First of all, do I have the basic concept right?  The docs are incomplete.
My feeling is that using photons in the global_settings will cause all light
sources to shoot photons at objects that have reflection/refraction photons
turned on, and then =all= objects (unless marked ignore) are illuminated by
these photons.

What are "global photons", as in "Light sources can also generate global
photons. To enable this feature, put the keyword global in the light
source's photon block." ?

A glass object's shadow is totally black
(http://green.dlugosz.com/files/photon_try_1.jpg ).  Why is this, and how
can I get the shadow lighter?

--John

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In article <3aabe409$1@news.povray.org> , "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> What are "global photons", as in "Light sources can also generate global
> photons. To enable this feature, put the keyword global in the light
> source's photon block." ?

Using "global_photons" is not recommended right now (because they don't
work perfectly, they are kind of experimental).  For now you should only
use photons for individual objects as explained in the MegaPOV
documentation and sample files.  Doing so will assume compatibility of
your scene with POV-Ray 3.5.


      Thorsten


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

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

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Are you saying simply don't use the "global" keyword in either place (light
source or global_settings), and the rest of the example in the manual is OK?
That is, there is still stuff in the "global_settings" block -- that has
nothing to do with global photons?

And just what are global photons?

--John

"Thorsten Froehlich" <tho### [at] trfde> wrote in message
news:3aac260b@news.povray.org...
> In article <3aabe409$1@news.povray.org> , "John M. Dlugosz"
> <joh### [at] dlugoszcom> wrote:
>
> > What are "global photons", as in "Light sources can also generate global
> > photons. To enable this feature, put the keyword global in the light
> > source's photon block." ?
>
> Using "global_photons" is not recommended right now (because they don't
> work perfectly, they are kind of experimental).  For now you should only
> use photons for individual objects as explained in the MegaPOV
> documentation and sample files.  Doing so will assume compatibility of
> your scene with POV-Ray 3.5.
>
>
>       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

In article <3aad6f56$1@news.povray.org> , "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> Are you saying simply don't use the "global" keyword in either place (light
> source or global_settings), and the rest of the example in the manual is OK?
> That is, there is still stuff in the "global_settings" block -- that has
> nothing to do with global photons?

Exactly.  Only the "global" keyword should not be used.

> And just what are global photons?

Photons that are "everywhere" compared to those that only work on
individual objects.


    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

In article <3aabe409$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> A glass object's shadow is totally black
> (http://green.dlugosz.com/files/photon_try_1.jpg ).  Why is this,

It happens because almost all light is being refracted away from those 
areas.


> and how can I get the shadow lighter?

Use radiosity to get indirect illumination from surrounding objects and 
that media glow in the middle, and/or use more light sources to 
illuminate the shadows.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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That brings up a deeper question of just how photons work.  That is, it
seems to take the place of regular shadow calculations?  Hmm, I suppose it
works by saying that any object that uses photons will turn completely
opaque to the regular lighting code, and any light that comes through will
be added by the photon illumination instead.

And you answered another question as well, and that being whether radiosity
can be used with photons or if photons takes the place of (is a superset of)
radiosity.

Any idea what causes the black streak in the middle of the wall?  I always
figured it was a shadow of the tip of the glass, but the streak is in all
directions, not just where the tip is.

Thanks for the insight, as always.

--John

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-2D35C4.22070612032001@news.povray.org...
> In article <3aabe409$1@news.povray.org>, "John M. Dlugosz"
> <joh### [at] dlugoszcom> wrote:
>
> > A glass object's shadow is totally black
> > (http://green.dlugosz.com/files/photon_try_1.jpg ).  Why is this,
>
> It happens because almost all light is being refracted away from those
> areas.
>
>
> > and how can I get the shadow lighter?
>
> Use radiosity to get indirect illumination from surrounding objects and
> that media glow in the middle, and/or use more light sources to
> illuminate the shadows.
>
> --
> Christopher James Huff
> Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
> TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
>
> <><

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"John M. Dlugosz" wrote:

> Any idea what causes the black streak in the middle of the wall?  I always
> figured it was a shadow of the tip of the glass, but the streak is in all
> directions, not just where the tip is.

It's not a shadow. What kind of object was used to create the wall ?

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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In article <3aaec0db$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> Any idea what causes the black streak in the middle of the wall?  I 
> always figured it was a shadow of the tip of the glass, but the 
> streak is in all directions, not just where the tip is.

It looks like a solver error...is the wall or glass a sor, lathe, poly, 
or anything else which can use the sturmian root solver? If so, did you 
try using "sturm" or moving the camera/light source around a bit?

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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"Ken" <tyl### [at] pacbellnet> wrote in message
news:3AAEDE69.DF5EB5B0@pacbell.net...
>
> It's not a shadow. What kind of object was used to create the wall ?

It's supposed to be a curved wall.  Full source file is at
http://green.dlugosz.com/files/lamp1.3.pov .

That object is:

difference {
   intersection {
      cylinder { <0,0,0>, <0,18,0>, 12 }
      plane { -z, 0 }
   } // end of intersection
   cylinder { <0,0,0>, <0,18,0>, 11.5 }
   pigment { color red 0.858824 green 0.439216 blue 0.576471 }
   finish {
      ambient 0.15
      diffuse 0.6
      specular 0.6
   }
   scale <1.6,1,1>
} // end difference

Thanks for the insight,
--John

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"Chris Huff" <chr### [at] maccom> wrote in message news:chrishuff-> > Any
idea what causes the black streak in the middle of the wall?  I
> > always figured it was a shadow of the tip of the glass, but the
> > streak is in all directions, not just where the tip is.
>
> It looks like a solver error...is the wall or glass a sor, lathe, poly,
> or anything else which can use the sturmian root solver? If so, did you
> try using "sturm" or moving the camera/light source around a bit?

