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STEP conversion fails on most of my SiemensNX data

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Gabriel Sumner:
Hi everybody!

I thought I'll post my latest tests in a new thread, to start of fresh. Yet pickin' up our discussion here:
https://forum.corona-renderer.com/index.php/topic,7538.0.html

Over the last two month I have been dealing a lot with new CAD data provided by the client, i struggled day and night and tried a bunch of the major CAD translation packages out there (well, DeltaGen is yet to be tested ;).

To be more specific:
- Maya
- 3dsMax directConnect
- 3dsMax nPower Translators
- VRED Pro
- Showcase
- SAP Visual Author
- Transmagic (to check for any CAD file problems)

The original data was provided through SiemensNX. I yet have to ask for any kind of polygonal data format (like JT) to be provided directly. This way I will be able to test wether tesselating the modell natively without STEP conversion yields any better results...
I can confirm what Ondrej said before: the tiny triangles are the issue. After importing STEP as a rough mesh some of the areas cleaned up. Yet this is not an option for hiRes obviously.

Besides of that I tried using 3DCoat and Mudbox to retopologize the data into quads without luck. There is a new paper for a nurbsToQuad workflow, but it has to be implemented by someone:
http://www.sciencedirect.com/science/article/pii/S0167839614000624
In the screenshots I have collected some results of my testing. You can clearly see that Maya produced clean "unbroken" mesh in places, where there was a solid Nurbs > Quad Mesh conversion. To clean up all the surfaces Maya produces would still somehow defeat the purpose - i do require a simple translator solution for everyday work.





The errors are highly resolution dependent - you might not see the black lines appear on low res, but since most of us are doing high res in production...
I merely wanted to point out the problems I've been having with CAD data for the last two month, I understand that Ondrej is working hard on many different things.
Nevertheless to my mind CAD data conversion / translation / teselation (call it whatever you want ;) ) shouldn't be last priority. I believe there are a lot of people out there like me willing to use Corona for any type of industrial viz.
As for me, unfortunately up till now I had to stop using Corona for CAD - every model turns out to be a pig in a bag. The only option left is to do clay rendering turntables over night (or days!) just to see if any broken normals appear.

Paul Jones:
Have you tried another renderer in max?

lacilaci:
hi, I don't know 3Dcoat and had bad experiences with mudbox and how it handles geometry in past (loong ago..)

But, you should be able to do it in zbrush. Making the whole cad model a high density dynamesh and then retopo.. I've done it in past and it was working just fine, however those meshes weren't really that bad...

Anyway, zbrush might be worth to try once you have the polygonal mesh

I often work with some cad stuff.. So maybe if you would provide some "worst case scenario" cad model I might take a look on how to make things work.

Gabriel Sumner:
Thanks to everybody for replies!

@ Paul Jones: i didn't provide a comparison here, but I have used Vray and the Showcase renderering engine. Both provide much cleaner results (no ugly small triangles), the only places where there were problems in Vray were due to problems in STEP file itself, after rebuilding it in Moments of Inspiration there were no problems. So Showcase and Vray saved my day...

@lacilaci: I would gladly provide you with data, unfortunately everything is under a strict NDA, i am still strugllin' to get at least so parts for public use. Thanks for the tip with zBrush, I'll give it a try as soon as i have a bit more free time.

PS: Rhino conversion yields best results so far, but is not an option - our company is not buying yet another piece of software, after having spent a lot of money for nPower plugins.

Thanks and CheerZ!
G.S.

pokoy:
Not sure if you tried this, but in both nPower NURBS objects and Body objects, there's an Edge Length parameter that will help to avoid long thin faces, see attached images.

Also, not sure what max version you're on, but in max 2015 there are some severe issues with importing NURBS data where the sewing tolerance is way too low and results in open edges, while in max 2016 the same geometry imports as volumes and is water tight.

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