STP file Conversion - Nurbs to Polygons

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  03 March 2013
Thumbs up STP file Conversion - Nurbs to Polygons

Hey guys,

I've googled and searched this forum already. It has been discussed but has been very software specific.

I've received an STP file (Step file which I suppose is under CAD) from my client. I am using Maya2012 and it opens just fine in there. Only issue is that it is made from Nurbs.

Seems that nurbs is heavy to handle, and Vray RT doesn't really support it, i'd like to be able to light this using Vray RT.

Is there a way to convert this format into a high poly mesh? Which software- I heard Modo can do this? or which Plugin? Is there a company that does this and should I even be going that direction?

Any information is helpful. Ultimately, I need a polygon file for texturing and control. I tried converting the nurb patches bit by bit and combining them but it doesn't seem to work that well.

Thanks in advance for any advise!
 
  03 March 2013
Complex nurbs are not easy to mesh in a good way. In the process the shading gets messed up pretty often. There are some solutions i know of, but some are quite expensive:

- MOI. Can load stp and write fbx. Meshing is donw at export time. (http://moi3d.com/)
- Rhino3d. Nice nurbs modeling solution. It has a meshing features. (http://www.rhino3d.com/)

I tries MOI with a very simple model (Extruded object with some booleans, chamfers etc.) and a quite complex machine model that seemed to tesselate fine, but crashed in the end because I tesselated too high. Rhino has a 64 bit version if you have a really heavy model.

You're mileage may vary and it depends on your model of course. But I would try these first before going to more expensive stuff. Both packages have test versions.

Happy tesselating.

Cheers
 
  03 March 2013
While I don't use Maya I was under the impression that it could not only mesh native Nurbs but also 3rd-party geometry. What you see on screen in Maya when displaying that model is actually a render-mesh (one can not shade Nurbs, in no application). All you needed to do is extract it. As you are already looking at a mesh I actually wonder why Vray for Maya should have problems to render it.
If the extraction inside Maya really fails, ask your supplier to give you an .obj instead, that's what many Nurbs app can export. Alternatively, as draetsch already suggested download the trial of e.g. Rhino and do the conversion/export to .obj here. But be warned, the mesh topology you get will not match what you might be used to from Maya, so unwrapping and texturing may be challenging.
 
  03 March 2013
Autodesk showcase hands down the best converter I've tested pretty much everything...
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  03 March 2013
I have to disagree concernign Showcase. I have worked with RTT Software before and they have really good tesselators. But you will not get the software easily so that is not an option.
Autodesk has aquired VRED recently. Also a very good solution but expensive. I was going for a simple, more low cost solution as an advice here.
 
  03 March 2013
Moi3D gives you good export options and it works just fine here. You can control tesselation via value input during exporting. We use it on a daily basis in connection with C4D. Should work with Maya as well I guess.

Maybe Autodesk Inventor would be alternative. But Moi3D is just a cool software in general.
 
  03 March 2013
Okino's PolyTrans is my go-to for CAD conversion to workable poly-models. It's not too pricey, and the support is pretty good - even personal.
 
  03 March 2013
Originally Posted by Ice-King: Okino's PolyTrans is my go-to for CAD conversion to workable poly-models. It's not too pricey, and the support is pretty good - even personal.


Agreed on this one.
 
  03 March 2013
Originally Posted by Kabab: Autodesk showcase hands down the best converter I've tested pretty much everything...

I agree Showcase as one of the best tesselator. It will take STP files and depending on how it was setup in the CAD software, it will tesselate and separate the objects trouble free.

Originally Posted by draetsch: I have to disagree concernign Showcase. I have worked with RTT Software before and they have really good tesselators. But you will not get the software easily so that is not an option.
Autodesk has aquired VRED recently. Also a very good solution but expensive. I was going for a simple, more low cost solution as an advice here.

RTT deltagen is alright but Showcase as always give me a better result. I also prefer the way Showcase arrange the polygons over Deltagen.

You can get Showcase for about $800.
The other choice is Poly trans ($395.00). Not the cleanest tesselator, but it does the job.
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  03 March 2013
I have never tried the RTT stuff to be honest but its not really consumer software..

Showcase from my experience handles tessalation across surface patches extremely well which is what most stp converters have problems with..
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  03 March 2013
If STL style mesh is enough for you, you can try FreeCAD (opensource), which can open iges and step files and save it in an STL or similar polygonal format.
 
  03 March 2013
Thing is, i've tried using Nurbs to Polygons conversion. The nature of how nurbs works, it is made out of patches and upon tessellation, the adjoining areas are the issue.

The thing is, vray and Mray render the nurbs just fine, I just need to find a way to tesselate it the way the renders are tessellating before rendering.

I don't mind a high poly count. Was gonna proxy it and I have a Quadro to handle the slow down.
 
  03 March 2013
Originally Posted by Kinematics: Thing is, i've tried using Nurbs to Polygons conversion. The nature of how nurbs works, it is made out of patches and upon tessellation, the adjoining areas are the issue.


There's no Nurbs application which allows for remesh operations with no respect to the underlying patch structure - this afaik is also true for all converter products mentioned in this thread. All you could do is mesh the .step with high settings in any application and then bring the result to Zbrush or 3DCoat.
These apps have remeshing options which are not bound to surface seams, but depending on the original Nurbs topology this process might result in considerably decreased model accuracy. Of course you could also do a manual retopo, then you had full control about the mesh flow.

Last edited by Hoja : 03 March 2013 at 09:37 AM.
 
  03 March 2013
If the model came in a STP file, which application did it originate from? If I can get the client to go back to the vendor to request for another file export, will that work?

Perhaps ask for an obj or something?
 
  03 March 2013
Quote: If I can get the client to go back to the vendor to request for another file export, will that work? Perhaps ask for an obj or something?

That's what I suggested you to do in my first post - why not just read what people write?
But also the .obj will show the underlying Nurbs topology.

Quote: If the model came in a STP file, which application did it originate from?

Step is an exchange format which comes in many dialects. Most Nurbs packages can output them, there's also a few programs which use that format natively.
 
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