Reliable format for drawing exchange between different CAD systems?

[carlharr]

Hello all, I'm wondering if anyone can offer any suggestions.

We often receive DXF files from suppliers as a "drawing exchange" format, to be imported into our own drawing borders.
However the results from import to NX are flaky at best, with objects moving / vanishing, and text frequently changing.

Looking at the DXF format on Wikipedia, it's clear that DXF imports are difficult because DXF isn't a "standardised" format.

http://en.wikipedia.org/wiki/AutoCAD_DXF

And these DXFs are normally exported from other systems (e.g. Pro-E), on other set-ups with different fonts installed etc. etc., compounding the problems.

The final risk is that even if a DFX import to NX looks ok, there's no way to check it against the original.

I'm frequently asked for help importing DXF, as they almost never work.



So the question is:

For solid models, there are published industry standard exchange formats (STEP & IGES) for one system to another.
But is there something similar for 2D drawings?

NX can create CGM exports, and with text set to polylines these should be bulletproof.
So does anyone know if all the other major CAD systems can also export and import CGM e.g. Pro-E, Catia, AutoCAD etc.?

Or does anyone have any advice on a reliable 2D format that they use between systems?

Thanks in advance, Carl

http://www.jcb.com

NX 8.5 with TC 8.3

 

[stephlouv]

Few times I had to deal with dxg or dwg, the result was far from clean ...
(Yes, sorry, in general, I'am allergic to what is coming from AutoCad)

I really do like CGM. It's the lower level vectorized 2D that exist I think.
It's lightweight, even if it is several MB, it can be crazy zipped.
To me it is the 2D version of an IGES.
Other CAD software should read it.
Even MSoffice applications can open it if the appropriate import filter have been installed.

In 2D vectorized, there is also WMF (windows Meta File). You know it, the cliparts.

"My english is bad ? That's why i'am french."

 

[cowski]

I believe the IGES format can import/export 2D drawing data. I've never used it for drawings, so I don't know if it is any better than DXF...

www.nxjournaling.com

 

[carlharr]

stephlouv,

I also like CGM and think of it as the 2D version of 3D standard exports.
But my experience is only with NX.

You say other CAD systems should read it, does anyone else know this for sure?
And also importantly, are they able to create CGMs.


cowski,

I just had a go with 2D Iges - many options to choose from, which worries me when you can't control the source data.
And unfortunately, my own import of my own export failed!!

http://www.jcb.com

NX 8.5 with TC 8.3

 

[cowski]

Given my past experience with IGES, I'm not surprised.

Import/export is always tricky; you never quite know if you need to tweak your import settings or if some feature was used during export that your software doesn't support yet. If you continue with DXF, you might want to download one or more of the free 'viewers'. That will at least give you a 'second opinion' of what the output should look like.

From the wiki article you linked to, it sounds like DWG may be your best bet...

www.nxjournaling.com

 

[carlharr]

It does look like DWG may be better but again, if this is coming from e.g. CATIA, we are talking about a translation (outside of our company) from one system to another CAD format, then a second translation into NX. This still concerns me, instead of using a "standardised" exchange.

I have looked at the Autodesk viewer and it's pretty good, so I may recommend our engineers ask for it installing on their machines. But of course this only shows the result of an export (and on a different system, so maybe a fonts effect too?), and not the original drawing.

Hence why I wondered if anyone has experience with other formats for sharing drawings with suppliers / customers.

I may just ask them to try different methods and let me know how it goes!

http://www.jcb.com

NX 8.5 with TC 8.3

 

[Toost]

I use Autodesks DWGTrueview to check DXF and DWG files. Its a free viewer.
Since it's from the source company of the DXF/DWG format i see it as the "arbitrator" to decide if the file is ok or not.
( Note, this does not mean that i like the file formats or the viewer...)

The main issue in my perspective is DXF/DWG -3D, not 2D. 2D works somewhat. 3D does not.


Regards,
Tomas

 

[MikeHyde]

Carl

I have had some issues with CGM, as there are 2 different methods of producing them -it's something to do with the way it translated text. A few years ago I had to import both types of CGM into NX on different sheets and pick out the best bits to create the drawing. It was importing from Catia which could have contributed to the problem - Catia doesn't seem to like communicating with other CAD systems.

Overall I have found CGM to be more stable than DXF.

Mike Hyde

http://www.astonmartin.com

NX8.5 with TC9.1

 

[carlharr]

Mike,

It sounds like this is text to text, or text to polylines. If you export to text it's stored as a font, and this relies on the font working with the "reader" as well. In our case we can't export to font from NX, and then read with Vis on the same machine!

The better CGM option is export to polylines, which treats text as curves. This to me is probably the most reliable drawing exchange format.

Tomas,

That's the DXF viewer I've got also. My only concern is that I'm still not seeing e.g. the original CATIA file, but checking this way should still be better than nothing.

http://www.jcb.com

NX 8.5 with TC 8.3

 

[cowski]

This still concerns me, instead of using a "standardised" exchange.

Even a 'standard' such as STEP is a moving target; unless the application is reading in its native file format, I'd say it is all translations. Differences in drawings can occur even in NX when opening a .prt file from an earlier version...

www.nxjournaling.com

 

[carlharr]

I miss File > Print...

http://www.jcb.com

NX 8.5 with TC 8.3

 

[carlharr]

Thank you for your help all, I've put together some advice which is (in brief)
1. ask for a different (system independent) format e.g. CGM, with text as polylines
2. try DWG instead, which should be more reliable
3. request a PDF or JPEG to check the import against - v important

http://www.jcb.com

NX 8.5 with TC 8.3

 

[Toost]

Carl,
if Catia exports something in DXF/DWG format, and it doesn't look good in the dwgtrueview, i would ask the sender for a better file. That's what i was trying to say in my previous post.

 

[UGperson]

Catia will import and export CGM file just fine. You could also insert a .jpg or .tiff file into the drawing. The tiff/jpg has a bug when you export the drawing you sometimes get a double image in the area of the tiff/jpg.

 

[carlharr]

Hi Thomas, yes I understood, it is a good viewer. My only concern really was having an "original" to compare the view against, which is why I've suggested to our engineers number 3 above.

Hi UGperson, that's good to know for future. I would guess most systems could do CGM, although I was told once AutoCAD can't. Whether that's true or not I don't know.

In any case, hopefully I've provided enough information now so that our engineers can carry on without me!

http://www.jcb.com

NX 8.5 with TC 8.3