Hi Nick, well all NURBS modeling programs have a fitting tolerance that is used for operations that are calculated by a type of refining process, that's not something that's unique to MoI.

MoI generally targets an accuracy of 0.001 units, although I am working on converting to a more adaptable system that will use a fitting accuracy that is some fraction of the object's size which will help to make things work better on little sized objects.

But if you're looking for a system that does not use any kind of a fitting tolerance like that, you'll basically have to rule out every CAD system that's currently in use, since that's just a normal part of how a CAD system operates...

Some CAD systems allow you to specifically set the tolerance to a particular value - unfortunately that often times has a lot of negative side effects, including actually it getting set too loose and making things too inaccurate instead.

But yes, if you have some special need to have manual control over the fitting tolerance you may need to use some kind of special purpose CAD software that has all kinds of intricate settings like that which you may need to attend special training to figure out how to use, lest you set them incorrectly and actually mess things up...

Probably in the future at some point I'll add in a setting that will make MoI target a tolerance of 0.0001 units optionally instead.

Do you have some kind of manufacturing process where you would find a tolerance of 0.0001 units to be inadequate?

One thing to keep in mind is that it is not at all true that more tolerance is automatically better - a tighter fitting tolerance causes iterative algorithms to refine their results more and more, basically causing longer calculation times and also a much larger file size because things like intersection curves will have a zillion control points in them. So just setting the tolerance to some extremely small value is not really a good thing to do, that's something that I've seen as a pretty frequent problem in systems that allow people to set the fitting tolerance to any value at all.

- Michael

And yes that fitting tolerance accuracy only comes into play during particular kinds of calculations that use a kind of refinement process to create their result, like Surface/Surface intersection is one of the main ones.

But for things like entering in coordinates where you're drawing lines and arcs the fitting tolerance does not apply to anything in that case.


So I mean yes definitely the changeability aspect of the constraint systems that MCAD programs offer is definitely useful for editing.

But you should be aware that a fitting tolerance is used in all other NURBS based CAD programs as well - that's not something that's just unique to MoI. If you've assumed that only MoI uses a fitting tolerance and other CAD programs just magically use infinite precision on all operations, that's not correct at all...

- Michael

Solidworks has a rather neat way of dealing with this (if you understand tolerance, that is). If the requested feature or operation cannot be done withing the default tolerance, a dialogue appears showing the minimum tolerance necessary to complete. If you want you can accept the looser tolerance or you can cancel and go back over the model features and find out what caused it.

Maybe this is what Steve refer to : http://help.solidworks.com/2011/English/SolidWorks/sldworks/AllContent/SolidWorks/Core/Surfaces/t_knit_gaps_viewing_selecting_gaps.htm

"""""""""If you want you can accept the looser tolerance or you can cancel and go back over the model features and find out what caused it."""""""""""

Ah yes Steve, and this is the kicker... I have a CAM package that will allow me to set the system tolerance to "15 decimals!!!" If you ask 100 of it's users if it is a good modeler (Capable of making quality solids and surfaces), 96 would say "NO".

Like the abilty to plot the coords for the placement of the b-spline points for the exact curvature of a surface needed at a .0001 tolerance (Instead of having the system do it for you) or recieve poor results...

Has anyone been able to get obj. into the program and been able to work on those or successfully pass then models on to Moi3d
coming from polygons to nurbs .. I am thinking of reverse engeneering....... an Alias program .. Maya does poly to nurbs after all.....???
It also imports Skp ? what for if you cant use them ?
Peter

Import skp works :)
Don't made another try format because no time for that :(

I get a crash with obj as soon as i make another geometry apart from the one imported....
Peter

Hi Peter,
If the poly model is small enough, there is a free utility that will convert an stl to stp.... This will import to MoI as NURBS.. But I have not had success with larger poly sets.

Do I understand you correctly its a polygon to nurbs converter basically a reverse engeneering utility ?
I´d love to know about that !
Peter

Hi Peter,

> I am thinking of reverse engeneering....... an Alias program
> .. Maya does poly to nurbs after all.....???
> It also imports Skp ? what for if you cant use them ?

I don't think this new one has that kind of conversion in it, it seems that you can load polygon objects, but they are a kind of separate object type that can't interact directly with NURBS objects.

So they're more for things like importing a visual reference or something like that and not for actually converting into NURBS geometry.

See this thread on their forum that talks about this:
http://forum.123dapp.com/123d/topics/cannot_extrude_or_fillet_parts_of_an_existing_model


I've heard that Maya does have some kind of function in it for converting sub-d surfaces to NURBS, but it seems that right now the main one that people use for that kind of a thing is the T-splines Rhino plug-in. Also if you use 3DS Max, check out the new nPower converter: http://www.npowersoftware.com/subdtonurbsoverview.htm


I still think it would be cool if the T-splines guys made a simple standalone converter program that could be used for this kind of a conversion without having to buy the entire Rhino + full plug-in combination. Try asking them about that, I've suggested it to them before and maybe if they get enough requests they will cook it up.

