Hi there,

For certain projects I have to deal with many different CAD files from many different sources. Most of them don't come as 3DM, of course, but IGES, STEP, or files I have to convert on my own first, like SolidWorks. Usually, I import them as STEP 214 into MoI and don't see distinct problems there. But I wondered if STEP is really the best import format for MoI in means of object geometry, curves, and so on. So, my question here is just what import format should I choose when I have the choice? :-)

I use SolidWorks, Inventor, Rhino at work. And i use MOI to repair IGES and STEP from various systems. If your CAD file is a valid volume in Inventor or SolidWorks, you could try Acis Sat. If i am correct, that is Moi3d's mathematical kernel and should work better. But sometimes i can load IGES and STEP files in Moi3d that would kill Inventor or Soldidworks. As far as i can tell, there is no easy way to say, this type works 100% all of the time.

MoI's kernel is NOT ACIS, but Solids++........

The default MoI format is 3dm.

When importing, there are "2 things" to look into (IMO)

1= WHAT you are importing.
2= FROM WHERE you are importing it.

MoI's importers are 3rd party, so they are little programs that read the different formats.

What? Solid entities you may try STEP. That will try to maintain the original defined solid object. Surfaces and curve entities, I would look at iges. SAT and others I would look more at where they come from.

So from where? if you can find out the app that created the files, that can lead you towards what format will best bring in the file. ACIS or Parasolids or was it a third party export also, etc........

So iges, will have a good definition of surfaces and curves etc, and try to do "stitching" and such on import, to make joined surfaces and solids and line joins etc...
STEP will try to maintain solids and original stitching params etc (So from other apps, you can see very coarse seems etc, when tolerances are different.)
ACIS is it's own animal and third party exporters and importers can create "breaks", or surface trims where the original file had none. (nothing really wrong with those, unless they will interfere with further modeling, etc)

Also, some of these formats can be "custom". So a particular company can have a proprietary "ACIS" SAT format, which can further make problems with importing a "SAT" from that type of app (Same goes for STEP)

So, if you can have enough information about the "2 questions", that can lead you towards which format is best. If YOU ARE DOING the file format conversion, then you should have those answers already.

2 cents.

Hi 3image, yeah like Burr mentions it can be a little complicated and may even depend on the source and maybe even on the particular geometry being translated. Each format kind of has its own particular tricky things with it.

STEP format is probably a good bet for the main one to try. The part that's good about STEP is it can transfer the edge joining information so solids come through directly. The area where it can be difficult is that some programs transfer 3D trim curves that can cross over the closing seam of a surface, so when imported into a program like MoI which defines trims with a matching UV and 3D space curves those seam-crossing trims have to be detected and split where they cross the seam. Usually it's not a problem but if the curve kind of wavers around just slightly around the seam it can end up being a difficult calculation.

IGES format doesn't have the seam-crossing difficulty but instead usually only contains a lot of trimmed surfaces without any joining information and so the joining has to be done as another import step and in some situations that can also be a difficult calculation.

SAT is I guess kind of similar to STEP.

Curves are more straightforward in all the formats, any format really should be fine for curves.

I'd say you'd probably normally want to use STEP format, and if you run into a problem where a couple of surfaces are messed up with mangled trim boundaries try a different format for that particular model. If you're working with an ACIS based program like ViaCAD for example it may be good to use SAT as a first choice though especially exporting from MoI because it seems like that involves the least amount of possible mutation and processing when going into ACIS.

- Michael