Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Possible replacement for 1-8sphe.dat
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Newsgroups:
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lugnet.cad.dat.parts.primitives
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Date:
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Thu, 21 Sep 2000 08:00:10 GMT
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Viewed:
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630 times
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I started a discussion on the .dev group regarding sphere tesselation a
little while back, and it came out that there is some dissatisfaction with
the current sphere primitive. I have finished the code which generates a
replacement sphere primitive, and hacked together a little routine to output
it to a .dat file. Below is the result.
Please note that I have not yet generated linetype 5 lines. I will only go
to the trouble to do that if there is interest in using my generated version
as a replacement for the original one. I generated the data to 3 decimal
places. Is this an appropriate number?
One thing that should be noted is that a triangular tesselation of a sphere
which contains 16 segments around its equator produces a sphere with
significantly different break-down of facets than the existing sphere file.
The existing 1-8sphe.dat file contains 9 quads and 4 triangles. The
individual triangles are each less than half the surface area of the
individual quads, producing an unbalanced distribution. In addition, the
quads are either non-planar, don't fall on the surface of an actual sphere,
or both. My replacement tesselation is made up of 16 triangles, all of
which have a similar surface area. In addition, all of the vertices fall on
the surface of an actual sphere (once you account for rounding).
Here is my file:
0 1/8 Sphere
0 Author: Travis Cobbs
0 Incomplete suggested replacement for 1-8sphe.dat primitive.
0
0 I will produce linetype 5 lines if there is interest in
0 using this as an actual replacement for 1-8sphe.dat.
0
0 This data was generated using the algorithm used by LDView to
0 perform sphere primitive replacement. (The sphere primitive
0 replacement feature has not yet been released.)
0
3 16 1.000 0.000 0.000 0.924 0.000 0.383 0.924 0.383 0.000
3 16 0.924 0.000 0.383 0.784 0.439 0.439 0.924 0.383 0.000
3 16 0.924 0.000 0.383 0.707 0.000 0.707 0.784 0.439 0.439
3 16 0.707 0.000 0.707 0.439 0.439 0.784 0.784 0.439 0.439
3 16 0.707 0.000 0.707 0.383 0.000 0.924 0.439 0.439 0.784
3 16 0.383 0.000 0.924 0.000 0.383 0.924 0.439 0.439 0.784
3 16 0.383 0.000 0.924 0.000 0.000 1.000 0.000 0.383 0.924
3 16 0.924 0.383 0.000 0.784 0.439 0.439 0.707 0.707 0.000
3 16 0.784 0.439 0.439 0.439 0.784 0.439 0.707 0.707 0.000
3 16 0.784 0.439 0.439 0.439 0.439 0.784 0.439 0.784 0.439
3 16 0.439 0.439 0.784 0.000 0.707 0.707 0.439 0.784 0.439
3 16 0.439 0.439 0.784 0.000 0.383 0.924 0.000 0.707 0.707
3 16 0.707 0.707 0.000 0.439 0.784 0.439 0.383 0.924 0.000
3 16 0.439 0.784 0.439 0.000 0.924 0.383 0.383 0.924 0.000
3 16 0.439 0.784 0.439 0.000 0.707 0.707 0.000 0.924 0.383
3 16 0.383 0.924 0.000 0.000 0.924 0.383 0.000 1.000 0.000
--Travis Cobbs (tcobbs@san.REMOVE.rr.com)
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Message has 6 Replies:
 | | Re: Possible replacement for 1-8sphe.dat
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| (...) I think your both of your files are significant improvements over the existing primitives. My only concern is the possible impact changing the primitive could have on other files, where surfaces intersect spheres, but not at the edges of the (...) (24 years ago, 21-Sep-00, to lugnet.cad.dat.parts.primitives)
| | | Re: Possible replacement for 1-8sphe.dat
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| (...) I think these should have 4 decimal places, as with the majority of the circular primitives. The reason for this is that there is often a need to use 3DPs in parts. Where these include circular primitives and scale them up by a factor of 10 (...) (24 years ago, 21-Sep-00, to lugnet.cad.dat.parts.primitives)
| | | Re: Possible replacement for 1-8sphe.dat
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| I'm sorry for breaking my reply up intp little pieces, but for an unnown reason I'm not able to post any long message to Lugnet for the past 4 days. (...) Please make that 4 decimal places, for all the other curved primitives that the 1-8sphe.dat (...) (24 years ago, 22-Sep-00, to lugnet.cad.dat.parts.primitives)
| | | Re: Possible replacement for 1-8sphe.dat
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| (...) Following an initiative by Axel Poqué, I've resubmitted an improved version of the original 1-8sphe.dat primitive for the next update. This version still has 9 quads and 4 triangles, but coplanarity and meeting the surface of the sphere falls (...) (24 years ago, 22-Sep-00, to lugnet.cad.dat.parts.primitives)
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