STL question (mostly about rendering)

[MilesH]

STL question (mostly about rendering)

Do any of you know about an option in the STL spec. that allows multiple parts to be saved in an STL file? I don't mean a non-contiguous singular solid, of course, that's what you get at the moment if you save an Alibre Assembly as an STL file. What I need is the ability to save an Alibre Assembly as an STL whilst retaining the ability to select individual Parts.

 

[mub]

I still don't really understand why you want to be able to select individual parts af a stl file. Of course you can open stl files to have a look at the resulting solid (for example with spectrum) but as far as i know its just a text file which describes the coordinates and loops required for the rapid prototyping machine.
I may be wrong - but that's what i understand regarding stereolitography...

 

[MilesH]

Hi Boris,

I haven't even found a good reference for the specification of it yet...

There is an ASCII version, but I believe STL format describes a triangle based poly model.

It's the only export option Alibre has for creating a poly model. Rendering programs don't usually accept NURBS based formats, so STL is the only option if you want to use an external rendering program with Alibre.

You have 2 options to create an STl :

Export an Assembly - which gives you a singular solid, with all the Parts correctly positioned - no possibility to select a Part, though.

Export each individual Part file separately - in this case you lose the positioning of the Parts which were not created 'in context' within their respective Assemblies.

Hope this makes sense....

 

[mub]

Ah... Ok. That makes sense to me. I've never tried to render something with otrer applications but Autocad and 3ds Max. These applications do it as well with a exported stp files.

Which application do you use for rendering?

 

[MilesH]

I've just started using Maxwell Render. I bought into it at the Alpha stage, over a year ago, but it's only recently been accessible for Alibre (via STL) - workflow's not for the faint of heart, though.......

 

[mub]

:? hmmm...
Correction: They both (at least ACAD) are able to handle sat files, not stp.
Anyway... So i assume that you don't have an Alibre industrial Pack renderer - or do you?
I should get one as my reward for translating while the last user meeting in Zurich. I look very forwart to try it out :mrgreen:

 

[MilesH]

Yes I have the LightWorks Industrial Pack. It works fine, with some limitations.

Just looking for something a bit more photo-real, without the mega learning curve of other top-end render apps.

 

[mub]

I see... I guess it will be difficult to find something what's as handy and cheap and more photoreal.
Just tell me when you found the "real thing".

Best Regards

 

[CGN]

There is a Full (Free to use) version of Shade7LE on the new 3D world magazine,

"Shade 7 designer LE (full)
A full copy of e frontier’s intuitive 3D modelling, rendering and animation package, as originally sold for $109.99. This software is Windows only"

http://www.e-frontier.com/go/shade/85

and the past issue has a copy of carrara V2

 

[WoodWorks]

I found that just was not possible with the STL format file. You get just one big lump, and have to go around assigning textures to individual faces, or more likely individual triangles. Some of the more advanced programs allows multiple triangular face selections so that I could assign texture to many at once.

The big problem I found with most renderers was that they deal with surfaces, and if the vertices are ordered the wrong way, the face reverts to the inside, and the model is transparent in places.

Even ACIS was disappointing as the earlier versions do not support all the features of individual parts, and a lot of the rendering programs do not properly support the later versions of ACIS.

My most promising tests were going through Rhino and using it as a translator, but that will only get you a few models before the trial runs out. Retaining part and face information was my big problem, because without that it can take a long time to apply the proper textures.

Does Maxwell support XGL? Most CAD systems are now providing XGL output. There are very few formats that retain all the informating like STEP, and I found XGL was a good format (it triangulates the faces though). I personally output to STEP, have my wife convert the STEP to XGL using Inventor, and then go to an external rendering program when I need something more complicated then PhotoRender.

The big problem I had with all renderers was retaining the part/object integrity, and there are very few graphic formats that do that.

 

[CGN]

I think what is missing here is a direct translator or a direct way to save form Alibre as a Wavefront format (*.obj), every rendering system use it and is IMO the most close to an standard for 3D than anything else around (talking about Rendering systems and even better than 3d studio files).


I think Shader7 LE can read Iges

 

[MilesH]

Thanks Robert & Kirk.

Yes, you're right, Kirk, I found out yesterday that there is no way to save delimited multibodies in the STL format. All the information is there to be extracted from it, though, as Rhino seems to be able to do the separation.

There are several options to select/propagate triangle groupings in Maxwell, also, it's possible to invert selected face normals. It would be pretty time consuming to use this as the sole way to map a complex model, though...

The other possibility I wondered about was, whether it would be possible to use the API to export an Assembly as individual Part STLs yet retaining their Assembly coordinates. This would solve the Part positioning problem, but I doubt it's doable.

I'll experiment more, going through Rhino.

I tried the Alibre > SAT > 3D DXF > Maxwell route but it was problematic.

No XGS import to Maxwell, yet.

Yes, Robert, if you come across a good translator for STEP to OBJ, please let me know.

