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I was inspired by a post of a few days ago. The question had to do
with modeling simulating the glow effect of optical fibers, which Bob
Hughes suggested might be done with radiosity and media.
My idea, however, goes a bit further. Optical fibers do glow when
light is passed through them, but they still emit a strongly directional
light from the end. (The glow, incidently is the color of the light
being passed through the strand)
As I understand it, this is because the fibers are coated with a
polymer that retains the ambient light with a minimum of loss, while
protecting the strand from damage due to handling.
So my question is: Is there an eficient way to model Optical fibers,
so that they not only glow, but transmit the light along the length as well.
Naturally, I'll continue my own experimentations. I would however
appreciate any thoughts people might have on the subject.
Regards,
A.D.B.
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Anthony D. Baye wrote:
>
> So my question is: Is there an eficient way to model Optical
> fibers, so that they not only glow, but transmit the light along the
> length as well.
> Naturally, I'll continue my own experimentations. I would however
> appreciate any thoughts people might have on the subject.
The transmission of light is nothing that makes sense to simulate in
POV-Ray since it has no effect on the image POV-Ray renders (light
itself isn't visible). Therefore using emitting media for the glow and
placing a spotlight at the end is the way to go.
Christoph
--
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 24 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/
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"Christoph Hormann" <chr### [at] gmx de> wrote in message
news:dcn984$3f2$1@chho.imagico.de...
> The transmission of light is nothing that makes sense to simulate in
> POV-Ray since it has no effect on the image POV-Ray renders (light itself
> isn't visible). Therefore using emitting media for the glow and placing a
> spotlight at the end is the way to go.
I don't think I can debate you on that, especially since I'm not sure what
you meant by "no effect on the image", but never say never. Not sure what
all Anthony knows about fiber optics but I know only enough to describe it
to people with no knowledge of it in the first place. ;)
As I might have said elsewhere already, I was once able to get a simulated
fiber optic cable made in POV and at least partially succeeded (maybe). It
was done by using photons and reflection on the inside of an S-shaped
sphere_sweep. I think it is total internal reflection effect, I believe,
that is the operative factor IRL. Meaning, the boundary of the tube with the
air is supposed to cause the light to stay within the tube walls because of
a specific limiting angle whereby light only reflects instead of breaks
through.
My test scene wasn't very good for anything as I recall, and I was counting
on faking it with reflection, not refraction. I'm not good enough with
photons to be sure if it really works or not anyway. I guess there would be
trouble due to how the photons are designed to map out into the scene, not
very sure of anything about it though. Probably was never designed to bounce
around inside of curving tubes.
Sure hope you can manage to do something with your idea, Anthony. I just
found the test scene I had done and rendered it as-is. Only got a bunch of
red spots everywhere, mostly at the ground beyond the opposite end of the
tube. Probably wouldn't help to see the scene yourself, it's basically just
a narrow spotlight close to one end of that sphere_sweep (hollowed out with
a smaller twin), which then has refraction and reflection including
interior_texture.
I just looked for info about TIR and fiber optics and there's mention of
critical angles for the light entering the tube and the bends in the tube.
Gets beyond me but this one web page allows for calculating the critical
incidence angle for different ior, if you're interested.
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html
Bob
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Bob Hughes wrote:
>
>>The transmission of light is nothing that makes sense to simulate in
>>POV-Ray since it has no effect on the image POV-Ray renders (light itself
>>isn't visible). Therefore using emitting media for the glow and placing a
>>spotlight at the end is the way to go.
>
>
> I don't think I can debate you on that, especially since I'm not sure what
> you meant by "no effect on the image", but never say never.
Sure. What i meant is that what you see of an optical fibre is the
light coming out at the end and the light scattered in the fibre. You
don't see the actual light transmitted.
> As I might have said elsewhere already, I was once able to get a simulated
> fiber optic cable made in POV and at least partially succeeded (maybe). It
> was done by using photons and reflection on the inside of an S-shaped
> sphere_sweep. I think it is total internal reflection effect, I believe,
> that is the operative factor IRL.