Also if you have SolidWorks the T-splines guys have a new plug-in for that as well.

- Michael

I don't test myself but someone say to me that format SAT from 123D to MOI is perfect!
So you can use Free Form or Push Pull / & OR Rotate faces then export to MOI ;)

Hi Petr,

It is here:

http://www.solveering.com/products/products_stl2step.html

The newest version actually works on OBJ instead of just STL.. It converts the poly's to NURBS planes..

It is hit and miss on high polycount models.. Low poly models have worked OK for me.. I had better results with the 1.4 version, but havnt loaded the 1.6 since I changed my OS.. It is a single clcik deploy WPF application, so you may need to be sure you are on windows with the proper .net stuff or something like that..

It's worth a try for what you describe.

Hi Burr,

That sounds fantastic to import some .obj into MoI for modeling reference ...

... but any .obj coming form modo crashs the application :(

Hi PaQ, possibly try triangulating faces first?

Also PaQ, weren't you recently talking about using Rhino some too? In Rhino there is a command called MeshToNurb that will do this (convert each poly face to a flat trimmed plane, not a sub-d conversion).

Just keep in mind that you can end up with an extremely heavy NURBS model with that method, because there is more overhead to how trimming boundaries work in NURBS models - there's stuff like a 3D edge curve, as well as a 2D edge curve, and the curves are actual splines that are created in addition to vertices.

In a poly mesh model, the edges are more lightweight and basically just implied as straight lines connecting each vertex, so it's more efficient with polys to have something like 300,000 edges in a mesh, whereas 300,000 edges in a NURBS b-rep is huge.

Of course since each edge in a NURBS brep is a general spline you can get a whole lot more out of a single edge in NURBS because it can be an actual curved piece of geometry and not just a line between 2 vertices. That's why you can get a complex model in a NURBS brep with something more like 5,000 edges or faces since each individual edge or face describes a bigger curved piece of the model. But by making each surface a little plane and each edge just a line you're basically negating that.

- Michael

Hi Michael,

I havn't decide yet to pushase rhino yet, I'm still using the pl version, and my export/save count is over since a while.
Seems like the 5.0 is coming this year too, so I'll maybe wait a little bit more (900$ is still a little amount of money especially
for an hobby kind of use).

Thanks for the little explanation about the conversion process, the kind of object I want to use is probably a little bit too heavy
to this process.

As for the convertion crash, I'm using a really low triangulate object for testing (2000 tris), without success.
Maybe it's a data precision problem, the log file report this : 'La conversion de la chaîne "0.0173325" en type 'Single' n'est pas valide' (sorry for the french).

Not sure I have to will to debug the problem with the Solveering LLC guys, I even have no idea how expensive is the pro version :S.

 

- Back to the topic :

123D didnt work for my son at all, the viewport manipulation is to weird for him. It was funny to see him bitching about all the popups too :)
MoI is definivelety much better for kids ;)

Hi Paq,
I havnt used the OBJ import yet, but will load it and look too, to see if I notice anything.. But for sure, the app is sensative....

Hi PaQ,

> Maybe it's a data precision problem, the log file report
> this : 'La conversion de la chaîne "0.0173325" en type
> 'Single' n'est pas valide' (sorry for the french).

Probably not precision, but more likely an internationalization bug - you must have a locale set in Windows that uses the comma character as the decimal point separator?

That program is probably expecting then that numeric data should use a comma as the decimal separator, but that's not the case in OBJ files - OBJ use the period as the decimal separator for numeric values.

Try switching your Windows locale setting to English, or possibly just set the decimal separator setting to a period (as shown in this post here: http://moi3d.com/forum/index.php?webtag=MOI&msg=4282.5) and then maybe that other program will work.

If that does work, then that's a bug in that program, it's using a locale-specific number parsing method instead of using a method that will always use the period as the decimal separator.


> 123D didnt work for my son at all, the viewport manipulation
> is to weird for him. It was funny to see him bitching about all
> the popups too :)

I'm not too surprised, it's hardly different from their regular version which is targeted towards mechanical engineers basically...

I bet your son could learn it if he was introduced to it as part of a class instead of just trying to figure it out directly.

- Michael

Hi PAQ,
I just did a test with Hexagon and an OBJ import/conversion with the newer stl2step converter..

I revieved the error also from a default export from Hexagon.. I then did an export and deselected "Export UV's and Export Normals" and the import into stl2step succeeded!



I havnt tested to see if it was one or the other yet, and I dont know what you have in Modo upon export, but you may look at eliminating some of this information from the export to get the model in... :o