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  truncated spheres (Message 1 to 6 of 6)  
From: dragonmage
Subject: truncated spheres
Date: 20 Mar 2007 20:25:03
Message: <web.4600885280e10529add0a3280@news.povray.org>
Hi, I have been testing the effects of translating a scene (including
viewpoints and lights in the local scene) away from the origin.

When I get to around 1million units, spheres get truncated in a strange way:
they are drawn either hemispherical or quarter spherical. Looking at
Spheres.cpp gives me no clue as to the cause - nothing obvious.

The truncation is not z buffer clipping or due to other objects in the scene
(a plane) as far as I can determine. I suspect that the displacement is
introducing enough error into the program that some part of the
calculations do not render some quarters of the spheres.

Anyone have insight into the actual part of the calculation that is failing?

Image and pov file are here:

http://www.planet-earth.org/SpheresStressTest1Mil.pov
http://www.planet-earth.org/SpheresStressTest1Mil.jpg


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From: Chambers
Subject: Re: truncated spheres
Date: 20 Mar 2007 20:40:38
Message: <46008d16@news.povray.org>
dragonmage wrote:
> Hi, I have been testing the effects of translating a scene (including
> viewpoints and lights in the local scene) away from the origin.

Your question has been answered by a couple of people in the Advanced 
group, where you originally posted.

...Chambers


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From: dragonmage
Subject: Re: truncated spheres
Date: 20 Mar 2007 21:30:02
Message: <web.460097c842d0a127add0a3280@news.povray.org>
Chambers <ben### [at] pacificwebguycom> wrote:
> dragonmage wrote:
> > Hi, I have been testing the effects of translating a scene (including
> > viewpoints and lights in the local scene) away from the origin.
>
> Your question has been answered by a couple of people in the Advanced
> group, where you originally posted.
>
> ...Chambers

No - they were all guesses, and some were contradicted by others.
This group looks more appropriate for questions on code so I posted here.

chris


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From: Chambers
Subject: Re: truncated spheres
Date: 20 Mar 2007 23:05:35
Message: <4600af0f@news.povray.org>
dragonmage wrote:
> No - they were all guesses, and some were contradicted by others.
> This group looks more appropriate for questions on code so I posted here.

Thorsten is one of the main developers of POV-Ray, so you should trust 
his answer.  My answer was a guess, of course.

...Chambers


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From: dragonmage
Subject: Re: truncated spheres
Date: 20 Mar 2007 23:30:02
Message: <web.4600b3bb42d0a127add0a3280@news.povray.org>
Chambers <ben### [at] pacificwebguycom> wrote:
> dragonmage wrote:
> > No - they were all guesses, and some were contradicted by others.
> > This group looks more appropriate for questions on code so I posted here.
>
> Thorsten is one of the main developers of POV-Ray, so you should trust
> his answer.  My answer was a guess, of course.
>
> ...Chambers


Well I apologise if I offended anyone - no offence intended.
I didn't see a "Thorsten" on the truncated spheres thread.
I don't question ppls experience/knowledge but there has been no
definitive answer so far.

What *I* know is that the cause is the low resolution of space in the region
the scene was transported to.

What I would like to understand is how the sphere rendering was specifically
affected. It appears to affect parts of the spheres in quadrants with neat
180 degree or 90degree "slices", not random clipping or tearing. But it is
probably unreasonable to expect someone to know offhand - I just hoped
someone would have insight into this.

chris


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From: dragonmage
Subject: Re: truncated spheres
Date: 21 Mar 2007 00:15:01
Message: <web.4600befe42d0a127add0a3280@news.povray.org>
"dragonmage" <dra### [at] gmailcom> wrote:
> Chambers <ben### [at] pacificwebguycom> wrote:
> > dragonmage wrote:
> > > No - they were all guesses, and some were contradicted by others.
> > > This group looks more appropriate for questions on code so I posted here.
> >
> > Thorsten is one of the main developers of POV-Ray, so you should trust
> > his answer.  My answer was a guess, of course.
> >
> > ...Chambers
>
>
> Well I apologise if I offended anyone - no offence intended.
> I didn't see a "Thorsten" on the truncated spheres thread.

Ah - just found his msg. Sent a response,

thx,

chris


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