It's a simple curve made with a cylinder.  I tried moving the light source a
tad, nothing I can use with strum.  I posted the code in a reply to Ken.

--John

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In article <3ab00fe5@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> difference {
>    intersection {
>       cylinder { <0,0,0>, <0,18,0>, 12 }
...
>    cylinder { <0,0,0>, <0,18,0>, 11.5 }

You have a coincident surfaces problem here...try using < 0, 18.001, 0> 
in the second cylinder.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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In article <3ab01033$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> It's a simple curve made with a cylinder.  I tried moving the light 
> source a tad, nothing I can use with strum.  I posted the code in a 
> reply to Ken.

You have a quartic object! This seems to be the source of the 
problem...using "sturm" in it eliminates the line in my tests.
There are several other problems as well..."refraction" and "caustics" 
are no longer used in a finish{} statement, "refraction" is now "ior", 
and both are in interior{}. You have several coincident surfaces 
problems...mainly with cylinders and differences. You are missing a 
semicolon at the end of the declaration for "ft". However, the scene 
seems to render fine...but these should be fixed.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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That's not a coincident surface -- that's the top and bottom of cyl's with
different radii.  I agree that would be a problem if the top edge were in
the frame, but we're looking at the inside curve of the smaller one.

I tried it anyway, and it makes no difference.

--John

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-C04E3E.20015214032001@news.povray.org...
> In article <3ab00fe5@news.povray.org>, "John M. Dlugosz"
> <joh### [at] dlugoszcom> wrote:
>
> > difference {
> >    intersection {
> >       cylinder { <0,0,0>, <0,18,0>, 12 }
> ...
> >    cylinder { <0,0,0>, <0,18,0>, 11.5 }
>
> You have a coincident surfaces problem here...try using < 0, 18.001, 0>
> in the second cylinder.
>
> --
> Christopher James Huff
> Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
> TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
>
> <><

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That was it!  It never occured to me that the problem would be in a
different object than the one the scratches seemed to be on.  The glass lamp
base is the one that needed "sturm", not the back wall.

Thanks for the pointers.  I've updated some of the old syntax already, but
pointed you to a copy I made earlier, without all my current mess in it from
playing around.

The warning "Refraction value unnecessary to turn on refraction" is hard to
understand.  Does that mean that if ior is present in the interior, then
refraction is indeed ON and this statement is unnecessary?

--John

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-D2DFC9.20241514032001@news.povray.org...
> In article <3ab01033$1@news.povray.org>, "John M. Dlugosz"
> <joh### [at] dlugoszcom> wrote:
>
> > It's a simple curve made with a cylinder.  I tried moving the light
> > source a tad, nothing I can use with strum.  I posted the code in a
> > reply to Ken.
>
> You have a quartic object! This seems to be the source of the
> problem...using "sturm" in it eliminates the line in my tests.
> There are several other problems as well..."refraction" and "caustics"
> are no longer used in a finish{} statement, "refraction" is now "ior",
> and both are in interior{}. You have several coincident surfaces
> problems...mainly with cylinders and differences. You are missing a
> semicolon at the end of the declaration for "ft". However, the scene
> seems to render fine...but these should be fixed.
>
> --
> Christopher James Huff
> Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
> TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
>
> <><

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In article <3ab1659e$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> The warning "Refraction value unnecessary to turn on refraction" is 
> hard to understand.  Does that mean that if ior is present in the 
> interior, then refraction is indeed ON and this statement is 
> unnecessary?

Yes. You do not need any refraction stuff in the finish, just give an 
ior value in the interior and refraction will be turned on.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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In article <3ab16386$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> That's not a coincident surface -- that's the top and bottom of cyl's with
> different radii. 

There *are* coincident surfaces...the cylinders have different radii, 
but that doesn't make any difference, the surfaces of the ends of the 
cylinders coincide. Take another look...the end caps of the 11.5 unit 
radius cylinder are completely within the end caps of the 12 unit radius 
one. The difference in radius (and the plane in the intersection object) 
just changes the amount of area that is coincident.


> I agree that would be a problem if the top edge were in
> the frame, but we're looking at the inside curve of the smaller one.

I figured out it wasn't a problem when I looked at the complete scene 
file and saw the quartic.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

Post a reply to this message

> There *are* coincident surfaces...the cylinders have different radii,
> but that doesn't make any difference, the surfaces of the ends of the
> cylinders coincide. Take another look...the end caps of the 11.5 unit
> radius cylinder are completely within the end caps of the 12 unit radius
> one. The difference in radius (and the plane in the intersection object)
> just changes the amount of area that is coincident.

Is that a problem if that isn't in the scene?

--John

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In article <3ab2fb25$1@news.povray.org>, "John M. Dlugosz" 
<joh### [at] dlugoszcom> wrote:

> Is that a problem if that isn't in the scene?

It could be if the objects are transparent or partly transparent, or if 
there are reflections in the scene. It doesn't seem to bother this one, 
but avoiding coincident surfaces is a good habit to get into.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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> It could be if the objects are transparent or partly transparent, or if
> there are reflections in the scene. It doesn't seem to bother this one,
> but avoiding coincident surfaces is a good habit to get into.

I thought about that later, too.  I'll keep that in mind, thanks.

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