True optical fibres used for technical applications (data transmission)
have a non-constant IOR - light travels on curved path in those. What
you do with media and photons might actually lead to useable results in
a small test case but will be very slow and requires insane
max_trace_level for a larger setup.
Christoph
--
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 24 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/
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Christoph Hormann <chr### [at] gmxde> wrote:
> Bob Hughes wrote:
> >
> >
> > I don't think I can debate you on that, especially since I'm not sure what
> > you meant by "no effect on the image", but never say never.
>
> Sure. What i meant is that what you see of an optical fibre is the
> light coming out at the end and the light scattered in the fibre. You
> don't see the actual light transmitted.
>
To put it an other way. The Pov camera is not like a real life camera, it
does not register direct lighting. If you shine a light directly into a
camera with no other object in the scene you will get a black image.
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Christoph Hormann wrote:
> Anthony D. Baye wrote:
>
>>
>> So my question is: Is there an eficient way to model Optical
>> fibers, so that they not only glow, but transmit the light along the
>> length as well.
>> Naturally, I'll continue my own experimentations. I would however
>> appreciate any thoughts people might have on the subject.
>
>
> The transmission of light is nothing that makes sense to simulate in
> POV-Ray since it has no effect on the image POV-Ray renders (light
> itself isn't visible). Therefore using emitting media for the glow and
> placing a spotlight at the end is the way to go.
>
> Christoph
>
Hey Christoph,
Thanks for the input. The only problem that I see with your solution
is that, if I were trying to model one of those fiber optic displays
(f/ex. The flowers with the FO strands in them) I would have hundreds of
spotlights in my scene. The light calculations would take forever.
Now I'll admit that what I'm trying to do may not be possible, but that
doesn't mean it's not worth investigating.
Regards,
A.D.B.
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Bob Hughes wrote:
> "Christoph Hormann" <chr### [at] gmxde> wrote in message
> news:dcn984$3f2$1@chho.imagico.de...
>
>>The transmission of light is nothing that makes sense to simulate in
>>POV-Ray since it has no effect on the image POV-Ray renders (light itself
>>isn't visible). Therefore using emitting media for the glow and placing a
>>spotlight at the end is the way to go.
>
>
> I don't think I can debate you on that, especially since I'm not sure what
> you meant by "no effect on the image", but never say never. Not sure what
> all Anthony knows about fiber optics but I know only enough to describe it
> to people with no knowledge of it in the first place. ;)
>
> As I might have said elsewhere already, I was once able to get a simulated
> fiber optic cable made in POV and at least partially succeeded (maybe). It
> was done by using photons and reflection on the inside of an S-shaped
> sphere_sweep. I think it is total internal reflection effect, I believe,
> that is the operative factor IRL. Meaning, the boundary of the tube with the
> air is supposed to cause the light to stay within the tube walls because of
> a specific limiting angle whereby light only reflects instead of breaks
> through.
>
> My test scene wasn't very good for anything as I recall, and I was counting
> on faking it with reflection, not refraction. I'm not good enough with
> photons to be sure if it really works or not anyway. I guess there would be
> trouble due to how the photons are designed to map out into the scene, not
> very sure of anything about it though. Probably was never designed to bounce
> around inside of curving tubes.
>
> Sure hope you can manage to do something with your idea, Anthony. I just
> found the test scene I had done and rendered it as-is. Only got a bunch of
> red spots everywhere, mostly at the ground beyond the opposite end of the
> tube. Probably wouldn't help to see the scene yourself, it's basically just
> a narrow spotlight close to one end of that sphere_sweep (hollowed out with
> a smaller twin), which then has refraction and reflection including
> interior_texture.
>
> I just looked for info about TIR and fiber optics and there's mention of
> critical angles for the light entering the tube and the bends in the tube.
> Gets beyond me but this one web page allows for calculating the critical
> incidence angle for different ior, if you're interested.
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html
>
> Bob
>
>
Hi Bob,
I don't really know that much about them, only what a quick google
search could tell me.
That being said, I did find out that the coating layer has a lower IOR
than the fiber core. This is explained by that link you posted. When
passing through one medium strikes a medium with a lesser IOR, "the ray
is bent away from the normal." Thus, the angle of reflection will be
greater than the incident angle. (I can picture this. That doesn't mean
that I completely understand it.)
