POV-Ray : Newsgroups : povray.bugreports : Is sphere_sweep known to be troublesome? Server Time
15 Apr 2024 15:43:19 EDT (-0400)
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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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From: Woody
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 01:40:03
Message: <web.4baeea5d2e5cb7c2876671bb0@news.povray.org>
Almost forgot.

Is this something that can be fixed in the future version or the next beta?


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From: Thorsten Froehlich
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 04:33:38
Message: <4baf1462$1@news.povray.org>
On 28.03.10 07:25, Woody wrote:
> 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.

No, that code uses a linear spline for which bounding works.

	Thorsten


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From: clipka
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 09:43:16
Message: <4baf5cf4@news.povray.org>
Am 28.03.2010 10:33, schrieb Thorsten Froehlich:
> On 28.03.10 07:25, Woody wrote:
>> 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.
>
> No, that code uses a linear spline for which bounding works.

Given that the bug reported by the OP has two components - garbled 
geometry /and/ a missing bounding box - I'd rather say yes, as far as 
the garbled geometry is concerned.


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From: Woody
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 10:40:01
Message: <web.4baf697d2e5cb7c2c41e4df50@news.povray.org>
Thorsten Froehlich <tho### [at] trfde> wrote:
> On 28.03.10 07:25, Woody wrote:
> > 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.
>
> No, that code uses a linear spline for which bounding works.
>
>  Thorsten

I'm assuming when you refer to bounding you are referring to the specific
bounding mentioned in the documentation at
http://www.povray.org/documentation/view/3.6.1/323/

When doesn't this work?
For what type of splines?
I'm having trouble choosing a bounding box, or size and position, that gets rid
of these unwanted effects.

Any suggestions?


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From: Thorsten Froehlich
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 12:01:17
Message: <4baf7d4d$1@news.povray.org>
On 28.03.10 15:43, clipka wrote:
> Am 28.03.2010 10:33, schrieb Thorsten Froehlich:
>> On 28.03.10 07:25, Woody wrote:
>>> 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.
>>
>> No, that code uses a linear spline for which bounding works.
>
> Given that the bug reported by the OP has two components - garbled
> geometry /and/ a missing bounding box - I'd rather say yes, as far as
> the garbled geometry is concerned.

The geometry problems are the result of the bounding going wrong.

	Thorsten


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From: clipka
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 13:36:54
Message: <4baf93b6$1@news.povray.org>
Am 28.03.2010 18:01, schrieb Thorsten Froehlich:

> The geometry problems are the result of the bounding going wrong.
>
> Thorsten

No, definitely not - geometry code *MUST NOT* rely on any undesired 
surfaces being eliminated by bounding - if only because rotating the 
object may grow the bounding box.


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From: Thorsten Froehlich
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 18:06:55
Message: <4bafd2ff$1@news.povray.org>
On 28.03.10 19:36, clipka wrote:
>> The geometry problems are the result of the bounding going wrong.
>>
>> Thorsten
>
> No, definitely not - geometry code *MUST NOT* rely on any undesired
> surfaces being eliminated by bounding - if only because rotating the
> object may grow the bounding box.

I think there is some miscommunication: I am not saying that the bounding 
and the object depend on each other in any unusual way. I am just saying 
that for certain cases with cubic splines the bounding will be too small.

	Thorsten


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From: clipka
Subject: Re: Is sphere_sweep known to be troublesome?
Date: 28 Mar 2010 19:16:13
Message: <4bafe33d$1@news.povray.org>
Am 29.03.2010 00:06, schrieb Thorsten Froehlich:

> I think there is some miscommunication: I am not saying that the
> bounding and the object depend on each other in any unusual way. I am
> just saying that for certain cases with cubic splines the bounding will
> be too small.

Well, that's what we /will/ see once the bounding has been 
"quasi-fixed". But obviously it's not what we're seeing in the OP's 
scenario.


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