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From: Kenneth
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 05:10:01
Message: <web.4ba8839e2e5cb7c265f302820@news.povray.org>
"Kenneth" <kdw### [at] earthlinknet> wrote:
> Warp <war### [at] tagpovrayorg> wrote:

> >   Manually specifying a bounding box for the sphere sweep object should fix
> > that problem.
>
> Did a test, and that does indeed work; the OP's object renders MUCH faster, and
> the artifacts are confined to the bounding shape. (Remove_Bounds=on needs to be
> in the INI file, though; I don't know how that might affect 'bigger' scenes.
> With it off--the default--POV issues a non-fatal warning, "Unnecessary bounding
> object removed" and eliminates the bounding object.)

Sorry, I made a major blunder there (I hate it when that happens!) The default
for Remove_Bounds is ON, not off. So it's natural that POV will remove the
manually-added bounded_by object, when using the default setting.

To clarify:  The bounded_by object is used correctly by setting
Remove_Bounds=off, OR by setting Bounding_Threshold to 1 or 0. (The OP's scene
has only one object, so Bounding_Threshold needs to be set at that or lower for
automatic bounding to kick in.) In which case, it doesn't seem to matter
if Remove_Bounds is on OR off. A bit of a mystery, but a bit-off topic too.

Ken


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From: Warp
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 11:57:07
Message: <4ba8e4d3@news.povray.org>
Kenneth <kdw### [at] earthlinknet> wrote:
> Sorry, I made a major blunder there (I hate it when that happens!) The default
> for Remove_Bounds is ON, not off. So it's natural that POV will remove the
> manually-added bounded_by object, when using the default setting.

> To clarify:  The bounded_by object is used correctly by setting
> Remove_Bounds=off, OR by setting Bounding_Threshold to 1 or 0. (The OP's scene
> has only one object, so Bounding_Threshold needs to be set at that or lower for
> automatic bounding to kick in.) In which case, it doesn't seem to matter
> if Remove_Bounds is on OR off. A bit of a mystery, but a bit-off topic too.

  I understood your mistake the first time, and it doesn't change my opinion
that POV-Ray removing by default your manual bounding object from the sphere
sweep is a design mistake worth of a bug report.

  It may be a good idea to remove a manual bounding box eg. if it has been
applied to a sphere primitive, because in that case the bounding box will
only make rendering the sphere slower. However, in the case of a sphere
sweep this is clearly not a case, hence a special case is warranted.

-- 
                                                          - Warp


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From: Thorsten Froehlich
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 12:08:49
Message: <4ba8e791$1@news.povray.org>
On 18.03.10 17:29, Warp wrote:
> Kenneth<kdw### [at] earthlinknet>  wrote:
>> (Remove_Bounds=on needs to be
>> in the INI file, though; I don't know how that might affect 'bigger' scenes.
>> With it off--the default--POV issues a non-fatal warning, "Unnecessary bounding
>> object removed" and eliminates the bounding object.)
>
>    IMO that's a design mistake in POV-Ray worth of a bug report.

It is an ancient but with the spline interpolation bounding computations not 
working. It has been known ever since sphere_sweeps where added to POV-Ray 
(as the bug existed in the original source). It was even discussed back then 
( 3.5 beta), but nobody ever volunteered to implement the somewhat 
complicated mathematical solution to computing the correct bounding for 
spline based sweeps :-(

	Thorsten


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From: Warp
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 13:12:25
Message: <4ba8f678@news.povray.org>
Thorsten Froehlich <tho### [at] trfde> wrote:
> On 18.03.10 17:29, Warp wrote:
> > Kenneth<kdw### [at] earthlinknet>  wrote:
> >> (Remove_Bounds=on needs to be
> >> in the INI file, though; I don't know how that might affect 'bigger' scenes.
> >> With it off--the default--POV issues a non-fatal warning, "Unnecessary bounding
> >> object removed" and eliminates the bounding object.)
> >
> >    IMO that's a design mistake in POV-Ray worth of a bug report.

> It is an ancient but with the spline interpolation bounding computations not 
> working. It has been known ever since sphere_sweeps where added to POV-Ray 
> (as the bug existed in the original source). It was even discussed back then 
> ( 3.5 beta), but nobody ever volunteered to implement the somewhat 
> complicated mathematical solution to computing the correct bounding for 
> spline based sweeps :-(

  My point was that POV-Ray *removing* the manually-specified bounding box
from the sphere sweep by default is a design mistake which should be changed.

  I understand it's not trivial to calculate a bounding box automatically,
but removing the user-defined one shouldn't be done. There should be some
exception for sphere sweeps (and perhaps some other heavy objects) so that
manually-specified bounding boxes are always preserved for them.

-- 
                                                          - Warp


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From: Christian Froeschlin
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 14:51:03
Message: <4ba90d97$1@news.povray.org>
>   My point was that POV-Ray *removing* the manually-specified bounding box
> from the sphere sweep by default is a design mistake which should be changed.

