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/

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> 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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