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 21:08:55 GMT
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Viewed:
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491 times
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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
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Message has 1 Reply:
 | | Re: Primitives and quads/triangles
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| (...) I use Steve's rotate spreadsheet to figure out what cones/rings I need to fit into a space. Go here to get it: (URL) use the Rings tab. Enter the inner and outer radius and the y height. Then choose a cone primitive and set the scales and (...) (22 years ago, 16-Oct-02, to lugnet.cad)
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Message is in Reply To:
| | Re: Primitives and quads/triangles [DAT]
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| (...) 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! Now I need to find out how type 5 lines (...) (22 years ago, 16-Oct-02, to lugnet.cad)
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