Clipping Plane Always Shows Model as a Shell?

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bejant
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Clipping Plane Always Shows Model as a Shell?

Postby bejant » Thu Aug 08, 2013 6:14 pm

When viewing a section view through my model (View -> Clipping Plane) my model always appears as a shell, rather than a true solid. This happens when I:

1. Select the Sketcher Workbench, create a sketch, and fully restrain it:
Image

change to Part Workbench:
Image

pad the sketch:
Image

then toggle View -> Clipping Plane to on:
Image

and the part appears as a shell rather than a solid:
Image

2. File -> New. From Part Workbench select "Create a sphere solid" Icon, create the sphere, then toggle View -> Clipping Plane to on.
Image
Image

3. Same as #2 above but selecting "Create a box solid".
Image
Image

4. File -> New. From Part Design workbench, select Tasks tab from left window, then select Box, create the box, then toggle View -> Clipping Plane to on.
Image

I was expecting to see the sections as solids, rather than hollow shells. If this is not clear I can post screen grabs. EDIT: Screen grabs included for clarity

Am I doing something wrong?


OS: Windows XP
Platform: 32-bit
Version: 0.14.2192 (Git)
Branch: master
Hash: b63f9d7a2b440e1363508976ec105dac31d7f698
Python version: 2.6.2
Qt version: 4.5.2
Coin version: 3.1.0
SoQt version: 1.4.1
OCC version: 6.5.1
Last edited by bejant on Sat Aug 10, 2013 8:46 pm, edited 1 time in total.
My Part Design tutorials on YouTube (aimed at beginners).
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NormandC
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Location: Québec, Canada

Re: Clipping Plane Always Shows Model as a Shell?

Postby NormandC » Thu Aug 08, 2013 6:44 pm

bejant wrote:Am I doing something wrong?

Nope, I get the same thing.

OS: Ubuntu 12.04.2 LTS
Platform: 64-bit
Version: 0.14.2379 (Git)
Branch: master
Hash: 1e1786fd41993a84e9fe79ab7797a77ddf190c61
Python version: 2.7.3
Qt version: 4.8.1
Coin version: 3.1.3
SoQt version: 1.5.0
OCC version: 6.5.0
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bejant
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Re: Clipping Plane Always Shows Model as a Shell?

Postby bejant » Sat Aug 10, 2013 8:58 pm

Thanks for confirming. I don't know if the parts are actually hollow shells or instead are solids that appear to be shells. This issue has been reported on Mantis:
https://sourceforge.net/apps/mantisbt/f ... hp?id=1208
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NormandC
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Re: Clipping Plane Always Shows Model as a Shell?

Postby NormandC » Sun Aug 11, 2013 3:23 am

Any primitive created in Part workbench or Part Design feature are solids, you can be sure of that. Or, in the case of Part Design features, they will either show as hollow shells (in v0.13.1830) or throw an error (in v0.14 unstable).

My guess would be that the clipping plane is provided by Coin, which is the third-party software library used for visualization, and that it cannot handle solids... But I may be mistaken.
wmayer
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Re: Clipping Plane Always Shows Model as a Shell?

Postby wmayer » Sun Aug 11, 2013 9:36 am

In 3D visualization solids appear always as hollow objects. So, this is definitely not a bug.
freecad-heini
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Re: Clipping Plane Always Shows Model as a Shell?

Postby freecad-heini » Sun Aug 11, 2013 1:56 pm

I guess it's a bug, because in other cad systems like Pro/E or Solidworks the Clipping Plane shows the inner structure of a solid like a solid, not as a surface shell.
Someting must be wrong.
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NormandC
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Re: Clipping Plane Always Shows Model as a Shell?

Postby NormandC » Sun Aug 11, 2013 4:44 pm

wmayer wrote:In 3D visualization solids appear always as hollow objects.

Sorry that's not the case with mid-range commercial CAD software I've used. I mean their clipping plane tools were showing solids.
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bejant
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Re: Clipping Plane Always Shows Model as a Shell?

Postby bejant » Sun Aug 11, 2013 6:11 pm

I was expecting to see something somewhat like this (PTC/Creo example) where it is easy to see if the model is a true solid rather than a hollow shell:
Image

Because wmayer is a developer and confirmed that this is the intended behavior should I delete my Mantis reoprt (assuming I have the rights and am able to do so)?
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ektus
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Re: Clipping Plane Always Shows Model as a Shell?

Postby ektus » Sun Aug 11, 2013 7:39 pm

IMO that's the way it should look like, so the mantis bug is valid. It's the same in CATIA V5R21 and up, previous versions were lacking the capability of showing sections of a single part (as opposed to an assembly).


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Ektus.
wmayer
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Re: Clipping Plane Always Shows Model as a Shell?

Postby wmayer » Mon Aug 12, 2013 5:07 am

The object you see on the screen is a set of triangles (a mesh) which is the output of the tessellation of the shape. Even if the shape is a solid the output mesh is a hollow object in the the first place.

If some applications show these objects as real solids then it means that they do something more. Maybe they do it by running a boolean cut with a plane. So, if we wanted to do it the same way I see some major drawbacks:
* Doing a boolean cut for each solid in the current document might take a long time. Especially when you slightly move the clipping plane do you really want to wait for at least several seconds to see the result? I guess not. A further problem is that from time to time the result of a boolean cut lacks of some faces.

* Then there is major issue if the clipping plane is coincident with a face of the object shape. You can test this with a box. Move the clipping plane this way that it is 100% coincident with one of the faces. Now rotate the object in the 3d view. At some points you will see the whole face, at some other points you will see nothing of the face and at some other points only some parts of it. But what you always see while rotating the object is some heavy flickering.

So, the question is it worth to put a lot of effort into something that theoretically is correct but practically leads to much more problems than before?