Subject:
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Re: 1-8sphe.dat tesselations compaire image
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Newsgroups:
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lugnet.cad
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Date:
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Tue, 3 Oct 2000 14:01:59 GMT
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Viewed:
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624 times
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4 days ago I've posted that I've made a compaire image showing the two
possible alternatives for surface tesselations for the 1-8sphe.dat primitive.
I've waited a while before giving my own opinion, but here it is:
For me, the proposed alternative for the tesselation, using 16 triangles per
sector, has no substantial benifit over the tesselation as used in the
existing official primitive, using 9 quads and 4 triangles per sector.
My arguments:
The inaccurate coordinate values that the old 1-8sphe.dat primitive still had,
have been resolved with a fix submitted by Axel Poqué and I in August this
year. (This fix is part of the recent 2000-02 update)
I think that face distribution with 9 quads and 4 triangles isn't a
disadvantage compaired with Travis Cobbs his distribution with 16 triangles.
In the compaire image http://members.ams.chello.nl/mmoolhuy/compaire.jpg
it seems to me that the existing 9 quads and 4 triangles tesselation is even
better looking that the proposed 16 triangle alternative. In my opinion, the
dome on the right looks a little smoother than the dome on the left.
Calculation of intersection points with other faces is easyer for the existing
primitive than for the proposed alternartive.
However, I appreciate that Travis did made an effort, and hope I haven't
discouraged him to make other contributions in the future. After all, he was
right in saying that (at least) the accuracy of the old primitive had to be
improved.
References for those of you who want to do some research of their own:
My compaire image followed a proposal by Travis Cobbs to replace the
1-8shpe.dat primitive. See this mail and its follow-ups:
http://news.lugnet.com/cad/dat/parts/primitives/?n=70
My mail containing the link to the compaire image:
> Recently Travis Cobbs proposed to replace the existing 1-8sphe.dat primitive
> with an alternative that uses a different tesselation of the sphere surface.
> (tesselation is the way in wich a curved surface is represented by dividing it
> into plane quads and/or triangles)
>
> For the benefit of those who want to have a say in this choice, I've
> constucted an image where whan can compaire the effects of the proposed
> tesselation agains the current one. This image can be viewed at:
>
> http://members.ams.chello.nl/mmoolhuy/compaire.jpg
>
> On the left is the proposed "Travis Cobbs"-method, which uses
> 16 triangles per sector.
> On the right is te existing "James Jessiman"-method, which uses
> 9 quads and 4 triangles per sector.
>
> Tecnical data of the picture:
> The objects you see are two identical 4-4cyli.dat primitives (radius 100),
> each topped with a dome consisting of four 1-8sphe.dat primitives of the
> appropriate tesselation type.
> I've rendered the picture with L3Lab,
> Shading: on,
> and Color Scheme: 3 Ldlite+Mlcad
>
> Because Travis Cobbs proposed primitive hasn't type 5 lines yet, I've also
> turned Show Line Type 5 off, to have a fair comparison.
> The background has been manualy changed into white.
>
> Greetings, M. Moolhuysen
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Message has 2 Replies:
 | | Re: 1-8sphe.dat tesselations compaire image
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| I agree with Manfred's conclusions. I'd also like to add that if Travis had made his submission at a different time, so we didn't have the alternative, I would have been very happy to accept his version of the primitive. Another thought: what about (...) (24 years ago, 3-Oct-00, to lugnet.cad)
| | | Re: 1-8sphe.dat tesselations compaire image
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| "Manfred Moolhuysen" <moom@nospamchello.nl> wrote in message news:G1uxnB.I8H@lugnet.com... (...) primitive. (...) per (...) had, (...) triangles. (...) even (...) the (...) existing (...) was (...) be (...) Works for me. Don't worry about the (...) (24 years ago, 4-Oct-00, to lugnet.cad)
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Message is in Reply To:
| | 1-8sphe.dat tesselations compaire image
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| Recently Travis Cobbs proposed to replace the existing 1-8sphe.dat primitive with an alternative that uses a different tesselation of the sphere surface. (tesselation is the way in wich a curved surface is represented by dividing it into plane quads (...) (24 years ago, 29-Sep-00, to lugnet.cad)
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