POV-Ray : Newsgroups : povray.bugreports : hidden plane issue Server Time: 19 Feb 2019 23:47:28 GMT
  hidden plane issue (Message 1 to 4 of 4)  
From: gnagflow
Subject: hidden plane issue
Date: 25 Jan 2019 11:15:01
Message: <web.5c4aef64f5975424497c656a0@news.povray.org>
Hi,
although hidden behind the red plane, parts of the blue plane can be seen
from the following location.

-------------- cut here ----------------------------
#version 3.7;

global_settings {
  assumed_gamma 1.0
}

camera {
  perspective
  location     -1 * <0, 1, 1/50000>
  direction     1 *  y
  look_at            y
}

light_source
{
    <0, -1, -1>
    color red 1.0  green 1.0  blue 1.0
}

plane { z, 0
  pigment{
    color rgb <1, 0, 0>
  }
}

plane { z, 1
  pigment{
    color rgb <0, 0, 1>
  }
  finish {
    ambient  1
    emission 0
  }
}
----------------------------------------------------

The effect was discovered on Linux kernel 4.20.2 with x86_64 GNU/Linux
architecture using POV-Ray 3.7.0.8.unofficial version but can pretty much be
reproduced on any system as far as I can tell. Accept my apologies if the
issue is already known, in which case I would be grateful for any further
hints regarding a remedy.

Regards
Wolfgang


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From: clipka
Subject: Re: hidden plane issue
Date: 25 Jan 2019 15:06:03
Message: <5c4b25db$1@news.povray.org>
Am 25.01.2019 um 12:13 schrieb gnagflow:
> Hi,
> although hidden behind the red plane, parts of the blue plane can be seen
> from the following location.

This is a simple precision issue: The camera does not "see" geometry 
that is too close to the camera's location (or, more precisely, the 
rays' origin). With the camera being very close to the red plane, a 
circular patch of it therefore disappears.

Increase the scale of your entire scene and you should be fine.


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From: William F Pokorny
Subject: Re: hidden plane issue
Date: 25 Jan 2019 15:35:14
Message: <5c4b2cb2@news.povray.org>
On 1/25/19 6:13 AM, gnagflow wrote:
> Hi,
> although hidden behind the red plane, parts of the blue plane can be seen
> from the following location.
> 
> -------------- cut here ----------------------------
> #version 3.7;
> 
> global_settings {
>    assumed_gamma 1.0
> }
> 
> camera {
>    perspective
>    location     -1 * <0, 1, 1/50000>
>    direction     1 *  y
>    look_at            y
> }
> 
> light_source
> {
>      <0, -1, -1>
>      color red 1.0  green 1.0  blue 1.0
> }
> 
> plane { z, 0
>    pigment{
>      color rgb <1, 0, 0>
>    }
> }
> 
> plane { z, 1
>    pigment{
>      color rgb <0, 0, 1>
>    }
>    finish {
>      ambient  1
>      emission 0
>    }
> }
> ----------------------------------------------------
> 
> The effect was discovered on Linux kernel 4.20.2 with x86_64 GNU/Linux
> architecture using POV-Ray 3.7.0.8.unofficial version but can pretty much be
> reproduced on any system as far as I can tell. Accept my apologies if the
> issue is already known, in which case I would be grateful for any further
> hints regarding a remedy.
> 
> Regards
> Wolfgang
> 
> 
> 
Looks to be related, by magnitude, mostly to the work going on for this 
pull request:

https://github.com/POV-Ray/povray/pull/358

and two or three similar open github issues - most/all? mentioned in the 
358 discussion thread as I recall.

In your case the first ray surface intersection is being ignored if it 
is closer than 1e-4. FYI. I'm adding your scene to my solver/tolerance 
testing scene collection.

The current - and near term - work around in your scene is to keep the 
camera more than 1e-4 off/outside the red plane's surface.

A better rule of thumb though is >1e-3 outside shapes / away from 
surfaces for lights, cameras and surface relationships - in the world 
scene space. In some scenes with the orthographic camera & user_defined 
cameras that might not be possible depending upon the scene. It's not 
enough for some shapes and scene set ups, but still a decent rule of 
thumb value.

My current, local, solver branch going after a set of related fixes 
renders only the red plane for what it's worth. That branch is an effort 
aimed at fixing/improving a largish set of accuracy issues to which this 
one (pull 358 et al) is somewhat related.

Bill P.


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From: gnagflow
Subject: Re: hidden plane issue
Date: 25 Jan 2019 15:45:00
Message: <web.5c4b2e7c12ed4887497c656a0@news.povray.org>
> This is a simple precision issue: The camera does not "see" geometry
> that is too close to the camera's location (or, more precisely, the
> rays' origin). With the camera being very close to the red plane, a
> circular patch of it therefore disappears.
>
> Increase the scale of your entire scene and you should be fine.

I was ray-tracing scenes close to the surface of the earth (but not too
close to be aproximated by a flat plane where curvature no longer matters).
Is there another way to increase the precision?

Thx


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