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Hmm just getting to an internet connection where I can read the
POV NGs after a few days...
on the way up to Illinois for vacation, the reference to
the experiment used to test whether light is particles or
waves struck me as being interesting.
Question: Are POV photons waves, or particles? (or neither) ;)
As I don't currently have access to POV 3.5 b, I must ask
y'all to try this for me.
Construct a photon-using scene as follows:
area wall w/1 slit in centre
light | | |
* | | | white screen
| | |
wall w/2 slits dividing wall into 3 equal parts
I predict the following possible outcomes of this render:
1) the white screen will not be illuminated at all
2) the white screen will have an interference pattern on it
3) the white screen will have two lines with fuzzy edges
4) the white screen will have two lines with sharp edges
Another question: is polarisation possible in POV?
- Tim Cook
http://empyrean.scifi-fantasy.com
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In article <3C408458.962543F1@scifi-fantasy.com>,
Tim Cook <tim### [at] scifi-fantasy com> wrote:
> Question: Are POV photons waves, or particles? (or neither) ;)
Particles. Simulating the wave nature would require huge amounts of
processing power...
> I predict the following possible outcomes of this render:
> 1) the white screen will not be illuminated at all
> 2) the white screen will have an interference pattern on it
> 3) the white screen will have two lines with fuzzy edges
> 4) the white screen will have two lines with sharp edges
Depending on the width of the first slit and distance of the light,
either 1 or something like 3, with the fuzzyness depending on the number
of photons you used.
> Another question: is polarisation possible in POV?
No.
POV-Ray is not designed for physically correct simulation of optical
effects, it took a long time just for dispersion and photon mapping to
be added. Effects like diffraction are often difficult to implement,
very slow to compute, and would contribute little or nothing to the
majority of scenes.
--
--
Christopher James Huff <chr### [at] maccom>
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http://www.winosi.onlinehome.de
Tim Cook wrote:
> Hmm just getting to an internet connection where I can read the
> POV NGs after a few days...
> on the way up to Illinois for vacation, the reference to
> the experiment used to test whether light is particles or
> waves struck me as being interesting.
>
> Question: Are POV photons waves, or particles? (or neither) ;)
>
> As I don't currently have access to POV 3.5 b, I must ask
> y'all to try this for me.
>
> Construct a photon-using scene as follows:
>
> area wall w/1 slit in centre
> light | | |
> * | | | white screen
> | | |
> wall w/2 slits dividing wall into 3 equal parts
>
> I predict the following possible outcomes of this render:
> 1) the white screen will not be illuminated at all
> 2) the white screen will have an interference pattern on it
> 3) the white screen will have two lines with fuzzy edges
> 4) the white screen will have two lines with sharp edges
>
> Another question: is polarisation possible in POV?
>
> - Tim Cook
> http://empyrean.scifi-fantasy.com
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On Sat, 12 Jan 2002 16:17:00 -0500, Christopher James Huff wrote:
> POV-Ray is not designed for physically correct simulation of optical
> effects, it took a long time just for dispersion and photon mapping to
> be added. Effects like diffraction are often difficult to implement,
> very slow to compute, and would contribute little or nothing to the
> majority of scenes.
Polarization wouldn't be much harder to deal with than dispersion, though
birefringence might make it a little more interesting.
Note, too, that dispersion isn't perfect either. For one thing, it
assumes that the function relating IOR to wavelength is very simple
for the visible spectrum. For another, since it's being forced to
work with tristimulus values (RGB) instead of spectral power distributions,
it has to infer some sort of tristimulus->SPD conversion where none
exists. If we provided a way to specify colors as SPDs this wouldn't
be such an issue, of course, but we haven't done that. (For more on
tristimulus values, SPDs, and the pitfalls of conversion, check out
the Color FAQ at http://www.inforamp.net/~poynton/PDFs/ColorFAQ.pdf )
Daren Wilson's original dispersion patch had some support for something
approaching SPDs in the form of 12-component colors, but that support
didn't make it into 3.5. On the other hand, his RGB->SPD conversion was
much less realistic than the one I threw together for 3.5, so hopefully
users will feel that it's balanced out at least a little.
