Hi everyone,
  I have a source code with three quadrics that behave strangely: when I put
only two of the three quadrics, everything looks like it should, but when I
render with the three of them, one is strangely clipped off.
  Here is the code:

// --- code begin --- //

#declare Tex = texture {
  pigment {rgbt <.6,.6,.6,.8>}
  finish {ambient .3 diffuse .7}
}

#declare nappe0 = quadric
  {<2,-1,2><0,0,0><0,0,0> 0
  clipped_by{box{<10,2,10><-10,-2,-10>}}

  texture {Tex}
  }

#declare nappe1 = quadric
  {<2,-1,2><0,0,0><0,0,0> 3
  clipped_by{box{<10,2.3,10><-10,-2.3,-10>}}

  texture {Tex}
  }

#declare nappe2 = quadric
  {<2,-1,2><0,0,0><0,0,0> 0-3
  clipped_by{box {<10,1.7,10><-10,-1.7,-10>}}

  texture {Tex}
  }

object{nappe0}
object{nappe1}
object{nappe2}

camera {location <0,6,-8> look_at <0,1.1,0>}
background {color rgb 1}
global_settings {max_trace_level 12}
light_source {<4,8,-8> rgb 1}

// --- code end --- //

  Does any of you have an idea of what is going on ?
  I use povray 3.6 on a mandrake 10.1, and when I rendered (almost) the same
image some month ago with the version of povray 3.1 compiled by mandrake,
the problem didn't showed up.
  Last point: the problem disappears if I replace nappe2 by an isosurface
having exactly the same equation.

--

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>
>
>Hi everyone,
>  I have a source code with three quadrics that behave strangely: when I put
>only two of the three quadrics, everything looks like it should, but when I
>render with the three of them, one is strangely clipped off.
>
>  Does any of you have an idea of what is going on ?

I can't reproduce the problem (POV 3.6.0.icl8.win32) but situations
where things work correctly with two objects but bits disappear when
there are three objects tends to be caused by bugs in the automatic
bounding calculations. The bounding slab doesn't properly contain the
affected object.

The default Bounding_Threshold is 3. This means that automatic bounding
is switched off when rendering scenes with less than 3 objects. 

You can verify that this is the problem by rendering the image with a
higher Bounding_Threshold, by using +MB4 in the command line, and
observing that the image then renders correctly.

That's not a good solution, because you really don't want to disable
bounding in a large complex scene, but it gives a good basis for a bug
report.

-- 
Mike Williams
Gentleman of Leisure

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Mike Williams <nos### [at] econymdemoncouk> wrote:
>
> I can't reproduce the problem (POV 3.6.0.icl8.win32)

  I'm running POV 3.6.1 (g++ 3.4.1 @ i686-pc-linux-gnu).

> You can verify that this is the problem by rendering the image with a
> higher Bounding_Threshold, by using +MB4 in the command line, and
> observing that the image then renders correctly.

  You're right, with the +MB4 option the problem disappears.

> That's not a good solution, because you really don't want to disable
> bounding in a large complex scene, but it gives a good basis for a bug
> report.

  Ok, what's the next step? See if other people with 3.6.1 can reproduce the
problem ?

--

Post a reply to this message

>   I have a source code with three quadrics that behave strangely: when I put
> only two of the three quadrics, everything looks like it should, but when I
> render with the three of them, one is strangely clipped off.

I can confirm this over here (Gentoo Linux 2.6.11, Athlon XP 2600, 1 Gig 
Ram, POV-Ray official 3.6.1). The problem does not arise when using 
+MB4, as Mike suggested, so I, too, guess that it's a bounding issue.


HTH,
Florian

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Benoit Kloeckner wrote:
> Mike Williams <nos### [at] econymdemoncouk> wrote:
> 
>>I can't reproduce the problem (POV 3.6.0.icl8.win32)
> 
> 
>   I'm running POV 3.6.1 (g++ 3.4.1 @ i686-pc-linux-gnu).
> 
> 
>>You can verify that this is the problem by rendering the image with a
>>higher Bounding_Threshold, by using +MB4 in the command line, and
>>observing that the image then renders correctly.
> 
> 
>   You're right, with the +MB4 option the problem disappears.
> 
> 
>>That's not a good solution, because you really don't want to disable
>>bounding in a large complex scene, but it gives a good basis for a bug
>>report.
> 
> 
>   Ok, what's the next step? See if other people with 3.6.1 can reproduce the
> problem ?
> 
> --
> Benoit Kloeckner
> 
> 

	Manual bounding is possible in povray and will often
fix problems of this nature.
	For the problem object(s), manually specify a bounding
sphere or a bounding box.  The syntax is something like:

  quadric {
    .... snip ....
    bounded_by {
      sphere <0, 0, 0>, 1
    }
  }

	Manual bounding is ignored by povray unless you have the
right settting in your povray.ini file.  Something
like the following:

  Remove_Bounds=Off

	For some reason that never works so I've also added this
line to my povray.ini

  -UR

	That works for me.  See if that helps.  If not, then I am
at a loss for further ideas.


-- 
to all the companies who wait until a large user base becomes
dependant on their freeware, then shafting said happy campers with
mandatory payment for continued usage. I spit on your grave.

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