Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 1 Oct 1999 14:02:26 GMT
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Viewed:
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1355 times
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Leonardo Zide wrote in message <37F383E1.CA6B8962@centroin.com.br>...
> "Lars C. Hassing" wrote:
> > In addition to Leonardo's summary:
> > Because the "what is inside/outside" of e.g. 4-4cyli.dat depends on the
> > usage, and we don't want two sets of primitives, I think we need to
> > decide on a "0 CCW" or "0 FACE CCW" or ?? keyword.
> > (see the discussion I started on Feb 4th 1999)
>
> About that discussion, IMO it would be better to have *everything* CCW
> instead of adding a keyword. Most primitives can have their faces
> changed by using mirroring so we probably won't need to have 2 sets,
> only make the current files have the same orientation.
I agree with John Van in that we need three keywords: CCW, CW, UNKNOWN.
As the rendering program is going to keep track of the number of mirrorings of
the transformations (or simply if the total transformation is a mirroring), we will
need a way to tell what is inside-out side of e.g. cylinder primitives.
Then STUD2.DAT could use:
0 CCW
1 16 0 -4 0 4 0 0 0 4 0 0 0 4 4-4cyli.dat
0 CW
1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
or maybe to make it easier to use for part authors:
1 16 0 -4 0 4 0 0 0 4 0 0 0 4 4-4cyli.dat
0 INSIDE-OUT 1
1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
0 INSIDE-OUT 0
Whether it will be:
"0 CCW", "0 CW", "0 UNKNOWN"
"0 FACE CCW", "0 FACE CW", "0 FACE UNKNOWN"
"0 ORIENTATION CCW", "0 ORIENTATION CW", "0 ORIENTATION UNKNOWN"
"0 INSIDEOUT 0", "0 INSIDEOUT 1"
I don't have any meaning about (though I don't like the first one :-)
A part with no keywords is interpreted like it had begun with "0 FACE UNKNOWN".
The only use for the UNKNOWN keyword I can see, is for a section of a part you
want to make compliant at a later time.
/Lars
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Message has 3 Replies:
 | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| Lars C. Hassing wrote in message <938787015.279086@ns.cci.dk>... (...) of (...) we will (...) Hold on. Why not just have a button in the CAD program to turn the part inside-out by automatically manipulating the orientation matrix in the parent dat (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
| | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| (...) Why not simply: (...) Assuming the primitives are all defined so their faces are turned outward. I would see allowing both CW and CCW as a convenience for parts authors. There's no real difference between one way and the other. CW has a slight (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| (...) When you draw a part with a pattern transparently, I guess it's not a good idea to remove the backfaces or you might not see the pattern from some angles. (...) About that discussion, IMO it would be better to have *everything* CCW instead of (...) (25 years ago, 30-Sep-99, to lugnet.cad.dev)
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