converting cad models with polytrans or accutrans

I’ve been working to import several large cad models (SolidWorks) into Blender via STL format. The result is not pretty. THough I"ve tried the “delete doubles” and “tri’s to quads” tools, the geometry is still a topology nightmare. I discovered Polytrans and Accutrans 3d and I’m going to jump into the demo versions of those tomorrow to see if I can get better results. I’ll post something about it then.

In the mean time, does anyone have any other suggestions about how to get clean geometry when converting from cad programs to Blender?
Maybe there’s some software, or a workflow or method or tutorial that I’ve never seen? Any opinions on the merits of polytrans vs accutrans 3d?

Thanks.

So… Obviously a lot of people on this forum are well aware of Polytrans and Accutrans 3d and I’ve seen a few threads about it, but I didn’t find much discussion about the merits of the software or how it solves problems of porting geometry, animation data, and materials between platforms, which is why I started this thread.

First, I found this document which is a pretty good overview of very many of the file types we run into and the purpose and merits of each:

Also I thought someone might benefit from some of the answers I goy from the Polytrans guy. If you’re trying to convert CAD based geometry into something usable by Blender, this might be interesting to you:
It has my questions & his answers.

>I have a few, very large assemblies in Solidworks that I’d like to work
>with in Blender (the open source modeling/animation software).

Yes, almost every bi-hourly sale I’ve made for the last 18 years is for SolidWorks. I provide the main SolidWorks conversion system for the entire 3D world. Hence, I and my staff know it very well.

> Blender can import .obj or .STL, and I"ve exported the files to STL,
>but when I import them into Blender the model topology is pretty bad.

That is because STL is the world’s worst file format which exists. Nothing could be worse. STL was made in 1995 as a quick hack to convey data to a Stereo Lithography machine. It just contains one large glob of triangles and nothing else. It does not contain the all-important vertex normal data, object definitions, assembly hierarchy, materials, etc. etc. I would never have anyone use STL for conversions.

>Almost everything is triangles

That is something which confuses non-CAD people. Since NURBS were first invented in the 1980’s, all MCAD programs always tessellate to triangles and never quads. Quads cannot capture the curvature of a NURBS surface. Quads are only used in non-CAD software such as zBrush and Cinema-4D.

>and Blender does have a tool that tries to convert triangles to quads,
>but it only kind of works.

One cannot “convert” an arbitrary triangle mesh to a uv-aligned quad mesh as non-CAD envision. Programs like zBrush are procedural, non-NURBS, non-CAD programs which create simplified quad-aligned meshes but that never occurs in CAD. In CAD, the tesselaltors are made to create very thin, small and narrow triangles since that is the norm.

>This, as you probably know, creates
>models that are difficult to edit, have bad shading
> I can fix it, but often it would be just as fast to redo the
>model from scratch.

  1. The bad shading is due to the usage of STL files.

  2. “Difficult to edit” is because you are using a non-CAD program to edit CAD tessellated data. This is all very normal and the standard practice used by all companies since the 1980s.

>So… Does Polytrans deal with this? WIll I be able to edit, texture,
>animate models that were exported from SolidWorks.

What you wish to do is purchased 6 times on average every day for 18 years.
So, yes, all of my customers purchase the software to do exactly as you desire. However, I never sell to any Blender users since they usually want free software while my SolidWorks solution costs US$640 to US$790 on average.
You will be able to achieve these same results:

The following are images created by relevant customers, similar to yourself and your conversion requirements:

  http://www.okino.com/mainpic13.htm
  http://www.okino.com/mainpic12.htm
  http://www.okino.com/mainpic11.htm
  http://www.okino.com/mainpic.htm

Now, another common misconception is about texture mapping. No CAD data from SolidWorks will ever have any uv texture coordinates or texture mapping information associated with it (because SolidWorks Corp. does not like Okino transferring their data to programs like Blender). What you must do is use a uv unwrapping program to flatten the mesh then assign new uv coordinates.

You will also want to use the VRML2 or FBX file format to convey the data into SolidWorks from the Okino software and not use STL.

Regards,

>Also he said this:
What you’ll find around the world, is people trying to use 3ds, OBJ, STL and DXF to attempt to convert their data files. All of these are the 4 worst file formats which exist, yet you just can’t tell that to people that don’t understand the history of these 1980s file formats. I recommend you look in the “Best Practices” section of this page:
http://www.okino.com/solutions/c4d.htm

I found it educational, hopefully someone else can benefit from these answers.

Very true, STL is a nightmare. I just finished a project where I received a very large STEP File created in solidWorks. I converted it to STL in FreeCAD and imported it to blender. Everything was glued together in one large Object. Fortunately you can separate in blender by linked geometry, but the process took 16 hours on my Quadcore i7…
Then came the sorting, grouping, normal fixing, etc. The result looks okay, but a converter like the ones you mentioned would have saved me a lot of time.

Thanks Ikari. I’m going to look at MOI.

I have the same problems, we use Blender at work in one special scenario, to render out CAD models. Using STL export/import. The meshes are a mess, the shading is completely off, with artifacts, etc. With a lot of work, subsurfing, etc. the results are useable.
However, the real solution would be a good NURBS system, that has been missing from Blender for many years.

One of the GSoC projects this year was NURBS Modernization (http://wiki.blender.org/index.php/User:Jjoonathan/NURBS_Final_Report), which really got my hopes up, it looked very promising. One of the goals is to be able to import nurbs file types (including step!). However there seem to be issues with building for Windows, and GSOC is also over, meaning it is now up to the programmer in his own free time to finish it, test it, integrate it into trunk, etc, etc… I hope some programmers out there will help with this. Maybe then one day we actually will be able to import CAD directly into Blender.

Thanks Zsolt. I read the Wiki you linked to and it really helped me understand better the nature of the problem of importing CAD files.

I just ran into this problem the other day. I solved it by using the IGS version of the CAD file. I imported the IGS into FreeCAD and exported an OBJ file. I ended up with a 5.9 million face model. After converting to quads and removing doubles I ended up with around 3.4million faces. A heavy scene, indeed, but still usable on my meager system.

It’s good to hear that FreeCad exports to Obj. Surprisingly SolidWorks does not (at least not in my bare-bones version). I may use this method in the future.

Something else I thought someone reading this thread would be interested in, is this article:
http://www.designworldonline.com/organic-shape-modeling-for-engineers/

It doesn’t really offer any free solutions, but it definitely helped me understand the challenge of linking CAD data (NURBS models) with polymesh/Subdivision-surface models.

Thanks Zsolt for the link to the wiki about a NURBS update for Blender. I read it, and I too hope it happens. It seems to me to be one of the biggest holes in Blender’s pallet of tools.
Not that I’m complaining about Blender. It’s the best free thing I’ve ever even heard of.