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From: Roman
Subject: sphere_sweep doesn't scale
Date: 13 Dec 2013 05:55:05
Message: <52aae789@news.povray.org>
Hi there,

The minimal scene file below should produce identical images for any 
value of the scaling factor s, but it doesn't. s=1e-1 works fine, s=1e-3 
produces individual spheres instead of a sweep, and s=1e-5 makes the 
object fully invisible. The code for sphere_sweep doesn't seem to scale.

Using other values for the sphere_sweep tolerance and turning off the 
bounding (-MB) doesn't solve the problem.

This might be related to http://bugs.povray.org/task/81, as I'm getting 
the artifacts described there as well for intermediate scaling factors, 
but the problems described here appear to be much more severe.

I'm using POV-Ray 3.7 on OpenSUSE 12.2.

Regards,
Roman



// START MINIMAL SCENE FILE

#version 3.7;

#declare s = 1e-3; // 1e-1: ok, 1e-3: individual spheres, 1e-5: invisible

camera {
	location 7*z
	look_at 0
	scale s
}

light_source {
	<20,25,40>, rgb 1
	scale s
}

sphere_sweep {
	cubic_spline
	5,
	< 2.4,-2.1,0>, 1
	< 0.8,-0.9,0>, 1
	<-0.6, 0.4,0>, 1
	<-1.8, 1.7,0>, 1
	<-2.8, 2.0,0>, 1
	scale s
	pigment { color rgb 1 }
}

// END MINIMAL SCENE FILE


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Attachments:
Download 'sphere_sweep_problem_1e-1.png' (3 KB) Download 'sphere_sweep_problem_1e-3.png' (3 KB) Download 'sphere_sweep_problem_1e-5.png' (1 KB)

Preview of image 'sphere_sweep_problem_1e-1.png'
sphere_sweep_problem_1e-1.png

Preview of image 'sphere_sweep_problem_1e-3.png'
sphere_sweep_problem_1e-3.png

Preview of image 'sphere_sweep_problem_1e-5.png'
sphere_sweep_problem_1e-5.png


 

From: Thomas de Groot
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 07:15:47
Message: <52aafa73$1@news.povray.org>
I wonder if you can /scale/ a camera? In the docs section about 
transforming the camera, this is /not/ mentioned as such, only rotate 
and translate, so maybe there lies the problem.

Thomas


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From: Le Forgeron
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 07:50:34
Message: <52ab029a$1@news.povray.org>
Le 13/12/2013 11:55, Roman a écrit :
> Hi there,
> 
> The minimal scene file below should produce identical images for any
> value of the scaling factor s, but it doesn't. s=1e-1 works fine, s=1e-3
> produces individual spheres instead of a sweep, and s=1e-5 makes the
> object fully invisible. The code for sphere_sweep doesn't seem to scale.
> 
> Using other values for the sphere_sweep tolerance and turning off the
> bounding (-MB) doesn't solve the problem.
> 
> This might be related to http://bugs.povray.org/task/81, as I'm getting
> the artifacts described there as well for intermediate scaling factors,
> but the problems described here appear to be much more severe.
> 
> I'm using POV-Ray 3.7 on OpenSUSE 12.2.
> 

It is not related to 81, but 297

http://bugs.povray.org/task/297

(81 is about artefact (noise) in solver, whereas 297 is about epsilon)

A lot of shapes would not scale either. That's 297.

-- 
Just because nobody complains does not mean all parachutes are perfect.


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From: Roman
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 08:35:37
Message: <52ab0d29$1@news.povray.org>
On 2013-12-13 13:50, Le_Forgeron wrote:

> It is not related to 81, but 297
>
> http://bugs.povray.org/task/297
>
> (81 is about artefact (noise) in solver, whereas 297 is about epsilon)
>
> A lot of shapes would not scale either. That's 297.

Thank you for clarifying this. To work around the problem, I'm currently 
scaling my whole scene to a size that works for all objects. That's a 
bit cumbersome though, and I'm worried that such a common error-free 
scale won't exist in all cases. IMHO this is a serious limitation of 
POV-Ray that should be fixed, if at all possible.


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From: Fractracer
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 14:35:00
Message: <web.52ab608a49e06bf9989951cb0@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> I wonder if you can /scale/ a camera? In the docs section about
> transforming the camera, this is /not/ mentioned as such, only rotate
> and translate, so maybe there lies the problem.
>
> Thomas

Roman has discovered a new version of the word angle, using scale is the same
that using angle, I have just tried it with somme blob.


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From: Fractracer
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 14:45:00
Message: <web.52ab631f49e06bf9989951cb0@news.povray.org>
Roman <vet### [at] ethzch> wrote:
> On 2013-12-13 13:50, Le_Forgeron wrote:
>
> > It is not related to 81, but 297
> >
> > http://bugs.povray.org/task/297
> >
> > (81 is about artefact (noise) in solver, whereas 297 is about epsilon)
> >
> > A lot of shapes would not scale either. That's 297.
>
> Thank you for clarifying this. To work around the problem, I'm currently
> scaling my whole scene to a size that works for all objects. That's a
> bit cumbersome though, and I'm worried that such a common error-free
> scale won't exist in all cases. IMHO this is a serious limitation of
> POV-Ray that should be fixed, if at all possible.

