just to add to XanderFX's points.

this is an issue of how trimmed nurbs surfaces are tesselated. to inspect the tesselation of the surfaces, flip on Disp Render Tess flag of their shape nodes (then the viewport ogl is pretty much what-you-see-is-what-you-get). tweak the tess attribs to find a situation where the meeting tesselation across the two surfaces matches enuf to be considered render satisfactory. the res of the trim curve may have impact on the tesselation, tho minimal in your case. edge AAing level is only cleaning up the tesselate edge pixels.

another nurbs based approach is to 'patch model'. no point in me describing it here as there is a wealth of discussion on this in _numerous_ previous threads - just do a search on 'patch' and digest. beiefly tho, this method allows you to explicitly control the tesselation where surfaces meet, overcoming the 'cracks' problem. it'll be easy for you to patch a single seg then radially instance it about your wheel axis.

or you could just use polys that allow you to fuse your pieces together in nearly any fashion you please.

g.luck!

[tim-turner]

There was a great tutorial/discussion, I believe on this site, by Alex Alvarez on tesselating nurbs patches for rendering. Maybe someone out there knows the name and location.
I usually spend several minutes on important seams, with the Display Render Tesellation turned on, tweeking the tesselation settings. Not just the UV numbers, but moving on down the Attribute Editor and turning on Explicit, etc. I have been able to find settings that tesselate the edge heavily but leave large areas like planes rather simple.
The key to getting a seamless seam is to have the tesselation settings break both edges into the same number of polys.

Tim