I do however see Christoph's point about max_trace_level.
Thanks for the link.
Regards,
A.D.B.
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Cool idea!
> >>The transmission of light is nothing that makes sense to simulate in
> >>POV-Ray since it has no effect on the image POV-Ray renders (light itself
> >>isn't visible). Therefore using emitting media for the glow and placing a
> >>spotlight at the end is the way to go.
A MUCH faster way to get the "points of light" at the ends of the fibers
(like in a flower sculpture) might be to attach spheres at the end the same
diameter as the cable. Give them a high ambience.
>
> That being said, I did find out that the coating layer has a lower IOR
> than the fiber core. This is explained by that link you posted. When
> passing through one medium strikes a medium with a lesser IOR, "the ray
> is bent away from the normal." Thus, the angle of reflection will be
> greater than the incident angle. (I can picture this. That doesn't mean
> that I completely understand it.)
This might actually be made to work with photons, although be prepared to
have your swap file limit increased to an astonomical size and a LONG
render time! I'd love to experiment just now but MY machine is 15 hours
into a major render with photons and my swap file just expanded to over two
gigs :o( One potential problem I forsee is the dreaded co-incident surface
bug. Photons only refract when entering (or leaving, depending on your
point of view) an object. An object can only have one ior in it's
interior. So to simulate two ior's I'd put a solid sphere sweep with high
ior inside a larger, hollowed out (NOT hollow) sphere sweep with a lower
one. Make sure the inner one is a little bigger than the hollow in the
outer one is, which prevents a co-incident surface, and then merge the two
together to remove interior surfaces. A lot of this is personal conjecture
on my part but it's where I'll start next week when I get POV back again.
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Lonnie wrote:
> Cool idea!
>
>
>>>>The transmission of light is nothing that makes sense to simulate in
>>>>POV-Ray since it has no effect on the image POV-Ray renders (light itself
>>>>isn't visible). Therefore using emitting media for the glow and placing a
>>>>spotlight at the end is the way to go.
>
>
> A MUCH faster way to get the "points of light" at the ends of the fibers
> (like in a flower sculpture) might be to attach spheres at the end the same
> diameter as the cable. Give them a high ambience.
>
>
>> That being said, I did find out that the coating layer has a lower IOR
>>than the fiber core. This is explained by that link you posted. When
>>passing through one medium strikes a medium with a lesser IOR, "the ray
>>is bent away from the normal." Thus, the angle of reflection will be
>>greater than the incident angle. (I can picture this. That doesn't mean
>>that I completely understand it.)
>
>
> This might actually be made to work with photons, although be prepared to
> have your swap file limit increased to an astonomical size and a LONG
> render time!
>
>
What's a swap file?
I'm on a Mac. maybe it's called something else.
A.D.B.
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Christoph Hormann wrote:
> Anthony D. Baye wrote:
>
>>
>> So my question is: Is there an eficient way to model Optical
>> fibers, so that they not only glow, but transmit the light along the
>> length as well.
>> Naturally, I'll continue my own experimentations. I would however
>> appreciate any thoughts people might have on the subject.
>
>
> The transmission of light is nothing that makes sense to simulate in
> POV-Ray since it has no effect on the image POV-Ray renders (light
> itself isn't visible). Therefore using emitting media for the glow and
> placing a spotlight at the end is the way to go.
>
> Christoph
>
Something else I just thought of:
Light is radiation in the visible spectrum.
In the real world, you can't have radiation in the visible spectrum
without an object present to give off said radiation.
so when you look at a light bulb, it's not really the light you're
seeing, but the glowing filament, and the light bulb of course.
But this is fairly elementary stuff.
In the case of Optical Fibers, it's not really the light that's being
seen, but the reflection off the interior surface of the fiber.
I'll admit, Lonnie has a point about 'gluing' ambient spheres to the
edges of an object. I hadn't thought of this, because I have absolutely
no idea how to use the trace macro. (I assume I'd need it.)
It's nice that this is the subject of so much discussion though.
Regards,
A.D.B.
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