I'm trying with low scale on sphere_sweep and it appears discontinuities when
approching a scale value of 0.005. Scaling the camera has no effect on the
sphere_sweep, it just act like angle.


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From: Fractracer
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 15:25:00
Message: <web.52ab6cd049e06bf9989951cb0@news.povray.org>
Le_Forgeron <lef### [at] freefr> wrote:
> Le 13/12/2013 11:55, Roman a écrit :
> > Hi there,
> >
> > The minimal scene file below should produce identical images for any
> > value of the scaling factor s, but it doesn't. s=1e-1 works fine, s=1e-3
> > produces individual spheres instead of a sweep, and s=1e-5 makes the
> > object fully invisible. The code for sphere_sweep doesn't seem to scale.
> >
> > Using other values for the sphere_sweep tolerance and turning off the
> > bounding (-MB) doesn't solve the problem.
> >
> > This might be related to http://bugs.povray.org/task/81, as I'm getting
> > the artifacts described there as well for intermediate scaling factors,
> > but the problems described here appear to be much more severe.
> >
> > I'm using POV-Ray 3.7 on OpenSUSE 12.2.
> >
>
> It is not related to 81, but 297
>
> http://bugs.povray.org/task/297
>
> (81 is about artefact (noise) in solver, whereas 297 is about epsilon)
>
> A lot of shapes would not scale either. That's 297.
>
> --

Me again! After some reading I think the problem is related to problem #243 for
pov3.7 and 92 for Pov3.6. A too little scale make artifacts. No solution with
SDL. I have tested the file *.pov from #243 with Pov3.6 and 3.7 and the two
differents artifacts appears.
I maybe will try with UberPov, but it is actually buzy in work.


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From: clipka
Subject: Re: sphere_sweep doesn't scale
Date: 13 Dec 2013 20:25:19
Message: <52abb37f$1@news.povray.org>
Am 13.12.2013 21:23, schrieb Fractracer:

> Me again! After some reading I think the problem is related to problem #243 for
> pov3.7 and 92 for Pov3.6. A too little scale make artifacts. No solution with
> SDL. I have tested the file *.pov from #243 with Pov3.6 and 3.7 and the two
> differents artifacts appears.
> I maybe will try with UberPov, but it is actually buzy in work.

Don't bother; UberPOV is no different than official POV-Ray 3.7.0 when 
it comes to sphere_sweep.


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From: Thomas de Groot
Subject: Re: sphere_sweep doesn't scale
Date: 14 Dec 2013 10:04:05
Message: <52ac7365$1@news.povray.org>
On 13-12-2013 20:31, Fractracer wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> I wonder if you can /scale/ a camera? In the docs section about
>> transforming the camera, this is /not/ mentioned as such, only rotate
>> and translate, so maybe there lies the problem.
>>
>> Thomas
>
> Roman has discovered a new version of the word angle, using scale is the same
> that using angle, I have just tried it with somme blob.
>
>

That is strange indeed. In my simple world view I would think that angle 
and scale are two very different processes. Even if both give identical 
results, I would like an explanation about how that comes to be.

Thomas


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From: Roman
Subject: Re: sphere_sweep doesn't scale
Date: 14 Dec 2013 13:40:44
Message: <52aca62c$1@news.povray.org>
On 2013-12-13 14:35, Roman wrote:

> Thank you for clarifying this. To work around the problem, I'm currently
> scaling my whole scene to a size that works for all objects. That's a
> bit cumbersome though, and I'm worried that such a common error-free
> scale won't exist in all cases. IMHO this is a serious limitation of
> POV-Ray that should be fixed, if at all possible.


I'm still struggling with this issue. So I've rescaled everything to a 
size that works for sphere_sweep, but now some of my other objects look 
wrong. More precisely, their materials look wrong. I have narrowed it 
down to the minimal scene file below, which shows a sphere with a 
non-zero filter value in the pigment. Different scales result in 
different images. What gives? I'm confused.

-Roman



// START MINIMAL SCENE FILE

#version 3.7;

// 1e-2, 1e-3, 1e-4, 1e-5 all produce different images,
// 1e-6 even produces a parse error!
#declare s = 1e-6;

camera { location 3*s*z look_at 0 }

light_source { s*<10,5,20>, rgb 1 }

sphere { 0, s pigment { color rgb <1,0,0> filter 0.5 } }

// END MINIMAL SCENE FILE


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Attachments:
Download 'scale_problem_1e-2.png' (3 KB) Download 'scale_problem_1e-3.png' (3 KB) Download 'scale_problem_1e-4.png' (3 KB) Download 'scale_problem_1e-5.png' (1 KB)

Preview of image 'scale_problem_1e-2.png'
scale_problem_1e-2.png

Preview of image 'scale_problem_1e-3.png'
scale_problem_1e-3.png

Preview of image 'scale_problem_1e-4.png'
scale_problem_1e-4.png

Preview of image 'scale_problem_1e-5.png'
scale_problem_1e-5.png


 

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