--
#macro R(L P)sphere{L __}cylinder{L P __}#end#macro P(_1)union{R(z+_ z)R(-z _-z)
R(_-z*3_+z)torus{1__ clipped_by{plane{_ 0}}}translate z+_1}#end#macro S(_)9-(_1-
_)*(_1-_)#end#macro Z(_1 _ __)union{P(_)P(-_)R(y-z-1_)translate.1*_1-y*8pigment{
rgb<S(7)S(5)S(3)>}}#if(_1)Z(_1-__,_,__)#end#end Z(10x*-2,.2)camera{rotate x*90}
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In article <slr### [at] fwicom>,
Ron Parker <ron### [at] povrayorg> wrote:
> Polarization wouldn't be much harder to deal with than dispersion, though
> birefringence might make it a little more interesting.
Wouldn't you have to keep track of the amount of light polarized along
each plane? Probably with some kind of spline relating intensity of
light to angle of polarization? A lot more data for each ray...
--
--
Christopher James Huff <chr### [at] maccom>
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On Mon, 14 Jan 2002 13:41:47 -0500, Christopher James Huff wrote:
> In article <slr### [at] fwicom>,
> Ron Parker <ron### [at] povrayorg> wrote:
>
>> Polarization wouldn't be much harder to deal with than dispersion, though
>> birefringence might make it a little more interesting.
>
> Wouldn't you have to keep track of the amount of light polarized along
> each plane? Probably with some kind of spline relating intensity of
> light to angle of polarization? A lot more data for each ray...
Compared to what we keep track of for dispersion? Not really.
--
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}
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Ron Parker wrote:
> Christopher James Huff wrote:
> > Wouldn't you have to keep track of the amount of light polarized
> > along each plane? Probably with some kind of spline relating
> > intensity of light to angle of polarization? A lot more data
> > for each ray...
> Compared to what we keep track of for dispersion? Not really.
There's only 3 more values per ray for a more realistic simulation
of light; amplidude/frequency/rotation around axis of travel...?
Could probably do some interesting things with having materials
change the frequency of the light...
Speaking of something completely different...iridescence. It's
an interference pattern between two surfaces of oil or similar,
how 'bout trying to do that the hard way in POV? Should be
doable even in 3.1g...I think I'll play around with that and
such when I get back to my computer.
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In article <3C49E792.62CAB2DC@scifi-fantasy.com>,
Tim Cook <tim### [at] scifi-fantasycom> wrote:
> There's only 3 more values per ray for a more realistic simulation
> of light; amplidude/frequency/rotation around axis of travel...?
I think you would have to store more information, a bunch of "samples"
around the axis of travel, interpolated with a spline if the
calculations need it. Ordinary light isn't polarized in a single
direction, it is a mix of photons polarized in all directions.
Frequency has more to do with color, and is a different issue. POV could
assume all photons are in the same frequency range independant of
polarization, and just store weight values specifying the percentage
polarized at each angle. The more samples, the better the accuracy, but
slower and using more memory.
> Speaking of something completely different...iridescence. It's
> an interference pattern between two surfaces of oil or similar,
> how 'bout trying to do that the hard way in POV? Should be
> doable even in 3.1g...I think I'll play around with that and
> such when I get back to my computer.
There is the "irid" finish feature, which is apparently somewhat based
on reality, though not a physical simulation...
I don't know what you have in mind though...simulating the waveforms
with the onion pattern?
--
--
Christopher James Huff <chr### [at] maccom>
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Christopher James Huff wrote:
> There is the "irid" finish feature, which is apparently somewhat
> based on reality, though not a physical simulation...
> I don't know what you have in mind though...simulating the waveforms
> with the onion pattern?
That or something similar...make two layers of patterned materials
close to each other but slightly misaligned...I've already managed
to achieve anisotropic reflection by actually modelling the finish,
so I wonder what other 'effects' I can do straight cheap-simulation
of.
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In article <3C49ED2D.E6961A0E@scifi-fantasy.com>,
Tim Cook <tim### [at] scifi-fantasycom> wrote:
> That or something similar...make two layers of patterned materials
> close to each other but slightly misaligned...
> I've already managed to achieve anisotropic reflection by actually
> modelling the finish, so I wonder what other 'effects' I can do
> straight cheap-simulation of.
Details? I've done it by using averaged textures (I think Ron Parker
discovered this technique), with each texture identical except for the
normal...and a slower, older method used a very finely scaled normal and
high antialiasing.
--
--
Christopher James Huff <chr### [at] maccom>
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