Still a need for an ACIS (SAT) importer/exporter?

[Epy]

We might've discussed this before, but I was looking through the long-term goals and one of them is a SAT importer/exporter. In AutoCAD 2013, you can import STEP and IGES, and export IGES only (without add-ons). Older versions of AutoCAD couldn't import/export STEP or IGES IIRC. I am not sure what version added this capability, but in any case AutoCAD 2013 is "old" now.

Should we still aim for this? Are there any other extensions we should aim to support?

[Jim]

On Wednesday, 25 November 2015 09:49:35 UTC+11, Epy wrote:

We might've discussed this before, but I was looking through the long-term goals and one of them is a SAT importer/exporter. In AutoCAD 2013, you can import STEP and IGES, and export IGES only (without add-ons). Older versions of AutoCAD couldn't import/export STEP or IGES IIRC. I am not sure what version added this capability, but in any case AutoCAD 2013 is "old" now.

Should we still aim for this? Are there any other extensions we should aim to support?

FreeCAD users seem to want much better DXF, DWG, support.

Would your ACIS import/export be able to extract the ACIS within DXF, are they these two ACIS the same thing?

[Epy]

ACIS would be for .sat files, which can be imported/exported from AutoCAD. Chances of DWG support are nil, but 2D DXF entities shouldn't be a problem for anyone.

[thatcadguy]

My mistake, seems you are right that DXF does indeed have ACIS text embedded in REGION, BODY, etc. entities.

[thatcadguy]

So it seems the hangup with this is really that there are only fragments of the standard available on the internet, and most pretty old. ACIS is currently on version 25, so in this case if I'm understanding correctly from reading that means 25 versions of SAT files to support, though a lot may be the same. On the DXF side, things are somewhat spotty. There doesn't seem to be a really good quality C/C++ library; there are a lot out there, most licensed GPL. The best I've found is ezdxf which is MIT licensed, but written in Python.

I would like to get DXF and SAT import/export functionality into OCE, any guidance/thoughts in this area (mostly for the SAT part) would be appreciated.

On Tuesday, November 24, 2015 at 2:49:35 PM UTC-8, thatcadguy wrote:

[Normand Chamberland]

Hello,

I'm sorry, but regarding ACIS support, you do realize you are talking about reverse engineering a closed-source modeling kernel file format? I have no programming experience, I am just an experienced CAD user who's had an interest in various CAD tools. But is it a realistic goal for an open source project with so few resources? AFAIK, apart from Roman Lygin's CAD Exchanger (which is not open source), software libraries supporting closed-source CAD file formats are only available from a few specialized software companies.

And why support ACIS (SAT), and not Parasolid, or Granite (PTC) or CGM (Catia's native kernel format)? I'd wager that Parasolid has more market share than ACIS. (SolidWorks for example uses Parasolid, as well as new kid on the block cloud app Onshape)

It's been said in this thread that FreeCAD users want better DXF/DWG support. Certainly *some* users do as this subject is recurring in the FreeCAD forums, but I do not believe that embedded 3D data is a main concern. Most of them care about 2D import, which may not be in OCE's purview.

Also, to add more confusion to this topic, Autodesk forked the ACIS kernel back in 2001, when ACIS was at version 7.0. Since then they have developed their own modeling kernel called ShapeManager, even though they seem to use ACIS as their SAT import/export format. I haven't used AutoCAD in quite a few years, so I can't recall if it could import ACIS files saved in a higher version than 7.0 (I doubt it). And who knows if 3D DXF/DWG embeds 3D data in ACIS format, or in Autodesk's own ShapeManager format? How much does it differ from ACIS after so long?

https://en.wikipedia.org/wiki/ShapeManager

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[Jake]

Hi Normand,

I have gone through the project's long term goals (https://github.com/tpaviot/oce/wiki/Long-term-goals) a few times and ACIS import/export is one of those goals. Simply aiming to follow through with that. The file format itself is not too intimidating (it is somewhat human-readable) and at some point the file format was supposed to be made available: http://www.thefreelibrary.com/ACIS+format+goes+public.-a017421415 , but it seems that yes, it is closed. In my searching I actually found a forum post from 2009 by Roman Lygin asking Spatial for a copy of the file format specification and they basically told him to buy a license for their exchange libraries.

In an ideal world it would be wonderful to support all those formats! In the 3D CAD world I would agree that Parasolid has a greater share, but in the 2D world I think AutoCAD (and its related formats) are the de facto standard. So yes, in regards to the next point, maybe 2D DXF import/export is only important and therefore the 3D (SAT) part is not as important. 

Maybe we all ought to take this opportunity to discuss CAD interop as a long-term goal, as in what all we should aim to support, what is realistic, and what is most important. I am not worried about our limited resources, I have a lot of free time and there's always someone who wants to come along and contribute. My goal with working on the SAT support was to put together something that partially worked at least and then after probably a few years of patches and extra help, we would have something much more usable. There's always Google Summer of Code too for some extra help.