Which 3D format?

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NormandC
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Re: Which 3D format?

Postby NormandC » Fri Apr 21, 2017 1:25 am

davecoventry wrote:My client is concerned that the STEP files can be deconstructed into drawings of individual parts.

Dave,

A compound is a type of entity specific to the OCC kernel (and possibly to commercial geometric kernels but I can't be sure); as far as I know it is not part of the STEP specification. STEP is by design a CAD exchange format: it will produce solids and surfaces if it encounters them in a file. A compound is a container of shapes; since STEP doesn't recognize compounds, it will display as separate all the shapes that were contained in it.

To my knowledge a method to restrict the way it makes shapes available has not been implemented into STEP; I dare say that it would totally defeat the purpose of the file format. What you're asking almost amounts to implementing some kind of DRM.

As for parts failing to fuse, one of the possible reasons is that you are trying to fuse together solids and surfaces, and/or the resulting shape would be invalid or non-manifold, knowing the OCC kernel's weakness with Boolean operations the list could be long. You would need quite a big amount of work to get your model to be a single "monolith".

You have to question the reason for providing a disabled CAD model. What's your customer's intent with this model? Why would they share your CAD model to a third-party if they fear it can be reverse engineered by whomever they share it with?

If this 3D file is only for visualization purposes, why not provide a mesh file as already suggested? A quick test on a simple model shows Stanford Triangle Mesh (*.ply) to make the smallest file amongst the mesh formats FreeCAD supports (2.5x smaller than STL).
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davecoventry
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Re: Which 3D format?

Postby davecoventry » Sun Apr 23, 2017 8:46 pm

Hi NormandC,

Thanks for the insight.

Yes, the customer wants to be able to use the model to incorporate into the 3D model of his plant.

My client is the guy who invents, manufactures and sells the equipment and he is unhappy at providing a model which may be rendered down into individual parts as manufacturing drawings.

The customer has suggested to my client that STEP drawings can be generated which cannot be so disassembled, and I wanted your opinion on whether this is possible and if it is how may it be achieved.

I guess you're right that it is a manifestation of DRM [spit!], but the industry is rife with copying, and while there's nothing to prevent a customer buying a machine and then dismantling it so that he can replicate it and possibly sell it on, I can see why my client is unwilling to provide him with a set of working drawings.
~ Dave
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NormandC
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Re: Which 3D format?

Postby NormandC » Sun Apr 23, 2017 9:14 pm

Hi Dave,

davecoventry wrote:The customer has suggested to my client that STEP drawings can be generated which cannot be so disassembled

You are talking about "STEP drawings", but in my experience with a few professional CAD programs, I've never seen drawings (which by definition are 2D) in STEP format, only 3D models. The would-be intellectual property thief would actually need to create drawings from the components in the STEP model.

I'm afraid there is simply no absolute way to prevent someone from extracting manufacturing information from a STEP model. Even if you spent valuable time to fuse your whole model into a single blob (something that you may not be able to do), for example in FreeCAD it would not be so difficult to explode it and recreate the individual components. Time consuming yes, impossible definitely not.

Sorry I don't see an easy solution to your problem...
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easyw-fc
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Re: Which 3D format?

Postby easyw-fc » Sun Apr 23, 2017 9:58 pm

davecoventry wrote:The customer has suggested to my client that STEP drawings can be generated which cannot be so disassembled

Hi,
as I suspected you were talking of semplifying the model to avoid as much as possible the reverse engineering...
The techniques I suggested are exactly in that direction...
FC is an open source CAD, so these aspects are not very important ... commercial sw are more used to this...
if you google a bit you can find:
https://forum.solidworks.com/thread/49793
https://synergiscadblog.com/2014/06/10/ ... operty-ip/

Particularly the first link is in some way achievable using the method I suggested (use FC0.17)
model.FCStd
(5.5 KiB) Not downloaded yet

1) export your model as STEP
model.step
(16.25 KiB) Not downloaded yet

2) open your STEP model and select all parts
3) Part Join Connect objects
4) (Convert to solid your connected part) this may be not necessary
5) refine it
6) export the final object as STEP
model-connected-refined.step
(54.12 KiB) Not downloaded yet

at this step it should already a group of external surfaces...
so the next steps would not be probably needed
7) re-open the new STEP file
8) export it as IGES (select Group of trimmed surfaces type144)
9) reopen the IGES select the object and export it as STEP
Now the STEP model should be composed only by the external surfaces of your model
model-connected-refined-surfaces.step
(87.14 KiB) Not downloaded yet

You can see from the image that the cylinder and the torus are not defined internally into the final model, as they are instead in the step initial model; so you will get only the external geometry in the final model.
surfaces.png
surfaces.png (222.85 KiB) Viewed 54 times

(obviously if your model has detached parts, those will have to be managed singularly)

But as @NormandC already pointed out, there is no protection that full covers everything...
there are even techniques to get a 3D mechanical model from a scan or an stl model
http://cdn-streaming.spaceclaim.com/Rev ... view_D.mp4

Maurice
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davecoventry
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Re: Which 3D format?

Postby davecoventry » Mon Apr 24, 2017 8:52 am

Hi NomandC, Maurice,

Thanks for the suggestions and the info.

I have (sort of) found a solution which is to import the model into Blender as a .OBJ and export as a DXF.

The problem is the the resulting file size is blimmin yyuuuuuge! A bit messy as well, despite me using "Dissolve Vertices".

I'm not necessarily looking for complete protection through obfuscation, but I need to make it harder to use the model to generate manufacturing drawings.
~ Dave
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easyw-fc
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Re: Which 3D format?

Postby easyw-fc » Mon Apr 24, 2017 11:47 am

davecoventry wrote:I'm not necessarily looking for complete protection through obfuscation, but I need to make it harder to use the model to generate manufacturing drawings.


Hi Dave,
looking deeper I found also this link @ Pro/E which is explaining this external geometry approach when sharing 3D models
http://www.cadlab.tuc.gr/proehelp/aax/about_s0.htm

Maurice