Unusable Helix Projections

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ulrich1a
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Unusable Helix Projections

Post by ulrich1a »

Im am modelling cooling water lines with tubing coils. When I try to make a drawing out of it, the projections in the drawing page are unusable for a technical drawing. I have made a simple example to show this. The top projection is only a simple line instead of the expected ring. The lower projection has not all hidden lines correctly removed. The curves at the tube turns are disturbed.
helix_projection.png
helix_projection.png (38.78 KiB) Viewed 3028 times
Is this a bug in FreeCAD, in OpenCascade or do I something wrong?
Attached are the document and a script to create the part.

Ulrich

OS: Windows 7
Word size of OS: 32-bit
Word size of FreeCAD: 32-bit
Version: 0.15.4527 (Git)
Branch: master
Hash: 0da2e4c45a9a259c26abd54c2a35393e1c15696f
Python version: 2.7.8
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 6.7.1
Attachments
spring.zip
(533 Bytes) Downloaded 41 times
helix_projection.FCStd
(32.76 KiB) Downloaded 48 times
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shoogen
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Re: Unusable Helix Projections

Post by shoogen »

ulrich1a wrote:do I something wrong?
No
ulrich1a wrote:Is this a bug in FreeCAD
unlikely
ulrich1a wrote:in OpenCascade
Yes, but it's so severly that i would rather call it a limitation.
In fact we are using the hidden line removal, for a purpose that might extend way further then their originally intended usage.
As this won't be resolved shortly, please open a ticket in our bug tracker.
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shoogen
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Re: Unusable Helix Projections

Post by shoogen »

helix-Shape2DView.png
helix-Shape2DView.png (11.95 KiB) Viewed 3017 times
This much is OCCT's fault. The deformed arcs in the drawing are probably caused by FreeCAD.
ulrich1a
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Re: Unusable Helix Projections

Post by ulrich1a »

I have issued a bug report: http://www.freecadweb.org/tracker/view.php?id=1937
I OpenCascade 6.8 were reported, that there a tolerance problem with the hidden line removal was improved. But it did not help either. :?

Ulrich
ulrich1a
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Posts: 1957
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Re: Unusable Helix Projections

Post by ulrich1a »

I made a test with an older FreeCAD-release under wine. For me it looks more like a regression.
The Draft-projection still is the same with a lot of not hidden lines:
helix_projection_Draft_0.14.2512.png
helix_projection_Draft_0.14.2512.png (10.25 KiB) Viewed 2983 times
Whereas the Drawing-Workbench produced a nice projection:
Helix_projection0.14.2512.png
Helix_projection0.14.2512.png (45.3 KiB) Viewed 2983 times
The projection from top of the helix produced also only a straight line.
Are there only subtle differences in the call of the projection function?

Ulrich

OS: Windows XP
Platform: 32-bit
Version: 0.14.2512 (Git)
Branch: master
Hash: e157152c962fe1fe5340dbe825f31f1e21f9a09a
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
ulrich1a
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Posts: 1957
Joined: Sun Jul 07, 2013 12:08 pm

Re: Unusable Helix Projections

Post by ulrich1a »

I had still some older Versions on this computer. The disturbed curves were introduced between

OS: Windows 7
Platform: 32-bit
Version: 0.14.3044 (Git)
Branch: master
Hash: 843838ec194010197dcaf9e5d83d55f253d2ac03
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

and

OS: Windows 7
Platform: 32-bit
Version: 0.14.3071 (Git)
Branch: master
Hash: 15406d1498e284739fd921d6fdc071905601b34b
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

Ulrich
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shoogen
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Re: Unusable Helix Projections

Post by shoogen »

There is only one commit in between git commit 9c5f1c216d2428cdbfb6ddab5752569fbd26768e
Looks like I'm to blame :o

But I'm still convinced that the approximation paramerers (number of segments and allowed tolerance) are unsuitable.
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shoogen
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Re: Unusable Helix Projections

Post by shoogen »

With maxsegs=50 and OCC version: 6.8.1.dev-27a6612 i get
helix-maxsegs_50.png
helix-maxsegs_50.png (20.02 KiB) Viewed 2949 times
ulrich1a
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Re: Unusable Helix Projections

Post by ulrich1a »

What makes me wondering was, that with OCCT 6.5.1 the Draft-Projection had a lot of visible lines that should have been hidden, whereas with the same FreeCAD-version and the same OCCT-version the Drawing-Projection was not perfect, but a lot better. So there seems to be something different in the projection-call from the Draft-workbench compared to the projection-call from the Drawing-workbench.
Unfortunately I have no actual build with OCCT 6.5.1 in order to check, if all the hidden lines in the Drawing-projection are caused by a different OCCT.
Your picture from the last post is a Draft-Projection or a Drawing-Projection?

Ulrich
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shoogen
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Re: Unusable Helix Projections

Post by shoogen »

ulrich1a wrote:Your picture from the last post is a Draft-Projection or a Drawing-Projection?
Drawing

One problem is that OCCT returns 8 groups of edges.
VCompound // hard edge visibly
Rg1LineVCompound // Smoth edges visibly
RgNLineVCompound // contour edges visibly
OutLineVCompound // contours apparents visibly
IsoLineVCompound // isoparamtriques visibly
HCompound // hard edge invisibly
Rg1LineHCompound // Smoth edges invisibly
RgNLineHCompound // contour edges invisibly
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