> Could be very well, though, that your problem has a completely different
>    source.

Another trouble could be that the normals don't point to the same side of
the triangle. I recall lighting issues when some of the normals of the
triangle were calculated clockwise and some counterclockwise when generating
them using my MMM with a faulty code.

Additionally, what's the size of your triangles? If they're *very* tiny, you
could run into the floating-point precision problem.

Regards,
Tim

-- 
aka "Tim Nikias v2.0"
Homepage: <http://www.nolights.de>

Post a reply to this message

thanks firstly,

i construct the mesh with marching cube algorithm based on a regular grid,
and the resolution of my grid is 80X40X100.

i check the online help of pov-ray, and it says: Typically values whose
absolute values are less than a preset value epsilon are considered false
for logical expressions. The value of epsilon is system dependent but is
generally about 1.0e-10. Two floats a and b are considered to be equal if
abs(a-b) < epsilon.

so maybe i should save my mesh file with double type, am going to try it,:)


"Tim Nikias" <JUSTTHELOWERCASE:timISNOTnikias(at)gmx.netWARE> wrote:
> > Could be very well, though, that your problem has a completely different
> >    source.
>
> Another trouble could be that the normals don't point to the same side of
> the triangle. I recall lighting issues when some of the normals of the
> triangle were calculated clockwise and some counterclockwise when generating
> them using my MMM with a faulty code.
>
> Additionally, what's the size of your triangles? If they're *very* tiny, you
> could run into the floating-point precision problem.
>
> Regards,
> Tim
>
> --
> aka "Tim Nikias v2.0"
> Homepage: <http://www.nolights.de>

Post a reply to this message

yes, a simulation

"Marc Jacquier" <jac### [at] wanadoofr> wrote:

> news:web.441fa27ddfe6af01598059850@news.povray.org...
> As sayd Florian, try rising max_trace_level
>
> BTW where did you get your mesh? a simulation?
>
> Marc

Post a reply to this message

thanks, good idea, i'll try~,


zorglub <zor### [at] e-garfieldcom> wrote:

> > i got a trianglar mesh file, and i render it with the "mesh2" object, the
> > result can be seen in the attachment. But there so many black holes in the
> > image.
>
> Try "max_trace_level" like the others says.
> And probably add "double_illuminate" ?
> In POV-Help it says :
> "A surface has two sides; usually, only the side facing the light source
> is illuminated, the other side remains in shadow. When double_illuminate
> is used, the other side is also illuminated.
> This is useful for simulating effects like translucency (as in a lamp
> shade, sheet of paper, etc)."

Post a reply to this message

"lien0n" <nomail@nomail> wrote:
> i got a trianglar mesh file, and i render it with the "mesh2" object, the
> result can be seen in the attachment. But there so many black holes in the
> image.

Just a guess, but could it have something to do with your REFLECTION values?
You have reflection {0.0, 1.0} as the min and max values.  The POV docs say,
"The minimum value is how reflective the surface will be when viewed from a
direction parallel to its normal..."  Here, the min value is 0...meaning
black (?) or no light reflection at all (?). Again, I'm just guessing, as I
haven't had occasion to use "minimum reflection" before, so I don't really
know *how* it works.

Ken

Post a reply to this message

i turned it to 0.5, and the result is much better~
 :)

"Kenneth" <kdw### [at] earthlinknet> wrote:
> "lien0n" <nomail@nomail> wrote:
> > i got a trianglar mesh file, and i render it with the "mesh2" object, the
> > result can be seen in the attachment. But there so many black holes in the
> > image.
>
> Just a guess, but could it have something to do with your REFLECTION values?
> You have reflection {0.0, 1.0} as the min and max values.  The POV docs say,
> "The minimum value is how reflective the surface will be when viewed from a
> direction parallel to its normal..."  Here, the min value is 0...meaning
> black (?) or no light reflection at all (?). Again, I'm just guessing, as I
> haven't had occasion to use "minimum reflection" before, so I don't really
> know *how* it works.
>
> Ken

Post a reply to this message

> i check the online help of pov-ray, and it says: Typically values whose
> absolute values are less than a preset value epsilon are considered false
> for logical expressions. The value of epsilon is system dependent but is
> generally about 1.0e-10. Two floats a and b are considered to be equal if
> abs(a-b) < epsilon.
>
> so maybe i should save my mesh file with double type, am going to try
it,:)

That's not what I meant. But if you lose very low floating-point values,
like the online help says, things will be considered equal and triangles
might get dropped. It sometimes help to multiply all numbers with 10, 100 or
1000 (depending on the small scale of the mesh) when exporting it, and try
scaling it down (though you could still run into the same problems).

All that aside, there's still the issue of max_trace_level and
reflection/refraction to be considered, you easily get black dots on
transparent objects that are a little more irregular than a sphere...

Regards,
Tim

-- 
aka "Tim Nikias v2.0"
Homepage: <http://www.nolights.de>

Post a reply to this message

but i also tried others' idea for changing the max_trace_level to be 20, and
the result appears excellent, though the render speed is slow, and am going
to seek for appropriate values for the max_trace_level and min reflection.

thanks, everyone, your ideas are so helpful~~~~,

"lien0n" <nomail@nomail> wrote:
> i turned it to 0.5, and the result is much better~
>  :)
>
> "Kenneth" <kdw### [at] earthlinknet> wrote:
> > "lien0n" <nomail@nomail> wrote:
> > > i got a trianglar mesh file, and i render it with the "mesh2" object, the
> > > result can be seen in the attachment. But there so many black holes in the
> > > image.
> >
> > Just a guess, but could it have something to do with your REFLECTION values?
> > You have reflection {0.0, 1.0} as the min and max values.  The POV docs say,
> > "The minimum value is how reflective the surface will be when viewed from a
> > direction parallel to its normal..."  Here, the min value is 0...meaning
> > black (?) or no light reflection at all (?). Again, I'm just guessing, as I
> > haven't had occasion to use "minimum reflection" before, so I don't really
> > know *how* it works.
> >
> > Ken

Post a reply to this message

news:web.44210cddb0f87641598059850@news.povray.org...
> but i also tried others' idea for changing the max_trace_level to be 20,
and
> the result appears excellent, though the render speed is slow, and am
going
> to seek for appropriate values for the max_trace_level and min reflection.


In addition to max_trace_level, you could want to tweak adc_bailout, I
suggest you have a look at the doc on this topic
I quote
"The point at which a ray's contribution is considered insignificant is
controlled by the adc_bailout value. The default is 1/255 or approximately
0.0039 since a change smaller than that could not be visible in a 24 bit
image. Generally this setting is perfectly adequate and should be left
alone. Setting adc_bailout to 0 will disable ADC, relying completely on
max_trace_level to set an upper limit on the number of rays spawned."

you could rise  adc_bailout to get shorter render times

Marc

Post a reply to this message

Hi,

> in my mesh file, there are three data blocks: vertices, normals, and
> triangles' vertex indices. I am sure that the vertices and the trianlges'

Just a thought: how about taking one vertice from every triangle and 
making a small blob from it? this way all the water should be much 
smoother than made from triangles... Never tried it before though.

cheers
-- 
Piotr "utak3r" Borys

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