POV-Ray : Newsgroups : povray.bugreports : Something fishy with Julia_Fractal Server Time: 25 Jun 2019 20:27:14 GMT
  Something fishy with Julia_Fractal (Message 1 to 5 of 5)  
From: Sven Geier
Subject: Something fishy with Julia_Fractal
Date: 2 May 2011 22:25:00
Message: <web.4dbf2e26b56a53c15b4449250@news.povray.org>
In the following, note the parameter cam_distance, which merely scales the
distance of the camera from the origin (along the given vector). Paste this into
your POV-ray as-is and render it with the number in there (cam_distance=0.7)

Make a copy of the resulting image. Now change cam_distance to 0.5 and render
again. Compare with the previous image.

What I would expect to happen is that I'd see the object somewhat
closer-up (and thus lose some of it around the edges). Which does in fact
happen. However in addition the "ring" in the center of the object that was wide
open before closes in the front.

Surely a change in the shape of a rendered object with camera location would be
a bug, no?

# == POV-Ray file begins here
#version 3.7;

#include "functions.inc"
global_settings { assumed_gamma 2.2 }

#declare cam_distance = 0.7;

camera { angle 45
  location  <10, .5, 0> * cam_distance
  look_at   <0, 0,  -.5>
  right     x*640/400
  rotate <0,-5,0>
}

light_source { 0 color rgb 1 spotlight
  translate <80, 80, -40> point_at 0 }
light_source { 0 color rgb <2,1,0> translate <-20, 40, -20> }
sky_sphere { pigment { gradient -y }}

julia_fractal{ <-1.483,0,-0.0,-0.025>
   quaternion sqr max_iteration 12 precision 500
   texture{
     pigment{ color rgb 0.7}
     finish { phong .6 reflection {.6 metallic }}
   }
   scale 3
   rotate <0,110,-45>
}
# == POV-Ray file ends here


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From: Christian Froeschlin
Subject: Re: Something fishy with Julia_Fractal
Date: 3 May 2011 00:10:09
Message: <4dbf47e1@news.povray.org>
Sven Geier wrote:

> However in addition the "ring" in the center of the object that was wide
> open before closes in the front.

I can reproduce this with 3.7 RC 3 on Win64. It is probably some
sort of numerical issue (I think the ring should be closed and part
of it gets lost - rotating the object along its axis doesn't move
the gap). However, cranking up the precision or intervals doesn't
seems to restore ring so I also think this is a bit fishy.


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From: Sven Geier
Subject: Re: Something fishy with Julia_Fractal
Date: 5 May 2011 01:25:00
Message: <web.4dc1fc143d45d7de5b4449250@news.povray.org>
Christian Froeschlin <chr### [at] chrfrde> wrote:
> Sven Geier wrote:
>
> > However in addition the "ring" in the center of the object that was wide
> > open before closes in the front.
>
> I can reproduce this with 3.7 RC 3 on Win64.

Oh, sorry, yes I should have included that information, obviously:
3.7rc3, Windows server 2003, 32 bit, (1 gig ram, dual Xeon/dual core).


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From: Le Forgeron
Subject: Re: Something fishy with Julia_Fractal
Date: 7 May 2011 09:41:40
Message: <4dc513d4@news.povray.org>
Le 03/05/2011 00:21, Sven Geier nous fit lire :
> Surely a change in the shape of a rendered object with camera location would be
> a bug, no?

A bug report, yes.
A bug... in the actual case: nope.

The camera is inside the object bounding box, probably colliding with
the object.

The good news: it was the same with 3.6 too.
attached pictures from 3.7 & 3.6 (changed texture) for 0.5 and 0.59333
for cam_distance.

the camera plan is clipping the object.


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Attachments:
Download 'chang36.png' (84 KB)
Download 'chang36_05.png' (91 KB)
Download 'chang37.png' (82 KB)
Download 'chang37_05.png' (90 KB)

Preview of image 'chang36.png'
chang36.png

Preview of image 'chang36_05.png'
chang36_05.png

Preview of image 'chang37.png'
chang37.png

Preview of image 'chang37_05.png'
chang37_05.png


 

From: Sven Geier
Subject: Re: Something fishy with Julia_Fractal
Date: 9 May 2011 21:40:01
Message: <web.4dc85f0a3d45d7de5b4449250@news.povray.org>
Le_Forgeron <jgr### [at] freefr> wrote:
> Le 03/05/2011 00:21, Sven Geier nous fit lire :
> > Surely a change in the shape of a rendered object with camera location would be
> > a bug, no?
>
> A bug report, yes.
> A bug... in the actual case: nope.
>
> The camera is inside the object bounding box, probably colliding with
> the object.
>
> The good news: it was the same with 3.6 too.
> attached pictures from 3.7 & 3.6 (changed texture) for 0.5 and 0.59333
> for cam_distance.
>
> the camera plan is clipping the object.

So just to keep those in the loop that don't follow the bug tracker:

The ring opens when the camera is moved *away* from the object. The object looks
fine when the camera is very close.

This makes clipping a somewhat less likely explanation.


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