I import the file to blender and it works fine but is very unsmooth
Then I use “set smooth” and Catmull Clark subsurface to smooth the .obj file
but the result is still rather bad.
This problem happens usually with complex surfaces which are not trivial to export/import.
Well…Maya can import those files succesfully. I just import the NURBS Rhino file to Maya as polygonal .obj conversion and result is smooth without any tricks. All to easy.
Why I fail with Blender? Should I have some plug in so that the NURBS to .obj import from Rhino works nicely? Many software can actually render NURBS files which are converted to polygon form like .obj form.
Please help cos if I could render and unwrap .obj converted NURBS files in Blender I could do very cheaply lots of things, like animate Rhino files. I think there are other people with this problem also.
OZON, unfortunately, NURBS development in blender is slow (altho it is ongoing, AFAIK.) Hopefully, one day it will allow the import of OpenNURBS native data…
but for now, we have to deal with “tweaking” our imported & converted-to-mesh models. A couple of things you can try: be sure that all “doubles” are removed. In my experience with importing CAD models, the mesh, once inside blender, seems to have duplicate vertices/faces for all the surfaces. Removing Doubles (w-key menu) helps clean things up.
Next, its always good to ctrl-n “Recalculate Normals Outside” just to be sure. Then, if you intend to use subsurf, you’ll likely want to try to convert your meshes from tris to quads (alt-J in editmode). This is rarely a perfect operation, usually very messy on cylindrical models (@ the ends… and fillets? fugeddaboudit!)
Finally, in addition to “set smooth” (which usually messes up their viewport display in blender’s OpenGL implementation) you’ll be wise to enable “Autosmooth” which helps iron things out at render time (won’t help with their viewport display, take note.)
Beyond these beginning steps, cleaning up an imported mesh can mean manually “fixing” the bad topology. Unfortunately, this is just the nature of the beast for mesh modeling.
Your advices work but I have tried all of them. However it is a relief to notice that I am trying something which is not possible at all. Now I do not need to ponder this anymore.
However there is one trick which works, but it is a compromize tric but I use it while I make things with T-Splines.
Make a nurbs surface in Rhino
Do not trim it, it will be ignored.
Use Rhino’s “from NURBS control polygon” feature under “Mesh” tools.
Now export this as obj to Blender…
Then in blender “Add modifier” and then “subdive” surface with catmull clark and then “Set Smooth”
Voila it is almost the same surface as it was in NURBS…not 100% but 99% and this is enough cos its smooth then good enogh for manufacturing.
Export as obj back to Rhino…you may use or use not subsurf smooth depending the accuracy level you need…
Convert to T-Splines then to NURBS…
When it is in NURBS then trim it…
Voila you have trimmed polygon surface…
This is how I make things with Blender and Rhino and T-Slpines…it works 100%
OZON, interesting workflow. If I may ask, why are you needing to make the transfer btwn Rhino and Blender here? Is Blender able to perform a function that Rhino is incapable of? Or are the mesh modeling tools in Blender easier to work with?
…just wondering to be enlightened. I’m not a Rhino user and don’t deal directly with editing NURBS surfaces very often (I’m on CATIA V5 in an industry that only rarely requires direct surface manipulation.) Thanks!
Yes I use Blender as polygon tool cos its simply the best to make quick polygon modelings. I dont like Maya or Max cos they have no decent shortcuts like Blender. Blender is a professionals tool, made for a true heavyuser in my opinion. Maya and Max have both heavy user interfaces which are a bit clumsy after all. But I want to point that this is my personal opinion, I like Blender more than Maya or Max. It brakes my heart that people has not done that open nurbs system for Blender. If there was a good import for NURBS and some tools to convert them to polys like I described Blender could be a true killer software. I honestly think like this.
