Hi Michael,

first of all, thanks for your answer.

I tried to export a 3DM from solidThinking but the result is bad, I purchased MoI v1 to access the Beta 2 and with the STEP file the result is great, but is still not perfect in some areas.

I attached a movie so you can see the problem (try to scrub forward and backward to see the problem).

Is the "STEP" file a better format for convert Nurbs to polygonal or is better to use the 3DM file format?

If I export an IGES from solidThinking and I open it with MoI I can't join the surface, is this a problem of the IGES?

I also attached the model in 3DM, STEP and IGES

Thanks

Antonio Corona

> I tried to export a 3DM from solidThinking but the result is bad,

Yeah, the geometry in the 3DM file appears to be corrupted. I get a similar bad result when trying to open the same file in Rhino as well, here is a screenshot of what it looks like in Rhino:



Also Rhino's "Check" command reports a large number of geometry errors, looks like something about an incorrect vertex structure.

So as far as I can tell solidThinking is not exporting that geometry properly to the 3DM file.


> Is the "STEP" file a better format for convert Nurbs to
> polygonal or is better to use the 3DM file format?

Normally I'd recommend to use 3DM format because that has less calculations that need to be done by MoI on the imported geometry. STEP format tends to only contain the 3D curve parts of trimming curves, making it necessary for MoI to calculate the UV space parts of the trim curves which can be difficult in complex situations.

But in this case it looks like the export from solidThinking to 3DM is buggy so for this particular case it looks like you can't use 3DM.


> If I export an IGES from solidThinking and I open it with MoI
> I can't join the surface, is this a problem of the IGES?

It's probably a tolerance issue, the surfaces are probably not touching close enough for them to be joined in MoI. MoI requires that edge are within 0.005 units of one another in order to join them together to make a shared edge.

I also get a similar result of join failures when importing the file into Rhino and trying to join it in there.


> I attached a movie so you can see the problem (try to scrub
> forward and backward to see the problem).

I couldn't really see what the problem was when running the video at a normal rate. It seems to be very subtle?

That's probably some polygonal artifact that can happen just when rendering polygons that are large in size.

What does the wireframe of your mesh look like in Modo? Does it have some longer tall polygons for the back side piece?

If so, then try breaking those long polygons up into smaller pieces by using the "Divide larger than" setting at export time in MoI. Having smaller polygons can tend to reduce certain kinds of polygonal rendering artifacts.

Remember - polygons are not actually truly smooth objects at all, they are little flat pieces that kind of emulate a smooth surface by doing some tricks. When you have smaller polygons, that can reduce some of the artifacts that can come from not having truly curved surfaces.

See here for some examples of using "Divide larger than" for the MoI export:

http://moi3d.com/forum/index.php?webtag=MOI&msg=2833.5
http://moi3d.com/forum/index.php?webtag=MOI&msg=1084.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=1549.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=804.26


If you produce a more finely diced up mesh, it should probably help to reduce your rendering artifacts.


- Michael

Thanks Michael,

I have understand where is the problem talking with the company that build it in solidThinking:
The model was created initially using solidThinking by company A, then saved in the STEP format and a company B have modified it using another modeler (I don't know the name).

If I open the model done initially by company A in solidThinking and I save it in IGES, then with MoI I save in LWO the result is perfect.

Is IGES better than STEP for this kind of conversion?

I attached the file if you want to check.

Antonio

Hi Antonio,

> Is IGES better than STEP for this kind of conversion?

Unfortunately there isn't really a single format that is always better than the others in all circumstances, sometimes in one particular case one format may be better and then in a different case another one may be better.

Each format does things a little differently.

The main problem with IGES is usually that only individual surfaces are stored in the IGES file and then the receiving application needs to take all those individual surfaces and figure out how to join them to one another to make a solid which can sometimes be a complex process.

In STEP, the objects are stored as solids (the connections between surfaces are stored and do not need to be calculated manually), but STEP has a different issue where only the 3D edge curves are used for trimming boundaries, forcing the application to calculate the UV space curves of each trimming boundary from the 3D edges. With complex edge structures (especially when edges are nearby a surface seam), that can be a complex process.

Any complex process can tend to cause problems, the more complex a process is the more possibility for things to go wrong.


Anyway, it sounds like you have resolved your issue using the original model?

- Michael

> Anyway, it sounds like you have resolved your issue using the original model?

Absolutely, thanks again for your precious help.


Bye


Antonio

Is the "Manifold Solid B-Rep Object Entity (Type 186)" in IGES not used? or is it a weaker implementation as in STEP? or does it not even describe the true solid?

Hi Kevin,

> Is the "Manifold Solid B-Rep Object Entity (Type 186)" in IGES not used?

Historically it is just not as common as individual surfaces.


> or is it a weaker implementation as in STEP?

I don't really know off the top of my head exactly how IGES entity 186 compares to object structures in STEP. But I kind of think they are generally similar in idea though.


> or does it not even describe the true solid?

IGES entity 186 I believe does describe a true solid.

- Michael

Great!

I love reading this forum, I've learnt so much from your excellent technical advise to situations all of us run into (shelling errors, fillet problems)
And the fact that this is software independent means the advise applies to many different modeling packages and situations.
So valuable!