As far as I understand it, the point of removing manual bounding
is to speed up the rendering of scenes designed before POV-Ray 3.0.
In all later scenes manual bounding was added with the intent of
overriding the automatic bounding anyway. So maybe 3.7 might be
a good time to change the default for Remove_Bound to "off"?


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From: clipka
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 16:04:06
Message: <4ba91eb6$1@news.povray.org>
Warp schrieb:

>   It may be a good idea to remove a manual bounding box eg. if it has been
> applied to a sphere primitive, because in that case the bounding box will
> only make rendering the sphere slower. However, in the case of a sphere
> sweep this is clearly not a case, hence a special case is warranted.

Sounds like opening up too many special cases, and the question which 
objects should be treated that way and which shouldn't.

Why not simply output a warning whenever user-specified bounding boxes 
are removed, regardless of object type?

If a user decides that he needs the bounding box, he can then just 
change the .ini file or command line parameters accordingly and live 
happily ever after.


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From: Warp
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 23 Mar 2010 17:21:49
Message: <4ba930ed@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Why not simply output a warning whenever user-specified bounding boxes 
> are removed, regardless of object type?

  Because default behavior should be that of the least surprise.

  Nowadays nobody adds bounding shapes to objects (this was only the case
with POV-Ray 2.x and earlier, where automatic bounding was poor or even
inexistent), so it would be better to *not* remove bounding boxes by default,
and have the automatic removal as an option to be specified in the ini file.

  I'm not exactly sure anymore, but I have a faint memory that POV-Ray doesn't
actually remove bounding objects from infinite objects (such as quartics).
If that's the case, then sphere_sweep could simply be flagged as "infinite"
to get that behavior.

-- 
                                                          - Warp


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From: Thorsten Froehlich
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 24 Mar 2010 06:09:33
Message: <4ba9e4dd$1@news.povray.org>
On 23.03.10 22:21, Warp wrote:
>    I'm not exactly sure anymore, but I have a faint memory that POV-Ray doesn't
> actually remove bounding objects from infinite objects (such as quartics).
> If that's the case, then sphere_sweep could simply be flagged as "infinite"
> to get that behavior.

That would cause various other problems along the way...

	Thorsten


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From: Kenneth
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 24 Mar 2010 07:30:01
Message: <web.4ba9f7112e5cb7c265f302820@news.povray.org>
> Christian wrote:
> As far as I understand it, the point of removing manual bounding
> is to speed up the rendering of scenes designed before POV-Ray 3.0.
> In all later scenes manual bounding was added with the intent of
> overriding the automatic bounding anyway. So maybe 3.7 might be
> a good time to change the default for Remove_Bound to "off"?

> Warp wrote:
> Nowadays nobody adds bounding shapes to objects (this was only the case
> with POV-Ray 2.x and earlier, where automatic bounding was poor or even
> inexistent), so it would be better to *not* remove bounding boxes by default,
> and have the automatic removal as an option to be specified in the ini file.

and (taken out of context)
> Because default behavior should be that of the least surprise.

I agree. It seems to me that this would eliminate (from the user's standpoint)
any question about which situations are *special cases* and which are not. (A
CSG merge vs. a sphere_sweep, for example.) And would likewise require less
thinking when constructing a scene. E.g., "I've added a bounded_by shape, so now
I need to change Remove_Bounds to OFF--I think."

BTW, experimenting (in v3.6.1) with the OP's scene, going through all the
permutations of
1) adding/not adding a bounded_by shape
2) Remove_Bounds on/off
3) Bounding threshold at default vs. 0 or 1
produces some non-intuitive results for certain cases.

Here's one:
bounded_by object added
Bounding_Threshold=0 or 1
Remove_Bounds=on (default)

Surprisingly, this sucessfully uses the bounded_by object (possibly replacing
the sphere_sweep's own 'automatic' bounding shape)--yet Remove_Bounds is ON, and
POV issues the "bounding object removed" warning anyway.  Perhaps this is some
*special case* concerning just the sphere_sweep, I don't know.  But all in all,
knowing 'what to do when' with any particular object is rather confusing, as is
the error message.

Ken


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From: Woody
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 01:30:06
Message: <web.4baee84b2e5cb7c2876671bb0@news.povray.org>
Sorry for joining the conversation late. I only saw the thread after making the
post at

http://news.povray.org/web.4baed21667547a80876671bb0%40news.povray.org

It appears ot be of the same problem.

Can someone let me know the modifications I need to make to the original code at
the beginning of the post (or better yet my own code) to get rid of the extra
shapes in the sphere sweep?

I'm not sure I understand how the bounding box will help? Is it applied to the
whole sweep or each individual sphere component (know sure how that would be
done). Is it applied in place of or in conjunction with the scaling mentioned in
the original post? For that matter I'm not sure I understand how the scaling
mentioned works?

Sorry If this seems dense I'm a little lost.

-Jeff


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