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Here are two pics, related to the 'hexagonalized torus' thread I
started earlier. Each picture consists of 6 wavy sphere sweeps
each going around the torus four times, each containing
approximately 100 points. Each sphere sweep is supposed to be
a closed path, with identical first and last point.
When I did this with 'linear' sphere sweeps the paths closed
as they should [picture not shown]. But with 'cubic_spline'
and 'b_spline' sweeps the paths failed to close, even though
the first and last points were identical. The first picture
shows six gaps, upper right slightly on back side of torus.
In the second picture I fixed this by overlaping the start and
the tail of the paths, not by one but by TWO points. It was
a surprise to me that I would have to do this.
Here are the pics.
--
Jim Buddenhagen
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Attachments:
Download 'torus_hex_test7_4b_spline2_640.jpg' (35 KB)
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Preview of image 'torus_hex_test7_4b_spline2_640.jpg'
Preview of image 'torus_hex_test7_4b_spline_fixed_640.jpg'
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James Buddenhagen nous apporta ses lumieres en ce 2005-04-28 09:55:
> Here are two pics, related to the 'hexagonalized torus' thread I
> started earlier. Each picture consists of 6 wavy sphere sweeps
> each going around the torus four times, each containing
> approximately 100 points. Each sphere sweep is supposed to be
> a closed path, with identical first and last point.
>
> When I did this with 'linear' sphere sweeps the paths closed
> as they should [picture not shown]. But with 'cubic_spline'
> and 'b_spline' sweeps the paths failed to close, even though
> the first and last points were identical. The first picture
> shows six gaps, upper right slightly on back side of torus.
>
> In the second picture I fixed this by overlaping the start and
> the tail of the paths, not by one but by TWO points. It was
> a surprise to me that I would have to do this.
>
> Here are the pics.
> --
> Jim Buddenhagen
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
When using the cubic_spline, the first and last points are *only* control points. When
using
b_spline, the start and end "spots" are somewhere around the second and second to last
points. The
exact position depend of the position of the first and third points for the starting
point. Both
need at least 4 points.
Alain
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James Buddenhagen wrote:
Some spline types need extra points before and after any calculated
point. The reason you needed to overlap by two is that not only was the
"tail" short, but the "head" didn't start until the second point.
I don't used sphere sweep, but I imagine that even though the ends are
now touching, with certain spline types, the curve might still not be
continuous without even more overlap. This is true with the POV-Ray
natural_spline which IIRC might never be completely continuous at joined
ends, but which gets *more* continuous with more overlap.
-Shay
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"Alain" <ele### [at] netscape net> wrote in message
news:4270f087$1@news.povray.org...
[...]
> When using the cubic_spline, the first and last points are *only*
> control points. When using b_spline, the start and end "spots"
> are somewhere around the second and second to last points. The
> exact position depend of the position of the first and third
> points for the starting point. Both need at least 4 points.
>
> Alain
My thanks to both you and Shay for explanations.
--
Jim Buddenhagen
Post a reply to this message
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