Subject:
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Re: Primitives and quads/triangles
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Newsgroups:
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lugnet.cad
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Date:
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Wed, 16 Oct 2002 21:37:26 GMT
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Viewed:
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1656 times
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In lugnet.cad, Travis Cobbs writes:
> In lugnet.cad, Niels Karsdorp writes:
> > I have created a fourth version, using primitives for cylinders and rings.
> > Cones I have created with 16 segment quads for LDraw and a true cone for
> > PovRay (using 0 L3P IFPOV etc.). The results are great!
>
> Looks good in my program (LDView), once I got the file modified back to its
> original form due to the posting causing some lines to wrap.
>
> Looking at the file, I think it would require new cone primitives to allow
> the use of cone primitives instead of quads. The outer cone has an outer
> radius of 19 and an inner radius of 16 (assuming I'm interpreting the POV
> code correctly).
>
> Since 19 is prime, a 4-4con18 file would probably be necessary. The
> exisiting 4-4con8 file can be used with this for the rest by multiplying the
> part of the transformation matrix that effects the radius by 2. It would
> also be tricky to line up perfectly, because you have a height of 4 (-6 to
> -10), but a radius difference of 3, so your height multiplier would have to
> be 4/3 for the outer 4-4con18 file, and 8/3 for the inner 4-4con8 file.
> Round-off error would probably result in a visible gap.
>
> So I think it would be very difficult to produce good results using any kind
> of cone primitive.
>
> As for the type 5 lines, they are fairly easy in this case. You'll have one
> type 5 line for each face on the cones. The first two points will represent
> the shared points between two faces. The other two points will be taken
> from the opposite side of each of the two shared faces. I'll try to draw
> two faces:
>
> a*** ***e
> * ***d*** *
> * * *
> b*** * ***f
> ***c***
>
> The above is an attempt at representing two adjoining quads. You might have
> to click the "View Raw Message" link right above Reply if you're viewing
> this with the web interface. The type 5 line would be made of the following
> 4 points (in order): c, d, b, f. There are other combinations that would
> work, but the preceding will work.
>
> --Travis Cobbs
I use Steve's rotate spreadsheet to figure out what cones/rings I need to
fit into a space. Go here to get it: http://www.geocities.com/partsref/
Just use the Rings tab. Enter the inner and outer radius and the y height.
Then choose a cone primitive and set the scales and postion correctly and
everything should mesh perfectly.
-Orion
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Message has 1 Reply:
Message is in Reply To:
 | | Re: Primitives and quads/triangles
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| (...) Looks good in my program (LDView), once I got the file modified back to its original form due to the posting causing some lines to wrap. Looking at the file, I think it would require new cone primitives to allow the use of cone primitives (...) (24 years ago, 16-Oct-02, to lugnet.cad)
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