hello,

30 minutes ago I started looking at the parametric object, and the result
was a bit strange (and slow). I used the piece of code from the help files
to make a sphere, and then changed it to make a half sphere and gave it a
"pigment{White}". I was expecting to see a white half sphere, but what I
saw, was a blackish/grey-ish kind of shape.
This puzzeled me. So I made added a half white hollow sphere to the scene,
to show you (the newsgroup) wat I was expecting, and what I was getting.
But then it even became more puzzling. There were now 2
half-white-hollow-spheres!

Does anyone know what is happening here?

The source will be posted in p.b.sf

Thanks in advance,

JWV

Post a reply to this message

In article <410946f3$1@news.povray.org> , "JWV" <jwv|at|planet.nl> wrote:

> There were now 2
> half-white-hollow-spheres!

Maybe you are seeing a shadow inside the hollow part of the half sphere?

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message

Wasn't it JWV who wrote:
>hello,
>
>30 minutes ago I started looking at the parametric object, and the result
>was a bit strange (and slow). I used the piece of code from the help files
>to make a sphere, and then changed it to make a half sphere and gave it a
>"pigment{White}". I was expecting to see a white half sphere, but what I
>saw, was a blackish/grey-ish kind of shape.
>This puzzeled me. So I made added a half white hollow sphere to the scene,
>to show you (the newsgroup) wat I was expecting, and what I was getting.
>But then it even became more puzzling. There were now 2
>half-white-hollow-spheres!
>
>Does anyone know what is happening here?
>
>The source will be posted in p.b.sf

It looks like it might be a bounding bug, and may have something to do
with shadow testing.

The default Bounding Threshold is 3. [When there are only a few objects
in a scene, the overheads involved in performing bounding tests are
often not worth while, so POV doesn't perform bounding when there are
less than this number of objects present.]

When there were only two objects in your scene (the parametric object
and the plane) bounding was disabled. Adding any third object caused the
bounding code to be activated. [You can force bounding to activate by
setting the Bounding Threshold to 0 with +MB0 in the command line.]

There are other weird things going on. Changing your "contained_by" to a
box causes the parametric to render correctly.

I suspect the shadow testing code, since some of my isosurface tutorial
examples have less than three objects in the scene and seem to render
correctly (I'll check them all properly under 3.6 tomorrow). The thing
that causes the difference in my example scenes is that my parametric
examples have "no_shadow".

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message

"JWV" <jwv|at|planet.nl> wrote:

> Does anyone know what is happening here?
> 
Yes. You are experiencing the long-known parametric object bug. 
I have a patch on my homepage (which was not included into POV-3.6): 
http://www.cip.physik.uni-muenchen.de/~wwieser/render/povray/patches/
(Its part of the "combined bugfix patch".)

With the patch applied, the image looks like the one posted in 
p.b.images "Re: question about parametric object". 

Wolfgang

Post a reply to this message

JWV wrote:
>> hello,
>>
>> 30 minutes ago I started looking at the parametric object, and the
>> result was a bit strange (and slow). I used the piece of code from
>> the help files to make a sphere, and then changed it to make a half
>> sphere and gave it a "pigment{White}". I was expecting to see a
>> white half sphere, but what I saw, was a blackish/grey-ish kind of
>> shape.
>> This puzzeled me. So I made added a half white hollow sphere to the
>> scene, to show you (the newsgroup) wat I was expecting, and what I
>> was getting. But then it even became more puzzling. There were now 2
>> half-white-hollow-spheres!
>>
>> Does anyone know what is happening here?
>>
>> The source will be posted in p.b.sf
>>
>> Thanks in advance,
>>
>> JWV

I got the same result. But adding

global_settings {  assumed_gamma 1.0 }

to the SDF gave better results.

Post a reply to this message

Hi Mike,

Adding +MB0 helped, thanks for the explaination!

Greetz,

JWV

"Mike Williams" <nos### [at] econymdemoncouk> wrote in message
news:xQW### [at] econymdemoncouk...
> Wasn't it JWV who wrote:
> >hello,
> >
> >30 minutes ago I started looking at the parametric object, and the result
> >was a bit strange (and slow). I used the piece of code from the help
files
> >to make a sphere, and then changed it to make a half sphere and gave it a
> >"pigment{White}". I was expecting to see a white half sphere, but what I
> >saw, was a blackish/grey-ish kind of shape.
> >This puzzeled me. So I made added a half white hollow sphere to the
scene,
> >to show you (the newsgroup) wat I was expecting, and what I was getting.
> >But then it even became more puzzling. There were now 2
> >half-white-hollow-spheres!
> >
> >Does anyone know what is happening here?
> >
> >The source will be posted in p.b.sf
>
> It looks like it might be a bounding bug, and may have something to do
> with shadow testing.
>
> The default Bounding Threshold is 3. [When there are only a few objects
> in a scene, the overheads involved in performing bounding tests are
> often not worth while, so POV doesn't perform bounding when there are
> less than this number of objects present.]
>
> When there were only two objects in your scene (the parametric object
> and the plane) bounding was disabled. Adding any third object caused the
> bounding code to be activated. [You can force bounding to activate by
> setting the Bounding Threshold to 0 with +MB0 in the command line.]
>
> There are other weird things going on. Changing your "contained_by" to a
> box causes the parametric to render correctly.
>
> I suspect the shadow testing code, since some of my isosurface tutorial
> examples have less than three objects in the scene and seem to render
> correctly (I'll check them all properly under 3.6 tomorrow). The thing
> that causes the difference in my example scenes is that my parametric
> examples have "no_shadow".
>
> -- 
> Mike Williams
> Gentleman of Leisure

Post a reply to this message

Thanks for pointing me to your website, but since Mike's tip helped me for
the moment, i will not use your patch at this point (no offense :-)).
But i will have a look at the grid pattern patch you made, it looks rather
helpfull :-).

Greetings,

JWV

"Wolfgang Wieser" <wwi### [at] nospamgmxde> wrote in message
news:4109f01d@news.povray.org...
> "JWV" <jwv|at|planet.nl> wrote:
>
> > Does anyone know what is happening here?
> >
> Yes. You are experiencing the long-known parametric object bug.
> I have a patch on my homepage (which was not included into POV-3.6):
> http://www.cip.physik.uni-muenchen.de/~wwieser/render/povray/patches/
> (Its part of the "combined bugfix patch".)
>
> With the patch applied, the image looks like the one posted in
> p.b.images "Re: question about parametric object".
>
> Wolfgang
>

Post a reply to this message

Hi,

Thanks to all of you for the replies!

I have made my first image with a parametric object in it, it will be posted
in the straw topic.

Greetings,

JWV

"JWV" <jwv|at|planet.nl> wrote in message news:410946f3$1@news.povray.org...
> hello,
>
> 30 minutes ago I started looking at the parametric object, and the result
> was a bit strange (and slow). I used the piece of code from the help files
> to make a sphere, and then changed it to make a half sphere and gave it a
> "pigment{White}". I was expecting to see a white half sphere, but what I
> saw, was a blackish/grey-ish kind of shape.
> This puzzeled me. So I made added a half white hollow sphere to the scene,
> to show you (the newsgroup) wat I was expecting, and what I was getting.
> But then it even became more puzzling. There were now 2
> half-white-hollow-spheres!
>
> Does anyone know what is happening here?
>
> The source will be posted in p.b.sf
>
> Thanks in advance,
>
> JWV
>
>

Post a reply to this message