Hi Michael G.

I could not find any settings in Alibre for STEP export, but I imported the same Alibre AP 203 Step file into ViacAD, TurboCAD Pro and IronCAD's Inovate and they all came in correct to scale in millimeters.

The steps you showed me earlier work fine, but my concern is that if someone were to receive a STEP or SAT file from Alibre and open it in MoI without paying attention, they could be heading for disaster downstream. Normally I would be working in the reverse, bringing MoI data into Alibre, but I wanted reference geometry for a test when I discovered this.

I'll go ahead and try the other import/export file types between Alibre and MoI and let you know what I find out.

Michael T.

Hi MichaelT - if I open up the STEP file in Rhino, I get units set to cm in there.

Also if you open up the STEP file in a text editor like notepad, you can actually scroll down and see that the units seem to be set to centimeters, this is the relevant part of the file:

#99=(
LENGTH_UNIT()
NAMED_UNIT(*)
SI_UNIT(.CENTI.,.METRE.)
);

There seems to be some problem in MoI's STEP importer that is not reading in that units setting properly though. I'll explore this some and find out if this can be fixed, it may be something that needs to be fixed by the author of the import libraries that MoI uses.


> but I imported the same Alibre AP 203 Step file into
> ViacAD, TurboCAD Pro and IronCAD's Inovate and they
> all came in correct to scale in millimeters.

They seem to be converting from the centimeter units that are actually set in the file into mm.

I guess that those systems are working more like MoI's import command where the units setting retains its current setting when opening that file and instead the imported file is scaled to convert into the current unit system, rather than the current unit system actually getting set to what was in the file.


> if someone were to receive a STEP or SAT file from Alibre
> and open it in MoI without paying attention, they could be
> heading for disaster downstream.

Actually the SAT file seems to be working fine as far as units go - when you open the file up in MoI you get the units set to cm with the part in the proper size in centimeters.

I also double checked the SAT file by directly loading it into notepad as well, and in its header it is marked as having the units in the file as cm as well - the setting for that is not as easy to see as the STEP file one, it comes from the 3rd line in the file which says:

10 9.9999999999999995e-007 1e-010

The 10 there at the front of that line means that each numeric unit in the file represents 10mm , or in other words the numbers stored in the file are stored as centimeters.

- Michael

Hi Michael T - I also did a couple of simple tests with some basic shapes like a box out of Alibre and into MoI using STEP format, and these tests seem to bring the unit setting (in cm) over into MoI ok.

So there seems to be some problem dealing with something in your specific model, it seems to be having some problem with the cylinder piece on it and I guess that may be causing an error during the import process which makes it not get to handle reading in the units setting as it is supposed to.

Could you also give a try with a simple shape like a box to verify that works ok?

I've sent your STEP file to the author of the import libraries that MoI uses to ask why the units are not read in for that particular case, he may be able to figure out what is going wrong.


You may also want to try IGES format for getting your model over.


Thanks,
- Michael

Hello, new member here.

Just to add to this thread.
I am a freelance design draughtsman and have been using Alibre as my parametric modelling software for around 4 years and think it is excellent. Having used Inventor & Solidworks extensively I prefer to use Alibre for various reasons.

My surface modelling experience is limited having only experienced it in ACAD. Anyway I would just like too say I am completely hooked on MOI (only had it for a few days since the Alibre offer) it is easy to learn, has a great looking and simple interface giving excellent results.

Every credit to you Michael.... Brilliant !!
Thank you.

Alexander

Hi Michael G.,

I just had the same STEP file issue with a SolidWorks STEP file I downloaded from the web. I have attached it here. The same SAT file came in okay.

Just thought I would let you know.

Michael T.

Hi Alexander, thanks very much - I'm glad that you like MoI!

- Michael

Hi Michael T,

> I just had the same STEP file issue with a SolidWorks STEP
> file I downloaded from the web. I have attached it here. The
> same SAT file came in okay.
>
> Just thought I would let you know.

Thanks for posting the file Michael T - this looks like another problem with reading the units setting from the file, but it is a different problem than the previous one.

I've heard back from the STEP library author for the previous problem and he has a fix coming for it in the next version of the library. I'll also send him this other one and see if that can also be fixed.

The problem with this new one seems to be that the library thinks the units in the file are supposed to be meters, when I guess they are actually in inches. This seems to be due to some kind of alternate method used for designating the units, it's got these entries in the STEP data:

#5130 =( CONVERSION_BASED_UNIT ( 'INCH', #5131 ) LENGTH_UNIT ( ) NAMED_UNIT ( #5132 ) );

#5133 =( LENGTH_UNIT ( ) NAMED_UNIT ( * ) SI_UNIT ( $, .METRE. ) );


The library seems to be not handling or taking into account that "Conversion based unit" stuff in the file.


In order to fix this second one into MoI, you'll need to turn off the option to scale objects when the unit system changes, then change the units from meters into inches, then turn the option to scale back on and then change the units to mm to get the correct final result in mm.

- Michael

Hi Michael G.

Yep, that does it.

I will still try some of the other file conversions between these various programs, and let you know my results.

Thanks again,

Michael T.

Hi Michael T, so I found out what is going on with that second STEP file, the one from SolidWorks - it's actually a bug in MoI and not in the STEP import library itself.

It's possible for STEP files to store not only a unit system but also a scale factor that is supposed to be applied to the unit system as well, and MoI was not paying attention to this additional scale factor.

So for example that file you posted has 1 unit = 1 inch in size, but for whatever reason instead of it just directly saying that the units were inches, it instead was set to say that the units were meters with an additional scale factor of 0.0254 applied to it (which is 1 inch in meters). But MoI was only picking up on the meters setting part and not the additional 0.0254 scale factor part.

So I've added that to my list of stuff to fix in MoI. Thanks for posting the example file,

- Michael

No problem,

Always glad to try to help.

Michael T.