It's a pity that the X3D format doesn't have more momentum - maybe now that U3D has been rejected by ISO.... :wink:

 

[MilesH]

Update

Rhino seems to be the solution to this. I was going to wait until V4 came out, but I need it now!

In case anyone else needs to know:

- Import STEP of Alibre Assembly into Rhino.

- Explode.

- Triangulate (Tools/polygon mesh/from NURBS).

- Set scene scale to meters.

- Export (or use Maxwell/Rhino plug-in).

 

[demarchi]

Rhino is an impressive tool. It is complementary to Alibre.
The Alibre plug-in is another big advantage and strenghten this link.
I used Rhino also for splitting a model in order to map mesh a rather complex geometry for a FEM analysis, and it worked smoothly.
Also rapid prototyping shops use it to heal, check and prepare the geometry (be it stp, igs or anything else).

 

[WoodWorks]

I have also spent much time looking for a STEP to OBJ format conversion. While Wavefront OBJ format is a defacto standard rendering format, which I found most rendering programs understand, I did not find much support for retaining part hierachy.

VRML is a promising format, and its new incarnation of X3D. This is a favorite format of the CEO of Okino which makes the Polytrans 3d format converter. He also had little nice (in fact nothing nice) to say about U3D, and indicated it was a rehash of a very poor format standard. It is not suprising it was rejected. I personally have found the Adobe U3D models to be very slow and unresponsive, even on my Athlon 3200+ system.

The Okino website page http://www.okino.com/conv/filefrmt.htm has the best list of file format capabilities, and what I used quite a bit when researching my rendering file import and export formats. You need a format that has a checkmark in the "Hier" column indicating that the format retains the model hierarchy (OBJ and STL do not).

XGL, Rhino, X3D/VRML2 were my final choices. I like X3D the best, but there is still a gap between X3D and STEP. This is where I would concentrate looking for a STEP converter. X3D can be a complicated format and difficult to write a STEP conversion program. Rhino while good software was too expensive just to use as a converter for rendering. Better to use the Rhino rendering package for that price. XGL is a very simple format that is the easiest to read, and possibly the easiest to write a converter from STEP or Alibre.

It seems that most programs that support STEP import do so via the GRANITE tool kit. Not only is it very expensive, it has a difference of opinion with Alibre about the proper construction of a STEP file. So after spending a lot of money, you can still be left with inadequate file translation. When I broached the subject of troubles between Alibre and the Granite tools, they were very unresponsive and insistent that Alibre was at fault (very unwilling to even consider working through the problem, and so I saved myself another $500). I am sure the people at StepTools have a much different opinion of how their software correctly provides Alibre with a properly formated STEP file.

After months of extensive research, I came to appreciate the value of the Alibre Photorendering software. I also became frustrated with the lack of crossover between CAD and Rendering. Don't even get me started on the totally foreign interfaces often present with rendering software, that inhibits casual use as a secondary application.

So if anyone has an answer for our file exchange and rendering woes, please put in your two cents worth because I would really like a direct link from a STEP file to a hierarchical rendering format.

 

[MilesH]

Not so useful for us, but an interesting development:
http://www.nvidia.com/page/gelato.html

Can't say I was that impressed by their gallery, though.....

 

[CGN]

For the Obj file I have found that can "remember" layers, for example once I have the model in rhino I can separate the model and use layers to id the parts, and when saved as a .obj file the file includes the layers so is very easy to turn on and off parts in order to apply shaders or materials on my rendering program.

There is a lot of good render programs and engines available for free like blender for example, but in general is always a pain to go from NURBS to meshes, rhino can handle it very well.

I think I have seen and old free converter for STL to obj I'll try to find it and let you guys know, it was wrote because the programmer need it to go from an old version of solidworks to a rendering program.

Eovia3D.net has a free version of Amapi that can also read iges files and can save as a obj file.

cheers

 

[MilesH]

Re:

I think I have seen and old free converter for STL to obj I'll try to find it and let you guys know, it was wrote because the programmer need it to go from an old version of solidworks to a rendering program.
cheers

Thanks, CGN.

BTW it's STEP to OBJ that we need (it's STL that's causing the problems)

 

[CGN]

I have to say that the best way is to do STEP to render is to render using the Alibre render add-on, there is no way to accomplish such task (Alibre to a rendering software) on an automatic or "magic" way without having to buy a software for it, and even using such some times some tweaking is required...or use other alternatives like export IGES and use some of the free software available and see what works best.

I know is a pain having to go from Alibre to another rendering software without having software like rhino for example, but there are options that yes they may involve a little bit tweaking around but...they are free, and once a way is found on how to do such then there is no much else to learn but enjoy 3 to 6 hours of rendering

I mentioned the STL to obj application because it may help moving models from Alibre to other rendering options for those interested on use another packages at low cost or no cost at all, and this it may not even work.

I use Alibre, Rhino and Carrara

Here are some examples on how to export from a MCAD in this case solidworks, but should give and idea of how you need to tweak files even from so called high end packages, and yes is all about converting to meshes

http://mediawiki.blender.org/index.php/ ... orks_Model